Description
GM38C4x is fixed frequency, high performance, and cur-
rent- mode PWM controllers. Gamma's BiCMOS devices
are pin compatible with standard 384x bipolar devices but
with several improvements.
Undervoltage lockout circuitry allows the '42 and '44 ver-
sions 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 16V.
When compared to bipolar 384x devices operating from a
15V supply, start-up current has been reduced to 50µA typi-
cal and operating current has been reduced to 4.0 mA typi-
cal. Decreased output rise/fall times drive larger MOSFETs,
and rail-to-rail output capability increases efficiency, espe-
cially at lower supply voltages. GM38C4x also features a
trimmed oscillator discharge current and bandgap refer-
ence.
GM38C4x denotes 8-pin plastic DIP and SOP packages.
Features
40ns output rise and 30ns output fall times
-40
°
to +85
°
C temp. range same as standard
UC284x
Low-power BiCMOS Process
Very low start-up current (50µA typical)
Low operating current (4mA typical)
CMOS outputs with rail-to-rail swing
500kHz current-mode operation
Pin-for-pin compatible with UC3842/ 3843
/ 3844/ 3845(A)
Trimmed oscillator discharge current
UVLO with hysteresis
Low cross-conduction currents
Application
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
GM38C42, GM38C43, GM38C44, GM38C45
1
www.gammamicro.com
GM 431
V0.1
MARKING INFORMATION & PIN CONFIGURATIONS
(TOP VIEW)
SOP - 8
V
DD
V
REF
8 7 6 5
OUT
GND
DIP - 8
V
DD
V
REF
8 7 6 5
GM38CXX
AYWW
OUT
GND
GM38CXX
AYWW
1 2 3 4
COMP
FB
R
T
/ C
T
I
SNS
COMP
FB
1 2 3 4
R
T
/ C
T
I
SNS
A
= Assembly Location
Y
= Year
W W = Weekly
GM38C42, GM38C43, GM38C44, GM38C45
ORDERING INFORMATION
Ordering Number
GM38C42S8T
GM38C42S8R
GM38C42D8T
GM38C43S8T
GM38C43S8R
GM38C43D8T
GM38C44S8T
GM38C44S8R
GM38C44D8T
GM38C45S8T
GM38C45S8R
GM38C45D8T
Package
SOP - 8
SOP - 8
DIP-8
SOP - 8
SOP - 8
DIP-8
SOP - 8
SOP - 8
DIP-8
SOP - 8
SOP - 8
DIP-8
Shipping
100 Units/ Tube
2,500 Units/ Tape & Reel
60 Units/ Tube
100 Units/ Tube
2,500 Units/ Tape & Reel
60 Units/ Tube
100 Units/ Tube
2,500 Units/ Tape & Reel
60 Units/ Tube
100 Units/ Tube
2,500 Units/ Tape & Reel
60 Units/ Tube
* For detail Ordering Number identification, please see last page.
2
ABSOLUTE MAXIMUM RATINGS
PARAMETER
Zener Current
Operation at 16V may require special precautions(Note6)
Supply Voltage(Note 6)
Switch Supply Voltage
Current Sense Voltage
Feedback Voltage
Output Current
Storage Temperature
SYMBOL
I
DD
V
DD
V
D
V
ISNS
V
FB
I
OUT
T
A
VALUE
30
18
18
- 0.3 to + 5.5
- 0.3 to + 5.5
0.5
- 50 to + 150
UNIT
mA
V
V
V
V
A
°C
OPERATING RATINGS
PARAMETER
Junction Temperature
SYMBOL
T
J
VALUE
150
UNIT
°C
PACKAGE PIN DESCRIPTION
Compensation: Connect external Compensation network to modify the error amplifier
output.
Feedback (Input): Error amplifier input .Feedback is 2.5Vat desired output voltage.
Current Sense (Input): Current sense comparator input. Connect to current sensing
resistor or current transformer.
Timing Resistor / Timing Capacitor: Connect external RC network to select switching
frequency.
Ground: Combined analog and power ground.
Power Output: Totem - pole output.
Analog Supply (Input): Controller circuitry supply input. Return to analog ground (AGND).
5V Reference (Output): Connect external RC network.
