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Электронный компонент: CS5165AGDW16

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Semiconductor Components Industries, LLC, 2001
May, 2001 Rev. 0
1
Publication Order Number:
CS5165A/D
CS5165A
5-Bit Synchronous CPU
Buck Controller
The CS5165A synchronous 5bit NFET buck controller is optimized
to manage the power of the next generation Pentium II processors. It's
V
2
control architecture delivers the fastest transient response (100 ns),
and best overall voltage regulation in the industry today. It's feature rich
design gives end users the maximum flexibility to implement the best
price/performance solutions for their end products.
The CS5165A has been carefully crafted to maximize performance and
protect the processor during operation. It has a 5bit DAC on board that
holds a
1.0% tolerance over temperature. Its on board programmable Soft
Start insures a control start up, and the FET nonoverlap circuitry ensures
that both FETs do not conduct simultaneously.
The on board oscillator can be programmed up to 1.0 MHz to give
the designer maximum flexibility in choosing external components
and setting systems costs.
The CS5165A protects the processor during potentially catastrophic
events like overvoltage (OVP) and short circuit. The OVP feature is
part of the V
2
architecture and does not require any additional
components. During short circuit, the controller pulses the MOSFETs
in a "hiccup" mode (3.0% duty cycle) until the fault is removed. With
this method, the MOSFETs do not overheat or self destruct.
The CS5165A is designed for use in both single processor desktop and
multiprocessor workstation and server applications. The CS5165A's
current sharing capability allows the designer to build multiple parallel
and redundant power solutions for multiprocessor systems.
The CS5165A contains other control and protection features such as
Power Good, ENABLE, and adaptive voltage positioning. It is
available in a 16 lead SOIC wide body package.
Features
V
2
Control Topology
Dual NChannel Design
100 ns Controller Transient Response
Excess of 1.0 MHz Operation
5Bit DAC with 1.0% Tolerance
Power Good Output With Internal Delay
Enable Input Provides Micropower Shutdown Mode
5.0 V & 12 V Operation
Adaptive Voltage Positioning
Remote Sense Capability
Current Sharing Capability
V
CC
Monitor
Hiccup Mode Short Circuit Protection
Overvoltage Protection (OVP)
Programmable Soft Start
150 ns PWM Blanking
65 ns FET Nonoverlap Time
40 ns Gate Rise and Fall Times (3.3 nF Load)
CS5165AGDWR16
http://onsemi.com
A
= Assembly Location
WL, L
= Wafer Lot
YY, Y
= Year
WW, W
= Work Week
Device
Package
Shipping
ORDERING INFORMATION
CS5165AGDW16
SO16L
46 Units/Rail
SO16L
1000 Tape & Reel
PIN CONNECTIONS
SO16L
DW SUFFIX
CASE 751G
MARKING
DIAGRAM
1
CS5165A
AWLYYWW
16
V
CC
ENABLE
1
16
GATE(H)
C
OFF
PGND
V
ID4
GATE(L)
SS
PWRGD
V
ID3
LGND
V
ID2
COMP
V
ID1
V
FB
V
ID0
1
16
CS5165A
http://onsemi.com
2
Figure 1. Application Diagram, 5.0 V to 2.8 V @ 14.2 A for 300 MHz Pentium II
COMP
V
SS
V
FB
GATE(H)
V
CC
V
ID0
V
ID1
V
ID2
V
ID3
PGND
SS
C
OFF
CS5165A
PCB trace
6.0 m
12 V
330 pF
0.1
F
LGND
1200
F/10 V
3
1.0
F
Pentium II
System
V
ID0
V
ID1
V
ID2
V
ID3
1200
F/10 V
5
1.2
H
5.0 V
3.3 k
1000 pF
V
ID4
V
ID4
IRL3103
GATE(L)
0.1
F
PWRGD
ENABLE
IRL3103
ENABLE
PWRGD
V
CC
ABSOLUTE MAXIMUM RATINGS*
Rating
Value
Unit
Operating Junction Temperature, T
J
0 to 150
C
Lead Temperature Soldering:
Reflow: (SMD styles only) (Note 1.)
230 peak
C
Storage Temperature Range, T
S
65 to +150
C
ESD Susceptibility (Human Body Model)
2.0
kV
1. 60 second maximum above 183
C.
*The maximum package power dissipation must be observed.
CS5165A
http://onsemi.com
3
ABSOLUTE MAXIMUM RATINGS
Pin Name
Pin Symbol
V
MAX
V
MIN
I
SOURCE
I
SINK
IC Power Input
V
CC
16 V
0.3 V
N/A
1.5 A peak, 200 mA DC
Soft Start Capacitor
SS
6.0 V
0.3 V
200
A
10
A
Compensation Capacitor
COMP
6.0 V
0.3 V
10 mA
1.0 mA
Voltage Feedback Input
V
FB
6.0 V
0.3 V
10
A
10
A
OffTime Capacitor
C
OFF
6.0 V
0.3 V
1.0 mA
50 mA
Voltage ID DAC Inputs
V
ID0
V
ID4
6.0 V
0.3 V
1.0 mA
10
A
HighSide FET Driver
GATE(H)
16 V
0.3 V
1.5 A peak, 200 mA DC
1.5 A peak, 200 mA DC
LowSide FET Driver
GATE(L)
16 V
0.3 V
1.5 A peak, 200 mA DC
1.5 A peak, 200 mA DC
Enable Input
ENABLE
6.0 V
0.3 V
100
A
1.0 mA
Power Good Output
PWRGD
6.0 V
0.3 V
10
A
30 mA
Power Ground
PGND
0 V
0 V
1.5 A peak, 200 mA DC
N/A
Logic Ground
LGND
0 V
0 V
100 mA
N/A
ELECTRICAL CHARACTERISTICS
(0
C < T
A
< +70
C; 0
C < T
J
< +125
C; 8.0
V < V
CC
< 14
V; 2.8 DAC Code:
(V
ID4
=
V
ID2
=
V
ID1
=
V
ID0
= 1; V
ID3
= 0)
;
C
GATE(H)
and C
GATE(L)
= 3.3
nF; C
OFF
= 330 pF; C
SS
= 0.1
F, unless otherwise specified.)
Characteristic
Test Conditions
Min
Typ
Max
Unit
V
CC
Supply Current
Operating
1.0 V < V
FB
< V
DAC
(max ontime)
No Loads on GATE(H) and GATE(L)
12
20
mA
Sleep Mode
ENABLE = 0 V
300
600
A
V
CC
Monitor
Start Threshold
GATE(H) switching
3.75
3.95
4.15
V
Stop Threshold
GATE(H) not switching
3.65
3.87
4.05
V
Hysteresis
StartStop
80
mV
Error Amplifier
V
FB
Bias Current
V
FB
= 0 V
0.1
1.0
A
COMP Source Current
COMP = 1.2 V to 3.6 V; V
FB
= 2.7 V
15
30
60
A
COMP CLAMP Voltage
V
FB
= 2.7 V, Adjust COMP voltage for Comp
current = 50
A
0.85
1.0
1.15
V
COMP Clamp Current
COMP = 0 V
0.4
1.0
1.6
mA
COMP Sink Current
V
COMP
= 1.2 V; V
FB
= 3.0 V; V
SS
> 2.5 V
180
400
800
A
Open Loop Gain
Note 2.
