MIC38C42/3/4/5
Micrel, Inc.
July 2005
1
M9999-072805
MIC38C42/3/4/5
BiCMOS Current-Mode PWM Controllers
General Description
The MIC38C4x are fixed frequency, high performance, cur-
rent-mode PWM controllers. Micrel's BiCMOS devices are
pin compatible with 384x bipolar devices but feature several
improvements.
Undervoltage lockout circuitry allows the '42 and '44 versions
to start up at 14.5V and operate down to 9V, and the '43 and
'45 versions start at 8.4V with operation down to 7.6V. All
versions operate up to 20V.
When compared to bipolar 384x devices operating from a 15V
supply, start-up current has been reduced to 50A typical and
operating current has been reduced to 4.0 mA typical. De-
creased output rise and fall times drive larger MOSFETs, and
rail-to-rail output capability increases efficiency, especially at
lower supply voltages. The MIC38C4x also features a trimmed
oscillator discharge current and bandgap reference.
The MIC38C4x denotes 8-pin plastic DIP and SOIC packages.
MIC384Cx-1 denotes 14-pin plastic DIP and SOIC packages.
8-pin devices feature small size, while 14-pin devices separate
the analog and power connections for improved perfomance
and power dissipation.
For fast rise and fall times and higher output drive, refer to
the MIC38HC4x.
Functional Diagram
Features
Fast 40ns output rise and 30ns output fall times
40C to +85C temperature range
meets UC284x specifications
High-performance, low-power BiCMOS Process
Ultralow start-up current (50A typical)
Low operating current (4mA typical)
CMOS outputs with rail-to-rail swing
500kHz current-mode operation
Trimmed 5V bandgap reference
Pin-for-pin compatible with UC3842/3843/3844/3845(A)
Trimmed oscillator discharge current
UVLO with hysteresis
Low cross-conduction currents
Applications
Current-mode, off-line, switched-mode power supplies
Current-mode, dc-to-dc converters.
Step-down "buck" regulators
Step-up "boost" regulators
Flyback, isolated regulators
Forward converters
Synchronous FET converters
T Q
S
R Q
R
2R
Oscillator
UVLO
5V
Reference
VDD
7 (12)
VREF
8 (14)
RT/CT
4 (7)
FB
2 (3)
2.5V
COMP
1 (1)
GND* (AGND)
5 (9)
ISNS
3 (5)
OUT
6 (10)
( )
pins are on MIC38C4x-1 (14-lead) versions only
*
MIC38C4x, (8-lead) versions only
(VD)
(11)
(PGND)
(8)
35V
*
*
MIC38C42, MIC38C43 (96% max. duty cycle) versions only
MIC38C44, MIC38C45 (50% max. duty cycle) versions only
MM8 is a trademark of Micrel, Inc.
Micrel, Inc. 2180 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 http://www.micrel.com
MIC38C42/3/4/5
Micrel, Inc.
July 2005
3
M9999-072805
Pin Description
Pin Number Pin Number
Pin Name
Pin Function
N, M, MM
-1BN, -1BM
1
1
COMP
Compensation: Connect external compensation network to modify the error
amplifier output.
2
NC
Not internally connected.
2
3
FB
Feedback (Input): Error amplifier input. Feedback is 2.5V at desired output
voltage.
4
NC
Not internally connected.
3
5
ISNS
Current Sense (Input): Current sense comparator input. Connect to current
sensing resistor or current transformer.
6
NC
Not internally connected.
4
7
RT/CT
Timing Resistor/Timing Capacitor: Connect external RC network to select
switching frequency.
5
GND
Ground: Combined analog and power ground.
8
PGND
Power Ground: N-channel driver transistor ground.
9
AGND
Analog Ground: Controller circuitry ground.
6
10
OUT
Power Output: Totem-pole output.
11
VD
Power Supply (Input): P-channel driver transistor supply input. Return to
power ground (PGND).
7
12
VDD
Analog Supply (Input): Controller circuitry supply input. Return to analog
ground (AGND).
13
NC
Not internally connected.
8
14
VREF
5V Reference (Output): Connect external RC network.
1
2
3
4
8
7
6
5
COMP
FB
ISNS
RT/CT
VREF
VDD
OUT
GND
MIC38C4x
2
NC
NC
13
3
FB
VDD
12
4
NC
VD
11
5
ISNS
OUT
10
6
NC
AGND
9
7
RT/CT
PGND
8
1
COMP
V R E F
14
MIC38C4x-1
8-Pin DIP (N)
8-Lead SOIC (M)
8-Lead MM8TM (MM)
14-Pin DIP (-1BN)
14-Lead SOIC (-1BM)
Pin Configuration
MIC38C42/3/4/5
Micrel, Inc.
