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Description
GM38C4x is fixed frequency, high performance, and current- 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 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. 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
VDD VREF
8 7 6 5
OUT GND
DIP - 8
VDD VREF
8 7 6 5
GM38CXX AYWW OUT GND
GM38CXX
AYWW
1 2 3 4
COMP FB RT / C T ISNS COMP FB
1 2 3 4
RT / C T ISNS
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
IDD VDD VD VISNS VFB IOUT TA
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 TJ
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 ISNS RT / C T GND OUT VDD VREF
BLOCK DIAGRAM
VDD
7
35V 5V Reference UVLO
*
VREF
8
RT / C T
4
Oscillator T Q
OUTPUT
6
FB
2
-
2R R
2.5V
+ -
+
+
S R Q
*
COMP
1
GND*
5
ISNS
3
* 8 - lead versions only
GM38C42, GM38C43, GM38C44, GM38C45
3
PIN LEAD
FUNCTION
FUNCTION
Power Management
ELECTRICAL CHARACTERISTICS
(TA = -40°C to 85°C, Note 4, VDD = 15V, CT=3.3 nF, RT=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
TA = 25°C, IO = 1mA 12V VDD 1 16V, IO = 5µA, (Note 6) IO 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, TA = 25°C, (Note 1) 4.82
5.18 50 5 25 -180
V µV mV mA
TA = 125°C, 1000hrs., (Note 1) -30
-80
Oscillator Section
Initial Accuracy Voltage Stability Temp. Stability Clock Ramp Reset Current Amplitude
TA = 25°C, (Note 5) 12 TMIN VDD TA 16V, (Note 6) TMAX, (Note 1)
49
52 0.2 0.04
55 1.0
KHz % % / °C
TA = 25°C, VRT/CT = 2V, TMIN TA TMAX VRT/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
VFB = 5V VCOMP = 2.5V 2V 12V VO VDD 4V 16V 2.42 65 60 2 -0.5 5.0
-0.1 2.5 90
-2 2.58
µA V dB dB
VFB = 2.7V, VCOMP = 1.1V VFB = 2.3V, VCOMP = 5V VFB = 2.3V, RL = 15k to GND VFB = 2.7V, RL = 15k to VREF (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 VCOMP = 5V, (Note 2) 12V VDD 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
(TA = -40°C to 85°C, Note 4, VDD = 15V, CT=3.3 nF, RT=11kW, unless otherwise noted ) CHARACTERISTICS
Output Section RDS(ON) High RDS(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 ISOURCE = 200mA ISINK = 200mA TA = 25°C, CL = 1nF TA = 25°C, CL = 1nF 20 W 11 40 30 80 60 ns ns
TEST CONDITIONS
MIN
TYP
MAX
UNIT
VDD = 7.5V for GM38C43, GM38C45 Operating Supply Current Zener Voltage (VDD) VFB = VISNS = 0V IDD = 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 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
5
Start - Up Current
VDD = 13V for GM38C42, GM38C44
50
200
TYPICAL PERFORMANCE CHARACTERISTICS
100
200pF
100
OUTPUT DEAD TIME (%)
VDD = 15V
RT RESISTANCE (kW)
470pF
4.7nF
18nF
10
1.8nF 10nF 4.7nF VDD = 15V
1nF
10
10nF
1nF 470pF 200pF
1 1x104
1x105
OSCILLATOR FREQUENCY (Hz)
5x105
1 1x104
1x105
FREQUENCY (Hz)
1x106
Figure 1. Oscillator Frequency Configuration
Figure 2. GM38C42, GM38C43 Output Dead Time vs. Oscillator Frequency
1.2
CURRENT SENSE AMP THRESHOLD (V)
9.0
OSC. DISCHARGE CURRENT(mA)
8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4 7.2 7.0 -60 -30 0 30 60 90
VDD = 15V VOSC = 2V
1.0 0.8 0.6 0.4
-50°C
125°C 25°C
GM38C42, GM38C43, GM38C44, GM38C45
0.2 0.0
120
150
0
2
4
6
8
TEMPERATURE (°C)
ERROR AMPLIFIER OUTPUT (V)
Figure 3. Oscillator Discharge Current vs. Temperature
120
VREF SHORT CURCUIT CURRENT (mA) VDD = 15V
Figure 4. Current Sense Amplifier vs. Error Amplifier Output
25 20
OUTPUT VOLTAGE (V)
100 80 60 40 20 0 -60
15 10 5 0 -5 -10 -15 0.0
VD = 15V CL = 1nF
-30
0
30
60
90
120
150
0.2
0.4
0.6
0.8
1.0
TEMPERATURE (°C)
TIME (µS)
Figure 5. Short - Circuit Reference Current vs. Temperature
Figure 6. GM38C4X Output Waveform
6
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. 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