50
60
dB
Unity Gain Bandwidth
Note 2.
0.5
2.0
MHz
PSRR @ 1.0 kHz
Note 2.
60
85
dB
GATE(H) and GATE(L)
High Voltage at 100 mA
Measure V
CC
GATE
1.2
2.0
V
Low Voltage at 100 mA
Measure GATE
1.0
1.5
V
Rise Time
1.6 V < GATE < (V
CC
2.5 V)
40
80
ns
Fall Time
(V
CC
2.5 V) > GATE > 1.6 V
40
80
ns
GATE(H) to GATE(L)
Delay
GATE(H) < 2.0 V; GATE(L) > 2.0 V
30
65
100
ns
GATE(L) to GATE(H)
Delay
GATE(L) < 2.0 V; GATE(H) > 2.0 V
30
65
100
ns
GATE pulldown
Resistor to PGND, Note 2.
20
50
115
k
2. Guaranteed by design, not 100% tested in production.
CS5165A
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4
ELECTRICAL CHARACTERISTICS (continued)
(0
C < T
A
< +70
C; 0
C < T
J
< +125
C; 8.0
V < V
CC
< 14
V; 2.8 DAC Code:
(V
ID4
=
V
ID2
=
V
ID1
=
V
ID0
= 1; V
ID3
= 0)
;
C
GATE(H)
and C
GATE(L)
= 3.3
nF; C
OFF
= 330 pF; C
SS
= 0.1
F, unless otherwise specified.)
Characteristic
Unit
Max
Typ
Min
Test Conditions
Fault Protection
SS Charge Time
V
FB
= 0 V
1.6
3.3
5.0
ms
SS Pulse Period
V
FB
= 0 V
25
100
200
ms
SS Duty Cycle
(Charge Time/Period)
100
1.0
3.3
6.0
%
SS COMP Clamp Voltage
V
FB
= 2.7 V; V
SS
= 0 V
0.50
0.95
1.10
V
V
FB
Low Comparator
Increase V
FB
till no SS pulsing and normal Offtime
0.9
1.0
1.1
V
PWM Comparator
Transient Response
V
FB
= 1.2 to 5.0 V. 500 ns after GATE(H)
(after Blanking time) to GATE(H) = (V
CC
1.0 V)
to 1.0 V
130
180
ns
Minimum Pulse Width
(Blanking Time)
Drive V
FB.
1.2 to 5.0 V upon GATE(H) rising edge
(> V
CC
1.0 V), measure GATE(H) pulse width
50
150
250
ns
C
OFF
Normal OffTime
V
FB
= 2.7 V
1.0
1.6
2.3
s
Extended OffTime
V
SS
= V
FB
= 0 V
5.0
8.0
12.0
s
TimeOut Timer
TimeOut Time
V
FB
= 2.7 V, Measure GATE(H) Pulse Width
10
30
50
s
Fault Duty Cycle
V
FB
= 0V
30
50
70
%
Enable Input
ENABLE Threshold
GATE(H) Switching
0.8
1.15
1.30
V
Shutdown delay (Note 3.)
ENABLEtoGATE(H) < 2.0 V
3.0
s
Pullup Current
ENABLE = 0 V
3.0
7.0
15
A
Pullup Voltage
No load on ENABLE pin
1.30
1.8
3.0
V
Input Resistance
ENABLE = 5.0 V, R = (5.0 V V
PULLUP
)/I
ENABLE
10
20
50
k
Power Good Output
Low to High Delay
V
FB
= (0.8
V
DAC
) to V
DAC
30
65
110
s
High to Low Delay
V
FB
= V
DAC to
(0.8
V
DAC
)
30
75
120
s
Output Low Voltage
V
FB
= 2.4 V, I
PWRGD
= 500
A
0.2
0.3
V
Sink Current Limit
V
FB
= 2.4 V, PWRGD = 1.0 V
0.5
4.0
15.0
mA
3. Guaranteed by design, not 100% tested in production.
CS5165A
http://onsemi.com
5
ELECTRICAL CHARACTERISTICS (continued)
(0
C < T
A
< +70
C; 0
C < T
J
< +125
C; 8.0
V < V
CC
< 14
V; 2.8 DAC Code:
(V
ID4
=
V
ID2
=
V
ID1
=
V
ID0
= 1; V
ID3
= 0)
;
C
GATE(H)
and C
GATE(L)
= 3.3
nF; C
OFF
= 330 pF; C
SS
= 0.1
F, unless otherwise specified.)
Characteristic
Unit
Max
Typ
Min
Test Conditions
Voltage Identification DAC
Accuracy (all codes except 11111)
Measure V
FB
= COMP (C
OFF
= 0 V)
25
C
T
J
125
C; V
CC
= 12 V
1.0
+1.0
%
V
ID4
V
ID3
V
ID2
V
ID1
V
ID0
1
0
0
0
0
3.505
3.540
3.575
V
1
0
0
0
1
3.406
3.440
3.474
V
1
0
0
1
0
3.307
3.340
3.373
V
1
0
0
1
1
3.208
3.240
3.272
V
1
0
1
0
0
3.109
3.140
3.171
V
1
0
1
0
1
3.010
3.040
3.070
V
1
0
1
1
0
2.911
2.940
2.969
V
1
0
1
1
1
2.812
2.840
2.868
V
1
1
0
0
0
2.713
2.740
2.767
V
1
1
0
0
1
2.614
2.640
2.666
V
1
1
0
1
0
2.515
2.540
2.565
V
1
1
0
1
1
2.416
2.440
2.464
V
1
1
1
0
0
2.317
2.340
2.363
V
1
1
1
0
1
2.218
2.240
2.262
V
1
1
1
1
0
2.119
2.140
2.161
V
0
0
0
0
0
2.069
2.090
2.111
V
0
0
0
0
1
2.020
2.040
2.060
V
0
0
0
1
0
1.970
1.990
2.010
V
0
0
0
1
1
1.921
1.940
1.959
V
0
0
1
0
0
1.871
1.890
1.909
V
0
0
1
0
1
1.822
1.840
1.858
V
0
0
1
1
0
1.772
1.790
1.808
V
0
0
1
1
1
1.723
1.740
1.757
V
0
1
0
0
0
1.673
1.690
1.707
V
0
1
0
0
1
1.624
1.640
1.656
V
0
1
0
1
0
1.574
1.590
1.606
V
0
1
0
1
1
1.525
1.540
1.555
V
0
1
1
0
0
1.475
1.490
1.505
V
0
1
1
0
1
1.426
1.440
1.455
V
0
1
1
1
0
1.376
1.390
1.405
V
0
1
1
1
1
1.327
1.340
1.353
V
1
1
1
1
1
1.223
1.247
1.273
V
Input Threshold
V
ID4
, V
ID3
, V
ID2
, V
ID1
, V
ID0
1.000
1.250
2.400
V
Input Pullup Resistance
V
ID4
, V
ID3
, V
ID2
, V
ID1
, V
ID0
25
50
100
k
Input Pullup Voltage
4.85
5.00
5.15
V
CS5165A
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6
ELECTRICAL CHARACTERISTICS (continued)
(0
C < T
A
< +70
C; 0
C < T
J
< +125
C; 8.0
V < V
CC
< 14
V; 2.8 DAC Code:
(V
ID4
=
V
ID2
=
V
ID1
=
V
ID0
= 1; V
ID3
= 0)
;
C
GATE(H)
and C
GATE(L)
= 3.3
nF; C
OFF
= 330 pF; C
SS
= 0.1
F, unless otherwise specified.)
