GAMMA GM38C42

Description
GM38C4x is fixed frequency, high performance, and cur-
Features
40ns output rise and 30ns output fall times
rent- mode PWM controllers. Gamma's BiCMOS devices
-40° to +85°C temp. range same as standard
are pin compatible with standard 384x bipolar devices but
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
with 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 16V.
When compared to bipolar 384x devices operating from a
15V supply, start-up current has been reduced to 50µA typical and operating current has been reduced to 4.0 mA typical. Decreased output rise/fall times drive larger MOSFETs,
and rail-to-rail output capability increases efficiency, especially at lower supply voltages. GM38C4x also features a
trimmed oscillator discharge current and bandgap reference.
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
GM 431
www.gammamicro.com
1
V0.1
Application
GM38C42, GM38C43, GM38C44, GM38C45
GM38C4x denotes 8-pin plastic DIP and SOP packages.
MARKING INFORMATION & PIN CONFIGURATIONS (TOP VIEW)
SOP - 8
VDD
VREF
DIP - 8
VDD
VREF
OUT
GND
8 7 6 5
8 7 6 5
GM38CXX
GM38CXX
AYWW
AYWW
1 2 3 4
COMP
FB
OUT
GND
1 2 3 4
RT / C T
ISNS
RT / C T
ISNS
COMP
FB
GM38C42, GM38C43, GM38C44, GM38C45
A
= Assembly Location
Y
= Year
W W = Weekly
2
ORDERING INFORMATION
Ordering Number
Package
GM38C42S8T
SOP - 8
100 Units/ Tube
GM38C42S8R
SOP - 8
2,500 Units/ Tape & Reel
GM38C42D8T
DIP-8
60 Units/ Tube
GM38C43S8T
SOP - 8
100 Units/ Tube
GM38C43S8R
SOP - 8
2,500 Units/ Tape & Reel
GM38C43D8T
DIP-8
60 Units/ Tube
GM38C44S8T
SOP - 8
100 Units/ Tube
GM38C44S8R
SOP - 8
2,500 Units/ Tape & Reel
GM38C44D8T
DIP-8
60 Units/ Tube
GM38C45S8T
SOP - 8
100 Units/ Tube
GM38C45S8R
SOP - 8
2,500 Units/ Tape & Reel
GM38C45D8T
DIP-8
60 Units/ Tube
* For detail Ordering Number identification, please see last page.
Shipping
ABSOLUTE MAXIMUM RATINGS
SYMBOL
VALUE
UNIT
Zener Current
Operation at 16V may require special precautions(Note6)
IDD
30
mA
Supply Voltage(Note 6)
VDD
18
V
Switch Supply Voltage
VD
18
V
Current Sense Voltage
PARAMETER
VISNS
- 0.3 to + 5.5
V
Feedback Voltage
VFB
- 0.3 to + 5.5
V
Output Current
IOUT
0.5
A
TA
- 50 to + 150
°C
SYMBOL
TJ
VALUE
UNIT
150
°C
Storage Temperature
OPERATING RATINGS
PARAMETER
Junction Temperature
PIN LEAD
FUNCTION
FUNCTION
Compensation: Connect external Compensation network to modify the error amplifier
output.
1
COMP
2
FB
Feedback (Input): Error amplifier input .Feedback is 2.5Vat desired output voltage.
3
ISNS
4
RT / C T
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.
5
GND
Ground: Combined analog and power ground.
6
OUT
Power Output: Totem - pole output.
7
VDD
Analog Supply (Input): Controller circuitry supply input. Return to analog ground (AGND).
8
VREF
5V Reference (Output): Connect external RC network.
