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GM3842A Schematic ( PDF Datasheet ) - Gamma

Teilenummer GM3842A
Beschreibung (GM3842A - GM3845A) HIGH PERFORMANCE CURRENT MODE PWM CONTROLLERS
Hersteller Gamma
Logo Gamma Logo 




Gesamt 19 Seiten
GM3842A Datasheet, Funktion
www.DataSheet4U.com
Description
GM384XA series is high performance with fixed-frequency
current mode PWM controllers. They are specially de-
signed for off-Line and DC-to-DC converter applications.
They require minimal external components to precisely tai-
lor performance in a wide variety of applications.
GM384XA series includes a trimmed oscillator for precise
duty cycle control, a temperature-compensated reference,
high gain error amplifier, a current-sensing comparator,
and a high-current totem pole output for driving a power
MOSFET.
On-chip protection features include undervoltage lockouts
with hysteresis for both input and reference, cycle-by-cycle
current limiting, programmable output deadtime, and a
latch for single pulse metering. All these are in a simple
DIP-8 or SOP-8 package!
GM3842A and GM3844A have UVLO thresholds of 16V
(on)/10V(off); GM3843A and GM3845A have UVLO thresh-
olds of 8.4V (on)/ 7.6V (off). GM3842A and GM3843A oper-
ate within 100% duty cycle; GM3844A and GM3845A oper-
ate within 50% duty cycle.
Features
Low Start-Up and Operating Current
Automatic Feed Forward Compensation
Current Mode Operating Frequency up to
500kHz
Trimmed Oscillator Discharge Current for
Precise Duty Cycle Control
Latching PWM for Cycle-By-Cycle Current
Limiting
Undervoltage Lockout with Hysteresis
High Current Totem Pole Output
The GM384XA Have Start-up Current 0.17mA
SIMPLIFIED BLOCK DIAGRAM
Vref 8
RT/ CT 4
Voltage Feedback Input 2
Output Compensation 1
5.0V
REFERENCE
R
R VREF
Undervoltage
LOCKOUT
VCC
7
VCC
Undervoltage
LOCKOUT
OSCILLATOR
Error
Amplifier
+
-
Latching
PWM
5
GND
7 VC
6 Output
5 Power Ground
3 Current Sense Input
www.gammamicro.com 1






GM3842A Datasheet, Funktion
ELECTRICAL CHARACTERISTICS (Continued)
(TA = 0°C to 70°C, *VCC=15V, CT=3.3nF, RT=10kW, unless otherwise specified )
CHARACTERISTICS
SYMBOL
TEST CONDITIONS
MIN
PWM Section
Maximum Duty Cycle
Minimum Duty Cycle
Total Standby Current
Start-Up Current
Operating Supply Current
Zener Voltage
D(MAX)
D(MIN)
GM3842A, GM3843A
GM3844A, GM3845A
IST
ICC(OPR)
VZ
GM3842A/ 43A/ 44A/ 45A
VPIN3= VPIN2=0V
ICC= 25mA
95
47
30
* Adjust VCC above the Startup threshold before setting to 15 V.
Note1: Parameter measured at trip point of latch with VPIN2 = 0.
Note2: Gain defined as A=DVPIN1 / DVPIN3 ; 0 VPIN3 0.8V
Note3: These parameters, although guaranteed, are not 100% tested in production
TYP MAX UNIT
97
48
0.17
13
38
100
50
0
0.3
17
%
%
%
mA
mA
V
TYPICAL PERFORMANCE CHARACTERISTICS
RT
(KW)
50
CT= 1nF
20
CT= 1000pF
CT= 200pF
CT= 500pF
10
CT= 5nF
5
CT= 10pF
CT= 2nF
2 VCC= 15V
1 TA=25°C
10 20 30
50
100 200 300 500
fosc
(kHz)
Figure 1. Timing Resistor vs. Oscillator Frequency
%
VCC= 15V
TA=25°C
50
30
CT= 5nF
20
CT= 10pF
10 CT= 2nF
CT= 1nF
5
CT= 500pF
CT= 200pF
CT= 1000pF
3
2
1
10 20 30 50
100 200 300 500
fosc
(kHz)
Figure 2. Output Dead-Time vs. Oscillator Frequency
6

6 Page









GM3842A pdf, datenblatt
Figure 12. Adjustable reduction of clamp level
Vclamp=
(
1.67
R2
R1
+
1)
+0.33X10-3
R1
(R1
+
+
R2
R2 )
IPK(max)=
Vclamp
RS
8
where: 0 Vclamp 1.0V
R2
4
2
1
R1
VCC 7
R
Internal
R Bias
Oscillator
5.0 Vref
+
-
+
-
+
-
+
-
+
+ 1.0mA
-
Error
Amplifier
Vclamp
2R
-
+
S
Q
R
Comp/ Latch
R
1.0V
5
VCC VIN
7
6 Q1
5
3
RS
Figure 13. Soft-start circuit
tsoft-start 3600C in µF
8
4
2
1
1.0M
C
R
Internal
Bias
R
Oscillator
5.0 Vref
+
-
+
-
+
+
-
Error
Amplifier
1.0mA
2R
R
+
-
1.0V
5
S
Q
R
12

12 Page





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