Thre hold Acc r cy
Lower Threshold
Upper Threshold
Threshold Accuracy
Min
Typ
Max
Min
Typ
Max
Unit
DAC CODE
% of Nominal DAC Output
12
8.5
5.0
5.0
8.5
12
%
V
ID4
V
ID3
V
ID2
V
ID1
V
ID0
1
0
0
0
0
3.115
3.239
3.363
3.717
3.841
3.965
V
1
0
0
0
1
3.027
3.148
3.268
3.612
3.732
3.853
V
1
0
0
1
0
2.939
3.056
3.173
3.507
3.624
3.741
V
1
0
0
1
1
2.851
2.965
3.078
3.402
3.515
3.629
V
1
0
1
0
0
2.763
2.873
2.983
3.297
3.407
3.517
V
1
0
1
0
1
2.675
2.782
2.888
3.192
3.298
3.405
V
1
0
1
1
0
2.587
2.690
2.793
3.087
3.190
3.293
V
1
0
1
1
1
2.499
2.599
2.698
2.982
3.081
3.181
V
1
1
0
0
0
2.411
2.507
2.603
2.877
2.973
3.069
V
1
1
0
0
1
2.323
2.416
2.508
2.772
2.864
2.957
V
1
1
0
1
0
2.235
2.324
2.413
2.667
2.756
2.845
V
1
1
0
1
1
2.147
2.233
2.318
2.562
2.647
2.733
V
1
1
1
0
0
2.059
2.141
2.223
2.457
2.539
2.621
V
1
1
1
0
1
1.971
2.050
2.128
2.352
2.430
2.509
V
1
1
1
1
0
1.883
1.958
2.033
2.250
2.322
2.397
V
0
0
0
0
0
1.839
1.912
1.986
2.195
2.268
2.341
V
0
0
0
0
1
1.795
1.867
1.938
2.142
2.213
2.285
V
0
0
0
1
0
1.751
1.821
1.810
2.090
2.159
2.229
V
0
0
0
1
1
1.707
1.775
1.843
2.037
2.105
2.173
V
0
0
1
0
0
1.663
1.729
1.796
1.985
2.051
2.117
V
0
0
1
0
1
1.619
1.684
1.748
1.932
1.996
2.061
V
0
0
1
1
0
1.575
1.638
1.701
1.880
1.942
2.005
V
0
0
1
1
1
1.531
1.592
1.653
1.827
1.888
1.949
V
0
1
0
0
0
1.487
1.546
1.606
1.775
1.834
1.893
V
0
1
0
0
1
1.443
1.501
1.558
1.722
1.779
1.837
V
0
1
0
1
0
1.399
1.455
1.511
1.670
1.725
1.781
V
0
1
0
1
1
1.355
1.409
1.463
1.617
1.671
1.724
V
0
1
1
0
0
1.311
1.363
1.416
1.565
1.617
1.669
V
0
1
1
0
1
1.267
1.318
1.368
1.512
1.562
1.613
V
0
1
1
1
0
1.223
1.272
1.321
1.460
1.508
1.557
V
0
1
1
1
1
1.179
1.226
1.273
1.407
1.454
1.501
V
1
1
1
1
1
1.097
1.141
1.185
1.309
1.353
1.397
V
CS5165A
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7
PACKAGE PIN DESCRIPTION
PACKAGE PIN #
SO16L
PIN SYMBOL
FUNCTION
1, 2, 3, 4, 6
V
ID0
V
ID4
Voltage ID DAC input pins. These pins are internally pulled up to 5.0 V if left open. V
ID4
selects the DAC range. When V
ID4
is high (logic one), the Error Amp reference range is
2.14 V to 3.45 V with 100 mV increments. When V
ID4
is low (logic zero), the Error Amp
reference voltage 1.34 V to 2.09 V with 50 mV increments.
5
SS
Soft Start Pin. A capacitor from this pin to LGND sets the Soft Start and fault timing.
7
C
OFF
OffTime Capacitor Pin. A capacitor from this pin to LGND sets both the normal and
extended off time.
8
ENABLE
Output Enable Input. This pin is internally pulled up to 1.8 V. A logic Low (< 0.8) on this
pin disables operation and places the CS5165A into a low current sleep mode.
9
V
CC
Input Power Supply Pin.
10
GATE(H)
High Side Switch FET driver pin.
11
PGND
High current ground for the GATE(H) and GATE(L) pins.
12
GATE(L)
Low Side Synchronous FET driver pin.
13
PWRGD
Power Good Output. Open collector output drives low when V
FB
is out of regulation. Ac-
tive when ENABLE input is low.
14
LGND
Reference ground. All control circuits are referenced to this pin.
15
COMP
Error Amp output. PWM Comparator reference input. A capacitor to LGND provides Error
Amp compensation.
16
V
FB
Error Amp, PWM Comparator, and Low V
FB
Comparator feedback input.
