MC34025 MC33025
Figure 18. Representative Block Diagram
VCC
Vin
16
Vref
4
Clock
5
RT
CT
Ramp
Error Amp Output
3
2
Noninverting Input
Inverting Input
1
8
Soft–Start
CSS
Q
S
R
Error
Amp
+
9.0
µA
Oscillator
6
7
PWM
Comparator
1.25 V
4.2 V
Reference
Regulator
15
VCC
UVLO
9.2 V
VCC
13
VC
14
Output B
Q
Q
11
Current
Limit
1.0 V
9
Current Limit/
Shutdown
Shutdown
1.4 V
Output A
12
Power Ground
Vref
UVLO
R
Q
S
PWM Latch
T
Steering
Flip Flop
0.5 V
Soft–Start Latch
10
Ground
Figure 19. Current Limit Operating Waveforms
CT
Clock
Soft–Start
Error Amp Output
Ramp
PWM
Comparator
Output A
Output B
MOTOROLA ANALOG IC DEVICE DATA
7