BLOCK DIAGRAM
VDD
*
35V
7
5V
Reference
VREF
8
RT / C T
UVLO
Oscillator
4
OUTPUT
6
T
FB
2
2R
-
2.5V
+
+
Q
S
R Q
R
+
-
*
COMP
1
GND*
5
GM38C42, GM38C43, GM38C44, GM38C45
PACKAGE PIN DESCRIPTION
3
ISNS
3
* 8 - lead versions only
Power Management
ELECTRICAL CHARACTERISTICS
(TA = -40°C to 85°C, Note 4, VDD = 15V, CT=3.3 nF, RT=10kW, unless otherwise noted )
CHARACTERISTICS
TEST CONDITIONS
MIN
TYP
MAX
UNIT
TA = 25°C, IO = 1mA
4.9
5.0
5.1
V
2
20
mV
1
25
mV
Reference Section
Output Voltage
Line Regulation
12V
VDD
16V, IO = 5µA, (Note 6)
1
Load Regulation
IO
Long Term Stability
0.2
Line, Load, Temp.,Note 1
Total Output Variation
Output Noise Voltage
20mA
(Note 1)
Temp. Stability
10Hz
f
4.82
10kHz, TA = 25°C, (Note 1)
V
µV
50
TA = 125°C, 1000hrs., (Note 1)
Output Short Circuit
mV / °C
5.18
5
25
mV
-30
-80
-180
mA
49
52
55
KHz
1.0
%
Oscillator Section
Initial Accuracy
Voltage Stability
12
Temp. Stability
TMIN
Clock Ramp
Reset Current
GM38C42, GM38C43, GM38C44, GM38C45
VDD
16V, (Note 6)
0.2
TA
TMAX, (Note 1)
0.04
TA = 25°C, VRT/CT = 2V,
TMIN TA TMAX
% / °C
7.7
8.4
9.0
7.2
8.4
9.5
VRT/CT (Peak to Peak)
1.9
Input Current
VFB = 5V
-0.1
-2
Input Voltage
VCOMP = 2.5V
2.42
2.5
2.58
Open Loop Voltage Gain
2V
VO
4V
65
90
12V
VDD
16V
60
Amplitude
4
TA = 25°C, (Note 5)
mA
Vp-p
Error Amplifier Section
Power Supply Rejection Ratio
Output Sink Current
V
dB
dB
VFB = 2.7V, VCOMP = 1.1V
2
14
mA
mA
VFB = 2.3V, VCOMP = 5V
-0.5
-1
High Output Voltage
VFB = 2.3V, RL = 15k to GND
5.0
6.6
Low Output Voltage
VFB = 2.7V, RL = 15k to VREF
Output Source Current
µA
Unity Gain Bandwidth
0.1
V
1.1
(Note 1)
0.7
1.0
Note 2 and 3
2.85
3.0
3.15
VCOMP = 5V, (Note 2)
0.9
1.0
1.1
V
MHz
Current Sense Section
Gain
Maximum Threshold
PSRR
12V
VDD
16V, (Note 2)
70
V/V
V
dB
Input Bias Current
-1.0
-2
µA
Delay to Output
120
250
ns
ELECTRICAL CHARACTERISTICS
(TA = -40°C to 85°C, Note 4, VDD = 15V, CT=3.3 nF, RT=11kW, unless otherwise noted )
CHARACTERISTICS
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Output Section
RDS(ON) High
ISOURCE = 200mA
20
RDS(ON) Low
ISINK = 200mA
11
Rise Time
TA = 25°C, CL = 1nF
40
80
ns
Fall Time
TA = 25°C, CL = 1nF
30
60
ns
W
Undervoltage Lockout Section
GM38C42, GM38C44
13.5
14.5
15.5
GM38C43, GM38C45
7.8
8.4
9.0
GM38C42, GM38C44
8
9
10
GM38C43, GM38C45
7.0
7.6
8.2
GM38C42, GM38C43
94
96
GM38C44, GM38C45
46
50
Start Threshold
Minimum Operating Voltage
V
V
PWM Section
Maximum Duty Cycle
Minimum Duty Cycle
%
0
%
Start - Up Current
VDD = 13V for GM38C42, GM38C44
50
200
VDD = 7.5V for GM38C43, GM38C45
VFB = VISNS = 0V
Operating Supply Current
Zener Voltage (VDD)
IDD = 25 mA, Note 6
4
30
37
6
µA
mA
V
Note 1: These parameters, although guaranteed, are not 100% tested in production.
Note 2: Parameter measured at trip point of latch with VEA = 0.