CS5165A
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8
Figure 2. Block Diagram
ENABLE
SS
V
ID0
V
ID1
V
ID2
V
ID3
V
ID4
V
FB
Low
Comparator
PWRGD
LGND
PWM
Comparator
SS Low
Comparator
SS High
Comparator
V
CC
Monitor
Error Amplifier
V
CC1
V
CC
C
OFF
V
GATE(H)
V
GATE(L)
PGND
FAULT
FAULT
FAULT
Latch
PGND
R
S
Q
Q
R
S
Q
Q
R
S
Q
Latch
PWM
C
OFF
One Shot
OffTime
Timeout
Edge Triggered
Extended
OffTime
Timeout
Normal
OffTime
Timeout
Maximum
OnTime
Timeout
GATE(H) = ON
GATE(H) = OFF
2.0
A
60
A
5.0 V
0.7 V
2.5 V
1.0 V
3.95 V
3.87V
V
FB
COMP
PWM COMP
+
V
CC
V
CC
TimeOut
Timer
(30
s)
Enable
Comparator
Circuit Bias
8.5%
+8.5%
+
+
+
+
+
+
+
+
1.25 V
20 k
7.0
A
5 BIT
DAC
65
s
Delay
Blanking
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TYPICAL PERFORMANCE CHARACTERISTICS
0
2000 4000
6000 8000 10000 12000 14000 16000
0
20
40
60
80
100
120
140
160
180
200
Load Capacitance (pF)
Risetime (ns)
0
2000 4000
6000 8000 10000 12000 14000 16000
0
20
40
60
80
100
120
140
160
180
200
Load Capacitance (pF)
Falltime (ns)
0
2000
4000
6000 8000 10000 12000 14000 16000
0
20
40
60
80
100
120
140
160
180
200
Load Capacitance (pF)
Risetime (ns)
0
20
40
60
100
120
0.1
80
0.08
0.06
0.04
0.02
0
0.02
0.04
Junction Temperature (
C)
DAC Output V
oltage Deviation (%)
Figure 3. GATE(L) Risetime vs. Load Capacitance
Figure 4. GATE(H) Risetime vs. Load Capacitance
Figure 5. GATE(H) & GATE(L) Falltime vs. Load
Capacitance
Figure 6. DAC Output Voltage vs. Temperature,
DAC Code = 10111, V
CC
= 12 V
V
CC
= 12 V
T
A
= 25
C
V
CC
= 12 V
T
A
= 25
C
2.14
2.24
2.34
2.44
2.54
2.64
2.74
2.84
2.94
3.04
3.14
3.24
3.34
3.54
3.44
0.25
0.20
0.15
0.10
0.05
0
0.05
1.34
1.39
1.44
1.49
1.54
1.59
1.64
1.69
1.74
1.79
1.84
1.89
1.94
2.04
1.99
0.10
0.08
0.06
0.04
0.02
0
0.04
0.02
2.09
Figure 7. Percent Output Error vs. DAC Voltage
Setting, V
CC
= 12 V, T
A
= 25
5
C, V
ID4
= 0
DAC Output Voltage Setting (V)
Figure 8. Percent Output Error vs. DAC Output
Voltage Setting V
CC
= 12 V, T
A
= 25
5
C, V
ID4
= 1
DAC Output Voltage Setting (V)
Output Error (%)
Output Error (%)
V
CC
= 12 V
T
A
= 25
C
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APPLICATIONS INFORMATION
THEORY OF OPERATION
V
2
Control Method
The V
2
method of control uses a ramp signal that is
generated by the ESR of the output capacitors. This ramp is
proportional to the AC current through the main inductor
and is offset by the value of the DC output voltage. This
control scheme inherently compensates for variation in
either line or load conditions, since the ramp signal is
generated from the output voltage itself. This control
scheme differs from traditional techniques such as voltage
mode, which generates an artificial ramp, and current mode,
which generates a ramp from inductor current.
Figure 9. V
2
Control Diagram
COMP
Reference
Voltage
+
+
PWM
Comparator
Ramp
Signal
Error
Amplifier
Error
Signal
Output
Voltage
Feedback
GATE(L)
E
C
GATE(H)
The V
2
control method is illustrated in Figure 9. The
output voltage is used to generate both the error signal and
the ramp signal. Since the ramp signal is simply the output
voltage, it is affected by any change in the output regardless
of the origin of that change. The ramp signal also contains
the DC portion of the output voltage, which allows the
control circuit to drive the main switch to 0% or 100% duty
cycle as required.
A change in line voltage changes the current ramp in the
inductor, affecting the ramp signal, which causes the V
2
control scheme to compensate the duty cycle. Since the
change in inductor current modifies the ramp signal, as in
current mode control, the V
2
control scheme has the same
advantages in line transient response.
A change in load current will have an affect on the output
voltage, altering the ramp signal. A load step immediately
changes the state of the comparator output, which controls
the main switch. Load transient response is determined only
by the comparator response time and the transition speed of
the main switch. The reaction time to an output load step has
no relation to the crossover frequency of the error signal
loop, as in traditional control methods.
The error signal loop can have a low crossover frequency,
since transient response is handled by the ramp signal loop.
The main purpose of this `slow' feedback loop is to provide
DC accuracy. Noise immunity is significantly improved,
since the error amplifier bandwidth can be rolled off at a low
frequency. Enhanced noise immunity improves remote
sensing of the output voltage, since the noise associated with
long feedback traces can be effectively filtered.
Line and load regulation are drastically improved because
there are two independent voltage loops. A voltage mode
controller relies on a change in the error signal to
compensate for a deviation in either line or load voltage.
This change in the error signal causes the output voltage to
change corresponding to the gain of the error amplifier,
which is normally specified as line and load regulation. A
current mode controller maintains fixed error signal under
deviation in the line voltage, since the slope of the ramp
signal changes, but still relies on a change in the error signal
for a deviation in load. The V
2
method of control maintains
a fixed error signal for both line and load variation, since the
ramp signal is affected by both line and load.
Constant Off Time
To maximize transient response, the CS5165A uses a
constant off time method to control the rate of output pulses.
During normal operation, the off time of the high side switch
is terminated after a fixed period, set by the C
OFF
capacitor.
To maintain regulation, the V
2
control loop varies switch on
time. The PWM comparator monitors the output voltage
ramp, and terminates the switch on time.
Constant off time provides a number of advantages.
Switch duty cycle can be adjusted from 0 to 100% on a pulse
by pulse basis when responding to transient conditions. Both
0% and 100% duty cycle operation can be maintained for
extended periods of time in response to load or line
transients. PWM slope compensation to avoid
subharmonic oscillations at high duty cycles is avoided.
Switch on time is limited by an internal 30
s (typical)
timer, minimizing stress to the power components.
Programmable Output
The CS5165A is designed to provide two methods for
programming the output voltage of the power supply. A five
bit on board digital to analog converter (DAC) is used to
program the output voltage within two different ranges. The
first range is 2.14 V to 3.54 V in 100 mV steps, the second
is 1.34 V to 2.09 V in 50 mV steps, depending on the digital
input code. If all five bits are left open, the CS5165A enters
adjust mode. In adjust mode, the designer can choose any
output voltage by using resistor divider feedback to the V
FB
pin, as in traditional controllers. The CS5165A is
specifically designed to meet or exceed Intel's Pentium II
specifications.
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11
Start Up
Until the voltage on the V
CC
supply pin exceeds the 3.95 V
monitor threshold, the Soft Start and GATE pins are held
low. The FAULT latch is reset (no Fault condition). The
output of the error amplifier (COMP) is pulled up to 1.0 V by
the comparator clamp. When the V
CC
pin exceeds the
monitor threshold, the GATE(H) output is activated, and the
Soft Start capacitor begins charging. The GATE(H) output
will remain on, enabling the NFET switch, until terminated
by either the PWM comparator, or the maximum on time
timer.
If the maximum on time is exceeded before the regulator
output voltage achieves the 1.0 V level, the pulse is
terminated. The GATE(H) pin drives low, and the GATE(L)
pin drives high for the duration of the extended off time. This
time is set by the time out timer and is approximately equal
to the maximum on time, resulting in a 50% duty cycle. The
GATE(L) pin will then drive low, the GATE(H) pin will
drive high, and the cycle repeats.
When regulator output voltage achieves the 1.0 V level
present at the COMP pin, regulation has been achieved and
normal off time will ensue. The PWM comparator
terminates the switch on time, with off time set by the C
OFF
capacitor. The V
2
control loop will adjust switch duty cycle
as required to ensure the regulator output voltage tracks the
output of the error amplifier.
The Soft Start and COMP capacitors will charge to their
final levels, providing a controlled turn on of the regulator
output. Regulator turn on time is determined by the COMP
capacitor charging to its final value. Its voltage is limited by
the Soft Start COMP clamp and the voltage on the Soft Start
pin.