M9999-072805
4
July 2005
Electrical Characteristics
V
DD
= 15V,
Note 4; R
T
= 11.0k; C
T
= 3.3nF; 40C T
A
85C; unless noted
Parameter
Test Conditions
Min
Typ
Max
Units
Reference Section
Output Voltage
T
A
= 25C, I
O
= 1mA
4.90
5.00
5.10
V
Line Regulation
12V V
DD
18V, I
O
= 5A,
Note 6
2
20
mV
Load Regulation
1 I
O
20mA
1
25
mV
Temp. Stability
Note 1
0.2
mV/C
Total Output Variation
Line, Load, Temp.,
Note 1
4.82
5.18
V
Output Noise Voltage
10Hz f 10kHz, T
A
= 25C,
Note 1
50
V
Long Term Stability
T
A
= 125C, 1000 hrs.,
Note 1
5
25
mV
Output Short Circuit
30
80
180
mA
Oscillator Section
Initial Accuracy
T
A
= 25C,
Note 5
49
52
55
kHz
Voltage Stability
12 V
DD
18V,
Note 6
0.2
1.0
%
Temp. Stability
T
MIN
T
A
T
MAX
,
Note 1
0.04
%/C
Clock Ramp
T
A
= 25C, V
RT/CT
= 2V
7.7
8.4
9.0
mA
Reset Current
T
A
= T
MIN
to T
MAX
7.2
8.4
9.5
mA
Amplitude
V
RT/CT
peak to peak
1.9
Vp-p
Error Amp Section
Input Voltage
V
COMP
= 2.5V
2.42
2.50
2.58
V
Input Bias Current
V
FB
= 5.0V
0.1
2
A
A
VOL
2 V
O
4V
65
90
dB
Unity Gain Bandwidth
Note 1
0.7
1.0
MHz
PSRR
12 V
DD
18V
60
dB
Output Sink Current
V
FB
= 2.7V, V
COMP
= 1.1V
2
14
mA
Output Source Current
V
FB
= 2.3V, V
COMP
= 5V
0.5
1
mA
V
OUT
High
V
FB
= 2.3V, R
L
= 15k to ground
5
6.8
V
V
OUT
Low
V
FB
= 2.7V, R
L
= 15k to V
REF
0.1
1.1
V
Absolute Maximum Ratings
Zener Current (V
DD
) ................................................... 30mA
Operation at 18V may require
special precautions (Note 6).
Supply Voltage (V
DD
),
Note 6 ........................................20V
Switch Supply Voltage (V
D
) ...........................................20V
Current Sense Voltage (V
ISNS
) .......................0.3V to 5.5V
Feedback Voltage (V
FB
) .................................0.3V to 5.5V
Output Current, 38C42/3/4/5 (I
OUT
) ............................. 0.5A
Storage Temperature (T
A
) ......................... 65C to +150C
Operating Ratings
Junction Temperature (T
J
) ......................................... 150C
Package Thermal Resistance
8-Pin Plastic DIP (
JA
) .......................................125C/W
8-Pin MM8TM (
JA
) .............................................250C/W
8-Pin SOIC (
JA
) ................................................170C/W
14-Pin Plastic DIP (
JA
) ......................................90C/W
14-Pin SOIC (
JA
) ..............................................145C/W
MIC38C42/3/4/5
Micrel, Inc.
July 2005
5
M9999-072805
Parameter
Test Conditions
Min
Typ
Max
Units
Current Sense
Gain
Notes 2, 3
2.85
3.0
3.15
V/V
MaximumThreshold
V
COMP
= 5V,
Note 2
0.9
1
1.1
V
PSRR
12 V
DD
18V,
Note 2
70
dB
Input Bias Current
0.1
2
A
Delay to Output
120
250
ns
Output
R
DS(ON)
High
I
SOURCE
= 200mA
20
R
DS(ON)
Low
I
SINK
= 200mA
11
Rise Time
T
A
= 25C, C
L
= 1nF
40
80
ns
Fall Time
T
A
= 25C, C
L
= 1nF
30
60
ns
Undervoltage Lockout
Start Threshold
MIC38C42/4
13.5
14.5
15.5
V
MIC38C43/5
7.8
8.4
9.0
V
Minimum Operating Voltage
MIC38C42/4
8
9
10
V
MIC38C43/5
7.0
7.6
8.2
V
Pulse Width Modulator
Maximum Duty Cycle
MIC38C42/3
94
96
%
MIC38C44/5
46
50
%
Minimum Duty Cycle
0
%
Total Standby Current
Start-Up Current
V
DD
= 13V for MIC38C42/44
50
200
A
V
DD
= 7.5V for MIC38C43/45
Operating Supply Current
V
FB
= V
ISNS
= 0V
4.0
6.0
mA
Zener Voltage (V
DD
)
I
DD
= 25mA,
Note 6
30
37
V
Note 1: These parameters, although guaranteed, are not 100% tested in production.
Note 2: Parameter measured at trip point of latch with V
EA
= 0.
Note 3: Gain defined as:
V
PIN1
A =
; 0 V
TH
(I
SNS
) 0.8V
V
TH
(I
SNS
)
Note 4: Adjust V
DD
above the start threshold before setting at 15V.
Note 5: Output frequency equals oscillator frequency for the MIC38C42 and MIC38C43. Output frequency for the MIC38C44, and
MIC38C45 equals one half the oscillator frequency.
Note 6: On 8-pin version, 20V is maximum input on pin 7, as this is also the supply pin for the output stage. On 14-pin version, 40V is
maximum for pin 12 and 20V maximum for pin 11.
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