Note 3: Gain defined as:
A=
DVPIN1
;0
VTH (ISNS)
VTH (ISNS)
0.8V
Note 4: Adjust VDD 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
Total Standby Current
5
TYPICAL PERFORMANCE CHARACTERISTICS
100
100
VDD = 15V
OUTPUT DEAD TIME (%)
RT RESISTANCE (kW)
200pF
470pF
1nF
10
1.8nF
10nF
4.7nF
18nF
10nF
10
1nF
470pF
200pF
4.7nF
VDD = 15V
1
1x104
1x105
1
1x104
5x105
OSCILLATOR FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 2. GM38C42, GM38C43 Output Dead Time
vs. Oscillator Frequency
1.2
8.6
8.4
8.2
8.0
7.8
7.6
7.4
VDD = 15V
VOSC = 2V
7.2
-30
0
30
60
90
120
CURRENT SENSE AMP THRESHOLD (V)
OSC. DISCHARGE CURRENT(mA)
8.8
7.0
-60
1.0
0.8
125°C
25°C
0.6
0.4
-50°C
0.2
0.0
150
0
2
4
6
TEMPERATURE (°C)
ERROR AMPLIFIER OUTPUT (V)
Figure 3. Oscillator Discharge Current vs.
Temperature
Figure 4. Current Sense Amplifier vs.
Error Amplifier Output
120
20
100
80
60
40
20
0
-60
8
25
VDD = 15V
OUTPUT VOLTAGE (V)
VREF SHORT CURCUIT CURRENT (mA)
GM38C42, GM38C43, GM38C44, GM38C45
1x106
Figure 1. Oscillator Frequency Configuration
9.0
6
1x105
15
10
5
0
-5
-10
-30
0
30
60
90
120
150
TEMPERATURE (°C)
Figure 5. Short - Circuit Reference Current vs.
Temperature
-15
0.0
VD = 15V
CL = 1nF
0.2
0.4
0.6
0.8
TIME (µS)
Figure 6. GM38C4X Output Waveform
1.0
Application Information
Familiarity with 384x converter designs is assumed.
GM38C4x has been designed to be compatible with 384xA series controllers.
GM38C4x Advantages
Start-up Current
Start-up current has been reduced to an ultra-low 50µA(typical) permitting higher-valued, lower-wattage, and
start-up resistors (power controller during power supply start-up). The reduced resistor wattage reduces cost and
printed circuit space.
Operating Current
Operating current has been reduced to 4mA compared to 11mA for a typical bipolar controller. The controller runs
cooler and the VDD hold-up capacitance required during start-up may be reduced.
Output Driver
Complementary internal P-and N-channel MOSFETs produce rail-to-rail output voltages for better performance
driving external power MOSFETs. The driver transistor's low on resistance and high peak current capability can
drive gate capacitances of greater than 1000pF. The value of output capacitance which can be driven is
determined only by the rise/fall time requirements. Within the restrictions of output capacity and controller power
dissipation, maximum switching frequency can approach 500kHz.
Design Precautions
When operating near 20V, circuit transients can easily exceed 20V absolute maximum rating and permanently
damaging the controller's CMOS construction. To reduce transients, use a 0.1µF low-ESR capacitor to next to
the controller's supply VDD (or VD for '-1' versions)and ground connections.
Film type capacitors, such as Wima MKS2, are recommended.
Buck Converter
Refer to Figure 7. When at lest 26V is applied to the input, C5 is charged through R2 until the voltage VDD is
greater than 14.5V(the undervoltage lockout value of the GM38C42), output switching begins when Q1is turned
on by the gate drive transformer T1 and charging the output filter capacitor C3 through L1. D5 supplies a
regulated +12V to VDD once the circuit is running.
Current sense transformer CT1 provides current feedback to ISNS for current-mode operation and cycle-by-cycle
current limiting. This is more efficient than a high- power sense resistor and provides the required groundreferenced level shift.
When Q1 turns off, current flow continues from ground through D1 and L1 until Q1 is turned on again.
The 100V Schottky diode D1 reduces the forward voltage drop in the main current path, resulting in higher
efficiency than could be accomplished by using an ultra-fast recovery diode. R1 and C2 suppress parasitic
oscillations from D1.