Power Supply Sequencing
The CS5165A offers inherent protection from undefined
start up conditions, regardless of the 12 V and 5.0 V supply
power up sequencing. The turn on slew rates of the 12 V and
5.0 V power supplies can be varied over wide ranges without
affecting the output voltage or causing detrimental effects to
the buck regulator.
Figure 10. Demonstration Board Startup in Response
to Increasing 12 V and 5.0 V Input Voltages. Extended
Off Time is Followed by Normal Off Time Operation
when Output Voltage Achieves Regulation to the Error
Amplifier Output.
M 250
s
Trace 3 12 V Input (V
CC
) (5.0 V/div.)
Trace 1 Regulator Output Voltage (1.0 V/div.)
Trace 4 5.0 V Input (1.0 V/div.)
Trace 2 Inductor Switching Node (2.0 V/div.)
Figure 11. Demonstration Board Startup Waveforms
Trace 2 COMP PIn (error amplifier output) (1.0 V/div.)
Trace 1 Soft Start Pin (2.0 V/div.)
Trace 4 Regulator Output Voltage (1.0 V/div.)
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Figure 12. Demonstration Board Enable Startup
Waveforms
M 10.0
s
Trace 1 Regulator Output Voltage (1.0 V/div.)
Trace 2 Inductor Switching Node (5.0 V/div.)
Normal Operation
During normal operation, switch off time is constant and
set by the C
OFF
capacitor. Switch on time is adjusted by the
V
2
control loop to maintain regulation. This results in
changes in regulator switching frequency, duty cycle, and
output ripple in response to changes in load and line. Output
voltage ripple will be determined by inductor ripple current
working and the ESR of the output capacitors (see Figures
13 and 14).
Figure 13. Normal Operation Showing Output
Inductor Ripple Current and Output Voltage
Ripple, 0.5 A Load, V
OUT
= +2.84 V (DAC = 10111)
Trace 1 GATE(H) (10 V/div.)
Trace 2 Inductor Switching Node (5.0 V/div.)
Trace 3 Output Inductor Ripple Current (2.0 A/div.)
Trace 4 V
OUT
ripple (20 mV/div.)
Trace 1 GATE(H) (10 V/div.)
Trace 2 Inductor Switching Node (5.0 V/div.)
Trace 3 Output Inductor Ripple Current (2.0 A/div.)
Trace 4 V
OUT
ripple (20 mV/div.)
Figure 14. Normal Operation Showing Output
Inductor Ripple Current and Output Voltage
Ripple, I
LOAD
= 14 A, V
OUT
= +2.84 V (DAC = 10111)
Transient Response
The CS5165A V
2
control loop's 100 ns reaction time
provides unprecedented transient response to changes in
input voltage or output current. Pulse by pulse adjustment of
duty cycle is provided to quickly ramp the inductor current
to the required level. Since the inductor current cannot be
changed instantaneously, regulation is maintained by the
output capacitor(s) during the time required to slew the
inductor current.
Overall load transient response is further improved
through a feature called "Adaptive Voltage Positioning".
This technique prepositions the output capacitors voltage
to reduce total output voltage excursions during changes in
load.
Holding tolerance to 1.0% allows the error amplifiers
reference voltage to be targeted +40 mV high without
compromising DC accuracy. A "Droop Resistor",
implemented through a PC board trace, connects the Error
Amps feedback pin (V
FB
) to the output capacitors and load
and carries the output current. With no load, there is no DC
drop across this resistor, producing an output voltage
tracking the Error amps, including the +40 mV offset. When
the full load current is delivered, an 80 mV drop is developed
across this resistor. This results in output voltage being
offset 40 mV low.
The result of Adaptive Voltage Positioning is that
additional margin is provided for a load transient before
reaching the output voltage specification limits. When load
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13
current suddenly increases from its minimum level, the
output capacitor is prepositioned +40 mV. Conversely,
when load current suddenly decreases from its maximum
level, the output capacitor is prepositioned 40 mV (see
Figures 15, 16, and 17). For best Transient Response, a
combination of a number of high frequency and bulk output
capacitors are usually used.
If the Maximum OnTime is exceeded while responding
to a sudden increase in Load current, a normal offtime
occurs to prevent saturation of the output inductor.
Figure 15. Output Voltage Transient Response to
a 14 A Load Pulse, V
OUT
= +2.84 V (DAC = 10111)
Trace 4 V
OUT
(100 mV/div.)
Trace 3 Load Current (5.0 A/10 mV/div.)
Figure 16. Output Voltage Transient Response to a
14 A Load Step, V
OUT
= +2.84 V (DAC = 10111)
Trace 1 GATE(H) (10 V/div.)
Trace 2 Inductor Switching Node (5.0 V/div.)
Trace 3 Load Current (5.0 A/div)
Trace 4 V
OUT
(100 mV/div.)
Figure 17. Output Voltage Transient Response to a 14
A Load TurnOff, V
OUT
= +2.84 V (DAC = 10111)
Trace 1 GATE(H) (10 V/div.)
Trace 2 Inductor Switching Node (5.0 V/div.)
Trace 3 Load Current (5.0 A/div)
Trace 4 V
OUT
(100 mV/div.)
PROTECTION AND MONITORING FEATURES
Short Circuit Protection
A lossless hiccup mode short circuit protection feature is
provided, requiring only the Soft Start capacitor to
implement. If a short circuit condition occurs the V
FB
low
comparator sets the FAULT latch. This causes the top FET
to shut off, disconnecting the regulator from it's input
voltage. The Soft Start capacitor is then slowly discharged
by a 2.0
A current source until it reaches it's lower 0.7 V
threshold. The regulator will then attempt to restart
normally, operating in it's extended off time mode with a
50% duty cycle, while the Soft Start capacitor is charged
with a 60
A charge current.
If the short circuit condition persists, the regulator output
will not achieve the 1.0 V low V
FB
comparator threshold
before the Soft Start capacitor is charged to it's upper 2.5 V
threshold. If this happens the cycle will repeat itself until the
short is removed. The Soft Start charge/discharge current
ratio sets the duty cycle for the pulses (2.0
A/60
A =
3.3%), while actual duty cycle is half that due to the
extended off time mode (1.65%).
This protection feature results in less stress to the
regulator components, input power supply, and PC board
traces than occurs with constant current limit protection (see
Figures 18 and 19).
If the short circuit condition is removed, output voltage
will rise above the 1.0 V level, preventing the FAULT latch
from being set, allowing normal operation to resume.
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14
Figure 18. Demonstration Board Hiccup Mode Short
Circuit Protection. Gate Pulses are Delivered While
the Soft Start Capacitor Charges, and Cease During
Discharge
M 25.0 ms
Trace 3 Soft Start Timing Capacitor (1.0 V/div.)
Trace 4 5.0 V Supply Voltage (2.0 V/div.)
Trace 2 Inductor Switching Node (2.0 V/div.)
Figure 19. Demonstration Board Startup with
Regulator Output Shorted To Ground
M 50.0
s
Trace 4 5.0 V from PC Power Supply (2.0 V/div.)