1
2
3
4
5
6
7
8
COMP
FB
I
SNS
R
T
/ C
T
GND
OUT
V
DD
V
REF
BLOCK DIAGRAM
V
DD
7
35V
5V
Reference
UVLO
*
V
REF
8
R
T
/ C
T
4
Oscillator
T
Q
OUTPUT
6
FB
2
-
2R
R
2.5V
+
-
+
-
+
S
R Q
*
COMP
1
GND*
5
I
SNS
3
* 8 - lead versions only
GM38C42, GM38C43, GM38C44, GM38C45
3
PIN LEAD
FUNCTION
FUNCTION
Power Management
ELECTRICAL CHARACTERISTICS
(T
A
= -40°C to 85°C, Note 4, V
DD
= 15V, C
T
=3.3 nF, R
T
=10kW, unless otherwise noted )
CHARACTERISTICS
Reference Section
Output Voltage
Line Regulation
Load Regulation
Temp. Stability
Total Output Variation
Output Noise Voltage
Long Term Stability
Output Short Circuit
TEST CONDITIONS
MIN
TYP
MAX
UNIT
T
A
= 25°C, I
O
= 1mA
12V
V
DD
1
16V, I
O
= 5µA, (Note 6)
I
O
20mA
4.9
5.0
2
1
0.2
5.1
20
25
V
mV
mV
mV / °C
(Note 1)
Line, Load, Temp.,Note 1
10Hz
f
10kHz, T
A
= 25°C, (Note 1)
4.82
5.18
50
5
25
-180
V
µV
mV
mA
T
A
= 125°C, 1000hrs., (Note 1)
-30
-80
Oscillator Section
Initial Accuracy
Voltage Stability
Temp. Stability
Clock Ramp
Reset Current
Amplitude
T
A
= 25°C, (Note 5)
12
T
MIN
V
DD
T
A
16V, (Note 6)
T
MAX
, (Note 1)
49
52
0.2
0.04
55
1.0
KHz
%
% / °C
T
A
= 25°C, V
RT/CT
= 2V,
T
MIN
T
A
T
MAX
V
RT/CT
(Peak to Peak)
7.7
7.2
8.4
8.4
1.9
9.0
9.5
mA
Vp-p
GM38C42, GM38C43, GM38C44, GM38C45
Error Amplifier Section
Input Current
Input Voltage
Open Loop Voltage Gain
Power Supply Rejection Ratio
Output Sink Current
Output Source Current
High Output Voltage
Low Output Voltage
Unity Gain Bandwidth
V
FB
= 5V
V
COMP
= 2.5V
2V
12V
V
O
V
DD
4V
16V
2.42
65
60
2
-0.5
5.0
-0.1
2.5
90
-2
2.58
µA
V
dB
dB
V
FB
= 2.7V, V
COMP
= 1.1V
V
FB
= 2.3V, V
COMP
= 5V
V
FB
= 2.3V, R
L
= 15k to GND
V
FB
= 2.7V, R
L
= 15k to V
REF
(Note 1)
14
-1
6.6
0.1
1.1
mA
mA
V
V
MHz
0.7
1.0
Current Sense Section
Gain
Maximum Threshold
PSRR
Input Bias Current
Delay to Output
Note 2 and 3
V
COMP
= 5V, (Note 2)
12V
V
DD
16V, (Note 2)
2.85
0.9
3.0
1.0
70
-1.0
120
3.15
1.1
V/V
V
dB
-2
250
µA
ns
4
ELECTRICAL CHARACTERISTICS
(T
A
= -40°C to 85°C, Note 4, V
DD
= 15V, C
T
=3.3 nF, R
T
=11kW, unless otherwise noted )
CHARACTERISTICS
Output Section
R
DS(ON)
High
R
DS(ON)
Low
Rise Time
Fall Time
Undervoltage Lockout Section
GM38C42, GM38C44
Start Threshold
GM38C43, GM38C45
GM38C42, GM38C44
Minimum Operating Voltage
GM38C43, GM38C45
PWM Section
Maximum Duty Cycle
Minimum Duty Cycle
Total Standby Current
µA
mA
V
GM38C42, GM38C43
GM38C44, GM38C45
94
46
96
50
0
%
%
7.0
7.6
8.2
13.5
7.8
8
14.5
8.4
9
15.5
9.0
10
V
V
I
SOURCE
= 200mA
I
SINK
= 200mA
T
A
= 25°C, C
L
= 1nF
T
A
= 25°C, C
L
= 1nF
20
W
11
40
30
80
60
ns
ns
TEST CONDITIONS
MIN
TYP
MAX
UNIT
V
DD
= 7.5V for GM38C43, GM38C45
Operating Supply Current
Zener Voltage (V
DD
)
V
FB
= V
ISNS
= 0V
I
DD
= 25 mA, Note 6
30
4
37
6
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:
A=
DV
PIN1
;0
V
TH
(I
SNS
)
V
TH
(I
SNS
)
0.8V
Note 4:
Adjust V
DD
above the start threshold before setting at 15V.
Note 5:
Output frequency equals oscillator frequency for the GM38C42 and GM38C43. Output frequency for the
GM38C44, and GM38C45 equals one half the oscillator frequency.
Note 6:
On 8-pin version, 18V is maximum input on pin 7, as this is also the supply pin for the output stage.
GM38C42, GM38C43, GM38C44, GM38C45
5
Start - Up Current
V
DD
= 13V for GM38C42, GM38C44
50
200
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