Using a high-value inductance for L1 and a low-ESR capacitor for C3 permits small capacitance with minimum
output ripple. This inductance value also improves circuit efficiency by reducing the flux swing in L1.
Magnetic components are carefully chosen for minimal loss at 500kHz.
GM38C42, GM38C43, GM38C44, GM38C45
When designing high -frequency converters, avoid capacitive and inductive coupling of the switching waveform
into high impedance circuitry such as the error amplifier, oscillator, and current sense amplifier. Avoid long
printed-circuit traces and component leads. Locate oscillator and compensation circuitry neat the IC. Use high
frequency decoupling capacitors on VERF, and if necessary, on VDD. Return high di/dt currents directly to their
source and use large ground planes.
7
VIN
26V to 40V
Q1
IRF820
CT1
R1
10
1/2W
D4
1N765B
R2
68k
D2
M17Z105
1/4W
0.1µF*
6.8k
D3
MBR030
0.22µF
R4
18
MKS2
100k GM38C42
VREF 8
1 COMP
2
FB
VDD
7
3
ISNS
OUT
6
4
RT/CT
GND
C7
200pF
R5
16k
VOUT
12V, 2A
L1 48µH
31DQ10
C3
D1
3.3µF
C4
0.1µF
C2
1000pF
C5 + 4.7W
4.7µF
0.1µF
D5
T1
1N4001
C8
0.1µF
5
6.19k
1%
1.62k
1%
0.1µF
* Locate near GM38C42 supply pins
GM38C42, GM38C43, GM38C44, GM38C45
Figure 7. 500kHz, 25W, Buck Converter
8
Test
Conditions
Results
Line Regulation
VIN= 26V to 80V, IO= 2A
0.5%
Load Regulation
VIN= 48V, IO= 0.2A to 2A
0.6%
VIN= 48V, IO= 2A
90%
VIN= 48V, IO= 2A (20MHz BW)
100mV
Efficiency
Output Ripple
SOP-8 PACKAGE OUTLINE DIMENSIONS
0.008 +0.0018
-0.0005
0.200
+0.05
-0.01
0 ° ~ 8°
0.028
0.710
+0.013
-0.022
Pad Layout
0.060
+0.33
-0.56
1.52
0.236 ± 0.008
5.990
+0.21
-0.20
0.154
+0.003
-0.004
0.275
0.155
7.0
4.0
PIN INDENT
3.91 ± 0.1
0.024
0.050
0.6
1.270
Inches
( mm )
0.191
+0.002
-0.004
4.850
+0.05
-0.10
0.057 NOM
1.450 NOM
0.063 ± 0.005
1.600 ± 0.130
0.007 ± 0.003
0.175 ± 0.075
0.050 NOM
1.270 NOM
0.016
+0.004
-0.003
0.410
+0.10
-0.08
DIP-8 PACKAGE OUTLINE DIMENSIONS
0.26 ± 0.006
6.60
+0.15
-0.16
0.30
+0.010
-0.015
7.62
+0.25
-0.38
0.36 ± 0.01
9.14
+0.25
-0.26
0.365 ± 0.02
9.27 ± 0.51
0.13
+0.002
-0.006
3.30
+0.05
-0.15
0.180 MAX
4.570 MAX
0.015 MIN
0.380 MIN
0.125 MIN
3.180 MIN
0.018 ± 0.004
0.46 ± 0.10
0.039 ± 0.07
0.99 ± 0.18
0.06 ± 0.01
1.52 +0.26
-0.25
0.100 NOM
2.540 NOM
0.021 ± 0.005
0.53 +0.12
-0.13
(
Inches
)
mm
0.01
+0.002
-0.003
0.25
+0.05
-0.08
GM38C42, GM38C43, GM38C44, GM38C45
( Inches )
mm
9
ORDERING NUMBER
GM 38 C 4X S8 R
Gamma Micro.
Shipping
T: Tube
R: Tape & Reel
Circuit Type
BiCOMS Process
GM38C42, GM38C43, GM38C44, GM38C45
Package
S8: SOP-8
D8: DIP-8
10
11
GM38C42, GM38C43, GM38C44, GM38C45