Trace 2 Inductor Switching Node (2.0 V/div.)
Overvoltage Protection
Overvoltage protection (OVP) is provided as result of the
normal operation of the V
2
control topology and requires no
additional external components. The control loop responds
to an overvoltage condition within 100 ns, causing the top
MOSFET to shut off, disconnecting the regulator from it's
input voltage. The bottom MOSFET is then activated,
resulting in a "crowbar" action to clamp the output voltage
and prevent damage to the load (see Figures 20 and 21 ). The
regulator will remain in this state until the overvoltage
condition ceases or the input voltage is pulled low. The
bottom FET and board trace must be properly designed to
implement the OVP function. If a dedicated OVP output is
required, it can be implemented using the circuit in Figure
22. In this figure the OVP signal will go high (overvoltage
condition), if the output voltage (V
CORE
) exceeds 20% of
the voltage set by the particular DAC code and provided that
PWRGD is low. It is also required that the overvoltage
condition be present for at least the PWRGD delay time for
the OVP signal to be activated. The resistor values shown in
Figure 22 are for V
DAC
= +2.8 V (DAC = 10111). The V
OVP
(overvoltage trippoint) can be set using the following
equation:
VOVP
+
VBEQ3 1
)
R2
R1
Figure 20. OVP Response to an InputtoOutput
Short Circuit by Immediately Providing 0% Duty
Cycle, CrowBarring the Input Voltage to Ground
M 10.0
s
Trace 1 Regulator Output Voltage (1.0 V/div.)
Trace 2 Inductor Switching Node 5.0 V/div.)
Trace 4 5.0 V from PC Power Supply (5.0 V/div.)
Figure 21. OVP Response to an InputtoOutput Short
Circuit by Pulling the Input Voltage to Ground
M 5.00 ms
Trace 1 Regulator Output Voltage (1.0 V/div.)
Trace 4 5.0 V from PC Power Supply (2.0 V/div.)
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Figure 22. Circuit To Implement A Dedicated OVP
Output Using The CS5165A
CS5165A
PWRGD
+5.0 V
10 k
Q1
2N3906
2N3904
Q2
20 k
5.0 k
+5.0 V
10 k
10 K
OVP
Q3
2N3906
56 k
15 k
V
CORE
R1
R2
Output Enable Circuit
The Enable pin (pin 8) is used to enable or disable the
regulator output voltage, and is consistent with TTL DC
specifications. It is internally pulledup. If pulled low
(below 0.8 V), the output voltage is disabled. At the same
time the Power Good and Soft Start pins are pulled low, so
that when normal operation resumes powerup of the
CS5165A goes through the Soft Start sequence. Upon
pulling the Enable pin low, the internal IC bias is completely
shut off, resulting in total shutdown of the Controller IC.
Power Good Circuit
The Power Good pin (pin 13) is an opencollector signal
consistent with TTL DC specifications. It is externally
pulledup, and is pulled low (below 0.3 V) when the
regulator output voltage typically exceeds
8.5% of the
nominal output voltage. Maximum output voltage deviation
before Power Good is pulled low is
12%.
Figure 23. PWRGD Signal Becomes Logic High as
V
OUT
Enters 8.5% of Lower PWRGD Threshold,
V
OUT
= +2.84 V (DAC = 10111)
Trace 4 V
OUT
(1.0 V/div.)
Trace 2 PWRGD (2.0 V/div.)
Figure 24. Power Good Response to an Out of
Regulation Condition
Trace 4 V
FB
(1.0 V/div.)
Trace 2 PWRGD (2.0 V/div.)
Figure 24 shows the relationship between the regulated
output voltage V
FB
and the Power Good signal. To prevent
Power Good from interrupting the CPU unnecessarily, the
CS5165A has a builtin delay to prevent noise at the V
FB
pin
from toggling Power Good. The internal time delay is
designed to take about 75
s for Power Good to go low and
65
s for it to recover. This allows the Power Good signal to
be completely insensitive to out of regulation conditions that
are present for a duration less than the built in delay (see
Figure 25).
It is therefore required that the output voltage attains an
out of regulation or in regulation level for at least the builtin
delay time duration before the Power Good signal can
change state.
Figure 25. Power Good is Insensitive to Out of
Regulation Conditions that are Present for a
Duration Less Than the Built In Delay
Trace 4 V
FB
(1.0 V/div.)
Trace 2 PWRGD (2.0 V/div.)
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Selecting External Components
The CS5165A buck regulator can be used with a wide
range of external power components to optimize the cost and
performance of a particular design. The following
information can be used as general guidelines to assist in
their selection.
NFET Power Transistors
Both logic level and standard FETs can be used. The
reference designs derive gate drive from the 12 V supply
which is generally available in most computer systems and
utilize logic level FETs. A charge pump may be easily
implemented to support 5.0 V only systems. Multiple FET's
may be paralleled to reduce losses and improve efficiency
and thermal management.
Voltage applied to the FET gates depends on the
application circuit used. Both upper and lower gate driver
outputs are specified to drive to within 1.5 V of ground when
in the low state and to within 2.0 V of their respective bias
supplies when in the high state. In practice, the FET gates
will be driven rail to rail due to overshoot caused by the
capacitive load they present to the controller IC. For the
typical application where V
CC
= 12 V and 5.0 V is used as
the source for the regulator output current, the following
gate drive is provided:
VGS(BOTTOM)
+
12 V
VGS(TOP)
+
12 V
*
5.0 V
+
7.0 V
(see Figure 26)
Figure 26. Gate Drive Waveforms Depicting
Rail to Rail Swing
Trace 3 GATE(H) (10 V/div.)
Trace 1 GATE(H) 5.0 V
IN
Trace 4 GATE(L) (10 V/div.)
Trace 2 Inductor Switching Node (5.0 V/div.)
Figure 27. Normal Operation Showing the Guaranteed
NonOverlap Time Between the High and LowSide
MOSFET Gate Drives, I
LOAD
= 14 A
Trace 1 =
GATE(H)
(5.0 V/div.)
Trace 2 = GATE(L) (5.0 V/div.)
@ 2.2 V
The CS5165A provides adaptive control of the external
NFET conduction times by guaranteeing a typical 65 ns
nonoverlap between the upper and lower MOSFET gate
drive pulses. This feature eliminates the potentially
catastrophic effect of "shootthrough current", a condition
during which both FETs conduct causing them to overheat,
selfdestruct, and possibly inflict irreversible damage to the
processor.
The most important aspect of FET performance is
RDS
ON
, which effects regulator efficiency and FET thermal
management requirements.
