Preliminary
RT9226B
DS9226B-01 May 2001
www.richtek.com
1
Synchronous PWM Step-down DC/DC Converter Controller
General Description
The RT9226B is a low cost, high-efficiency voltage-
mode PWM controller for motherboard power supply
application. Synchronous N-channel MOSFET driver,
short-circuit protection, and soft start function are
integrated in a single chip. A simple high power buck
regulator with shutdown function can be
implemented with minimum external components.
The RT9226B provides current-limit protection by
monitoring the voltage drop across N-channel
MOSFET in over current condition, therefore,
eliminates the current sensing resistor and minimizes
the efficiency loss. The soft start function reduces the
stress on power supply and components in power on
duration. The 200 kHz operating frequency and high
speed PWM control loop with Synchronous N-
channel MOSFET driver provide optimized
compromise between efficiency, cost, and response
speed. Other features include output voltage
monitoring for power good indication and over
voltage protection.
Ordering Information
RT9226B
Features
Synchronous N-channel MOSFET Driver
High Efficiency
Fast Response with 200kHz Operating Frequency
Adjustable Current Limit by Sensing MOSFET
R
DS(ON)
, without Extra Current Sensing Resistor
Shutdown Function
Power Good Indication Output and Over-voltage
Protection
Applications
Low Cost CPU Power Supply
Motherboard I/O Power Supply
Add-On Card Power Supply
DDR SDRAM Bus Terminator Power Supply
Pin Configurations
Part Number
Pin Configurations
RT9226BCS
(Plastic SOP-14)
TOP VIEW
Operating temperature range
C: Commercial standard
Package type
S : SOP-14
1
2
3
4
5
6
7
VSEN
OCSET
SS
FB
EN
GND
PGNDH
VCC
LGATE
PGNDL
BOOT
UGATE
PHASE
PGOOD
14
13
12
11
10
9
8
RT9226B
Preliminary
www.richtek.com
DS9226B-01 May 2001
2
Absolute Maximum Ratings
Supply Voltage
15V
Input, Output or I/O Voltage
GND0.3V to Vcc+0.3V
Ambient Temperature Range
0
C to 70
C
Operating Junction Temperature Range
0
C to 125
C
Storage Temperature Range
-
65
C to 150
C
Package Thermal Resistance
SOP-14,
JA
160
C/W
Lead Temperature (Soldering, 10 sec.)
300
C
Electrical Characteristics
(VCC
= 12V, GND = 0V, T
A
= 25
C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
VCC Supply Current
Nominal Supply Current
I
CC
UGATE Open
--
3
--
mA
Power-On Reset
VCC Rising Threshold
V
OCSET
= 4.5V
--
9.5
--
V
VCC Falling Threshold
V
OCSET
= 4.5V
--
7.5
--
V
Enable Input Threshold
V
EN
0.2
--
2.2
V
Oscillator
Frequency
170
200
230
KHz
Ramp Amplitude
V
OSC
--
1.9
--
V
Internal Voltage Reference
Reference Voltage
V
REF
0.785
0.800
0.815
V
PWM Controller Error Amplifier
DC Gain
--
65
--
dB
PWM Controller Gate Driver
UGATE Source
R
UGATE
I
UGATE
= 0.3A
--
8
--
UGATE Sink
R
UGATE
I
UGATE
= 0.3A
--
6
--
LGATE Source
I
LGATE
V
CC
= 12V, V
LGATE
= 6V
--
500
--
mA
LGATE Sink
R
LGATE
I
LGATE
= 1V
--
5
--
Protection
OCSET Current Source
I
OCSET
V
OCSET
= 4.5V
170
200
230
A
Soft-start Current
I
SS
V
SS
= 1.5V
--
10
--
A
Over-voltage Trip (VSEN/VREF)
--
115
120
%
Power Good
Upper Threshold (VSEN/VREF)
--
108
--
%
Lower Threshold (VSEN/VREF)
--
92
--
%
PGOOD Voltage Low
V
PGOOD
I
PGOOD
= -5mA
--
0.5
--
V
Preliminary
RT9226B
DS9226B-01 May 2001
www.richtek.com
3
Function Block Diagram
Pin Description
Pin No.
Pin Name
Pin Function
1
VSEN
Output Voltage Monitoring Input
2
OCSET
Current Limit Set Pin with 200
A Current Sink
3
SS
Soft Start, connect a capacitor from this pin to GND
4
FB
Feedback Input Pin
5
EN
Regulator Enable with Low Shutdown
6
GND
Ground
7
PGNDH
High Side Drive GND
8
PGOOD
Power Good Indication Output
9
PHASE
Current Limit Sense Input
10
UGATE
High Side Driver Output
11
BOOT
Driver Power
12
PGNDL
Low Side Driver GND
13
LGATE
Low Side Driver Output
14
VCC
Power Supply Input
Soft
Start
Power-on
Reset
Control
Logic
Oscillator
Vref
10
A
4.5V
Error
Amp
PWM
Comparator
200
A
SS
EN
FB
PGOOD
VCC
OCSET
PHASE
BOOT
UGATE
PGNDH
GND
Output
Voltage
Monitor
VSEN
47K
Gate
Control
Logic
V
CC
LGATE
PGNDL
Over Current
Comparator
+
_
+
_
+
_
+
RT9226B
Preliminary
www.richtek.com
DS9226B-01 May 2001
4
Typical Application Circuit
C4, C5: Each 1000
F 6.3WV DC, Sanyo MV-GX or Equivalent.
L1: Core: Micrometals T50-52; Winding: 5 turns of 18 AWG.
L2: Core: Micrometals T60-52; Winding: 14 turns of 17 AWG.
Q1, Q2: PHB83N03LT, PHB95N03LT
EN
SS
PGNDL
FB
LGATE
UGATE
OCSET
5
3
12
2
10
13
4
RT9226B
11
8
14 VCC
PGOOD
BOOT
V
IN
5V
V
OUT
1.25V/10A
12V
L1
1
H
L2
7
H
R2
2.4k
C2
1000pF
C4
1000
F
2
D2
1N5817
Q1
Q2
R5
10K 1%
C3
0.1
F
D1
15V
C1
1
F
R1
10
Low Shutdown
GND
6
PGNDH
7
Power Good
9
1
+
-
C5
1000
F
6
+
-
C6
1
F
R3
510 1%
R4
910 1%
PHASE
VSEN
Preliminary
RT9226B
DS9226B-01 May 2001
www.richtek.com
5
Package Information
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
8.534
8.738
0.336
0.344
B
3.810
3.988
0.150
0.157
C
1.346
1.753
0.053
0.069
D
0.330
0.508
0.013
0.020
F
1.194
1.346
0.047
0.053
H
0.178
0.254
0.007
0.010
I
0.102
0.254
0.004
0.010
J
5.791
6.198
0.228
0.244
M
0.406
1.270
0.016
0.050
B
M
H
B
J
A
C
I
F
D
RT9226B
Preliminary
www.richtek.com
DS9226B-01 May 2001
6
RICHTEK TECHNOLOGY CORP.
Headquarter
5F, No. 20, Taiyuen Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
RICHTEK TECHNOLOGY CORP.
Taipei Office (Marketing)
8F-1, No. 137, Lane 235, Paochiao Road, Hsintien City
Taipei County, Taiwan, R.O.C.
Tel: (8862)89191466 Fax: (8862)89191465
Email: marketing@richtek.com
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