The power dissipated by the MOSFETs may be estimated
as follows:
Switching MOSFET:
Power
+
ILOAD2
RDSON
duty cycle
Synchronous MOSFET:
Power
+
ILOAD2
RDSON
(1
*
duty cycle)
Duty Cycle =
VOUT
)
(ILOAD
RDSON OF SYNCH FET)
VIN
)
(ILOAD
RDSON OF SYNCH FET)
*
(ILOAD
RDSON OF SWITCH FET)
Off Time Capacitor (C
OFF
)
The C
OFF
timing capacitor sets the regulator off time:
TOFF
+
COFF
4848.5
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17
The preceding equations for duty cycle can also be used
to calculate the regulator switching frequency and select the
C
OFF
timing capacitor:
COFF
+
Perioid
(1
*
duty cycle)
4848.5
where:
Period
+
1
switching frequency
Schottky Diode for Synchronous FET
For synchronous operation, a Schottky diode may be
placed in parallel with the synchronous FET to conduct the
inductor current upon turn off of the switching FET to
improve efficiency. The CS5165A reference circuit does not
use this device due to it's excellent design. Instead, the
body diode of the synchronous FET is utilized to reduce
cost and conducts the inductor current. For a design
operating at 200 kHz or so, the low nonoverlap time
combined with Schottky forward recovery time may make
the benefits of this device not worth the additional expense.
The power dissipation in the synchronous MOSFET due to
body diode conduction can be estimated by the following
equation:
Power
+
VBD
ILOAD
conduction time
switching frequency
Where V
BD
= the forward drop of the MOSFET body
diode. For the CS5165A demonstration board:
Power
+
1.6 V
14.2 A
100 ns
200 kHz
+
0.45 W
This is only 1.1% of the 40 W being delivered to the load.
"Droop" Resistor for Adaptive Voltage Positioning
Adaptive voltage positioning is used to help keep the
output voltage within specification during load transients.
To implement adaptive voltage positioning a "Droop
Resistor" must be connected between the output inductor
and output capacitors and load. This resistor carries the full
load current and should be chosen so that both DC and AC
tolerance limits are met. An embedded PC trace resistor has
the distinct advantage of near zero cost implementation.
However, this droop resistor can vary due to three reasons:
1) the sheet resistivity variation causes the thickness of the
PCB layer to vary. 2) the mismatch of L/W, and 3)
temperature variation.
1. Sheet Resistivity for one ounce copper, the thickness
variation typically 1.15 mil to 1.35 mil. Therefore the
error due to sheet resistivity is:
1.35
*
1.15
1.25
+
16%
2. Mismatch due to L/W. The variation in L/W is
governed by variations due to the PCB manufacturing
process that affect the geometry and the power
dissipation capability of the droop resistor. The error
due to L/W mismatch is typically 1.0%.
3. Thermal Considerations. Due to I
2
R power losses
the surface temperature of the droop resistor will
increase causing the resistance to increase. Also, the
ambient temperature variation will contribute to the
increase of the resistance, according to the formula:
R
+
R20[1
) a
20(T
*
20)]
where:
R
20
= resistance at 20
C
a +
0.00393
C
T = operating temperature
R = desired droop resistor value
For temperature T = 50
C, the % R change = 12%
Droop Resistor Tolerance
Tolerance due to sheet resistivity variation
16%
Tolerance due to L/W error
1.0%
Tolerance due to temperature variation
12%
Total tolerance for droop resistor
29%
In order to determine the droop resistor value the nominal
voltage drop across it at full load has to be calculated. This
voltage drop has to be such that the output voltage full load
is above the minimum DC tolerance spec.
VDROOP(TYP)
+
[VDAC(MIN)
*
VDC(MIN)]
1
)
RDROOP(TOLERANCE)
Example: for a 300 MHz PentiumII, the DC accuracy spec
is 2.74 < V
CC(CORE)
< 2.9 V, and the AC accuracy spec is
2.67 V < V
CC(CORE)
< 2.9 3V. The CS5165A DAC output
voltage is +2.812 V < V
DAC
< +2.868 V. In order not to
exceed the DC accuracy spec, the voltage drop developed
across the resistor must be calculated as follows:
VDROOP(TYP)
+
[VDAC(MIN)
*
VDC PENTIUMII(MIN)]
1
)
RDROOP(TOLERANCE)
+
2.812 V
*
2.74 V
1.3
+
56 mV
With the CS5165A DAC accuracy being 1.0%, the
internal error amplifier's reference voltage is trimmed so
that the output voltage will be 40 mV high at no load. With
no load, there is no DC drop across the resistor, producing
an output voltage tracking the error amplifier output voltage,
including the offset. When the full load current is delivered,
a drop of 56 mV is developed across the resistor. Therefore,
the regulator output is prepositioned at 40 mV above the
nominal output voltage before a load turnon. The total
voltage drop due to a load step is
V40 mV and the
deviation from the nominal output voltage is 40 mV smaller
than it would be if there was no droop resistor. Similarly at
full load the regulator output is prepositioned at 16 mV
below the nominal voltage before a load turnoff. The total
voltage increase due to a load turnoff is
V16 mV and the
deviation from the nominal output voltage is 16 mV smaller
than it would be if there was no droop resistor. This is
because the output capacitors are precharged to value that
is either 40 mV above the nominal output voltage before a
CS5165A
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18
load turnon or, 16 mV below the nominal output voltage
before a load turnoff (see Figure 15).
Obviously, the larger the voltage drop across the droop
resistor ( the larger the resistance), the worse the DC and
load regulation, but the better the AC transient response.
Design Rules for Using a Droop Resistor
The basic equation for laying an embedded resistor is:
RAR
+
L
A
or R
+
L
(W
t)
where:
A = W
t = crosssectional area
= the copper resistivity (
mil)
L = length (mils)
W = width (mils)
t = thickness (mils)
For most PCBs the copper thickness, t, is 35
m (1.37
mils) for one ounce copper.
= 717.86
mil
For a Pentium II load of 14.2 A the resistance needed to
create a 56 mV drop at full load is:
Response Droop
+
56 mV
IOUT
+
56 mV
14.2 A
+
3.9 m
W
The resistivity of the copper will drift with the
temperature according to the following guidelines:
D
R
+
12% @ TA
+ )
50
C
D
R
+
34% @ TA
+ )
100
C
Droop Resistor Width Calculations
The droop resistor must have the ability to handle the load
current and therefore requires a minimum width which is
calculated as follows (assume one ounce copper thickness):
W
+
ILOAD
0.05
where:
W = minimum width (in mils) required for proper power
dissipation, and I
LOAD
Load Current Amps.
The Pentium
II maximum load current is 14.2 A.
Therefore:
W
+
14.2 A
0.05
+
284 mils
+
0.7213 cm
Droop Resistor Length Calculation
L
+
RDROOP
W
t
+
0.0039
284
1.37
717.86
+
2113 mil
+
5.36 cm
Output Inductor
The inductor should be selected based on its inductance,
current capability, and DC resistance. Increasing the
inductor value will decrease output voltage ripple, but
degrade transient response.
Inductor Ripple Current
Ripple Current
+
[(VIN
*
VOUT)
VOUT]
(Switching Frequency
L
VIN)
Example: V
IN
= +5.0 V, V
OUT
= +2.8 V, I
LOAD
= 14.2 A,
L = 1.2
H, Freq = 200 kHz
Ripple Current
+
[(5.0 V
*
2.8 V)
2.8 V]
[200 kHz
1.2
m
H
5.0 V]
+
5.1 A
Output Ripple Voltage
VRIPPLE
+
Inductor Ripple Current
Output Capacitor ESR
Example:
V
IN
= +5.0 V, V
OUT
= +2.8 V, I
LOAD
= 14.2 A, L = 1.2
H,
Switching Frequency = 200 kHz
Output Ripple Voltage = 5.1 A
Output Capacitor ESR
(from manufacturer's specs)
ESR of Output Capacitors to limit Output Voltage Spikes
ESR
+ D
VOUT
D
IOUT
This applies for current spikes that are faster than
regulator response time. Printed Circuit Board resistance
will add to the ESR of the output capacitors.
In order to limit spikes to 100 mV for a 14.2 A Load Step,
ESR = 0.1/14.2 = 0.007
Inductor Peak Current
Peak Current
+
Maximum Load Current
)
Ripple Current
2
Example: V
IN
= +5.0 V, V
OUT
= +2.8 V, I
LOAD
= 14.2 A,
L = 1.2
H, Freq = 200 kHz
Peak Current
+
14.2 A
)
(5.1 2)
+
16.75 A
A key consideration is that the inductor must be able to
deliver the Peak Current at the switching frequency without
saturating.
Response Time to Load Increase
(limited by Inductor value unless Maximum OnTime is
exceeded)
Response Time
+
L
D
IOUT
(VIN
*
VOUT)
Example: V
IN
= +5.0 V, V
OUT
= +2.8 V, L = 1.2
H, 14.2 A
change in Load Current
Response Time
+
1.2
m
H
14.2 A
(5.0 V
*
2.8 V)
+
7.7
m
s
Response Time to Load Decrease
(limited by Inductor value)
Response Time
+
L
Change in IOUT
VOUT
CS5165A
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19
Example: V
OUT
= +2.8 V, 14.2 A change in Load Current,
L = 1.2
H
Response Time
+
1.2
m
H
14.2 A
2.8 V
+
6.1
m
s
Input and Output Capacitors
These components must be selected and placed carefully
to yield optimal results. Capacitors should be chosen to
provide acceptable ripple on the input supply lines and
regulator output voltage. Key specifications for input
capacitors are their ripple rating, while ESR is important for
output capacitors. For best transient response, a combination
of low value/high frequency and bulk capacitors placed
close to the load will be required.
THERMAL MANAGEMENT
Thermal Considerations for Power
MOSFETs and Diodes
In order to maintain good reliability, the junction
temperature of the semiconductor components should be
kept to a maximum of 150
C or lower. The thermal
impedance (junction to ambient) required to meet this
requirement can be calculated as follows:
Thermal Impedance
+
TJUNCTION(MAX)
*
TAMBIENT
Power
A heatsink may be added to TO220 components to
reduce their thermal impedance. A number of PC board
layout techniques such as thermal vias and additional copper
foil area can be used to improve the power handling
capability of surface mount components.
EMI Management
As a consequence of large currents being turned on and off
at high frequency, switching regulators generate noise as a
consequence of their normal operation. When designing for
compliance with EMI/EMC regulations, additional
components may be added to reduce noise emissions. These
components are not required for regulator operation and
experimental results may allow them to be eliminated. The
input filter inductor may not be required because bulk filter
and bypass capacitors, as well as other loads located on the
board will tend to reduce regulator di/dt effects on the circuit
board and input power supply. Placement of the power
component to minimize routing distance will also help to
reduce emissions.
Layout Guidelines
When laying out the CPU buck regulator on a printed
circuit board, the following checklist should be used to
ensure proper operation of the CS5165A.
1. Rapid changes in voltage across parasitic capacitors
and abrupt changes in current in parasitic inductors
are major concerns for a good layout.
2. Keep high currents out of logic grounds.
3. Avoid ground loops as they pick up noise. Use star or
single point grounding. The source of the lower
(synchronous FET) is an ideal point where the input
and output GND planes can be connected.
4. For doublesided PCBs a single large ground plane is
not recommended, since there is little control of
where currents flow and the large surface area can act
as an antenna.
5. Even though double sided PCBs are usually sufficient
for a good layout, fourlayer PCBs are the optimum
approach to reducing susceptibility to noise. Use the
two internal layers as the +5.0 V and GND planes, and
the top and bottom layers for the vias.
6. Keep the inductor switching node small by placing
the output inductor, switching and synchronous FETs
close together.
7. The FET gate traces to the IC must be as short,
straight, and wide as possible. Ideally, the IC has to be
placed right next to the FETs.
8. Use fewer, but larger output capacitors, keep the
capacitors clustered, and use multiple layer traces
with heavy copper to keep the parasitic resistance
low.
9. Place the switching FET as close to the +5.0 V input
capacitors as possible.
10. Place the output capacitors as close to the load as
possible.
11. Place the V
FB
filter resistor in series with theV
FB
pin
(pin 16) right at the pin.
12. Place the V
FB
filter capacitor right at the V
FB
pin (pin
16).
13. The "Droop" Resistor (embedded PCB trace) has to
be wide enough to carry the full load current.
14. Place the V
CC
bypass capacitor as close as possible to
the V
CC
pin.
CS5165A
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20
+
COMP
ENABLE
V
FB
V
GATE(H)
V
GATE(L)
PWRGD
V
CC
V
ID0
V
ID1
V
ID2
V
ID3
V
ID4
PGND
SS
C
OFF
CS5165A
6.0 m
330 pF
LGND
1200
F/10 V
3
1.2
H
Si4410DY
1.0
F
3.3 k
0.1
F
1000 pF
5.0 V
MBRS120
1200
F/10 V
5
Figure 28. Additional Application Diagram, +5.0 V to +2.8 V @ 14.2 A for 300 MHz Pentium II
PENTIUM II
SYSTEM
Droop Resistor
(Embedded PCB trace)
0.1
F
Si9410DY
MBRS120
MBRS120
1.0
F
ENABLE
PWRGD
V
ID0
V
ID1
V
ID2
V
ID3
V
ID4
V
CC
V
SS
CS5165A
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21
PACKAGE DIMENSIONS
SO16L
DW SUFFIX
CASE 751G03
ISSUE B
D
14X
B
16X
SEATING
PLANE
S
A
M
0.25
B
S
T
16
9
8
1
h
X 45
_
M
B
M
0.25
H
8X
E
B
A
e
T
A1
A
L
C
q
NOTES:
1. DIMENSIONS ARE IN MILLIMETERS.
2. INTERPRET DIMENSIONS AND TOLERANCES
PER ASME Y14.5M, 1994.
3. DIMENSIONS D AND E DO NOT INLCUDE MOLD
PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 PER SIDE.
5. DIMENSION B DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.13 TOTAL IN EXCESS
OF THE B DIMENSION AT MAXIMUM MATERIAL
CONDITION.
DIM
MIN
MAX
MILLIMETERS
A
2.35
2.65
A1
0.10
0.25
B
0.35
0.49
C
0.23
0.32
D
10.15
10.45
E
7.40
7.60
e
1.27 BSC
H
10.05
10.55
h
0.25
0.75
L
0.50
0.90
q
0
7
_
_
PACKAGE THERMAL DATA
Parameter
SO16L
Unit
R
JC
Typical
23
C/W
R
JA
Typical
105
C/W
CS5165A
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22
Notes
CS5165A
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23
Notes
CS5165A
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24
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V
2
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