m51996ap Renesas Electronics Corporation., m51996ap Datasheet - Page 17

• Manufacturer Part Number: m51996ap
• Description: Switching Regulator Control
• Manufacturer: Renesas Electronics Corporation.

M51996AP/AFP
PWM Comparator, PWM Latch and Current Limit Latch Section
Figure 7 shows the schematic diagram of PWM comparator and PWM latch section. The on-duration of output
waveform coincides with the rising duration of CF terminal waveform, when the no output current flows from F/B
terminal.
When the F/B terminal has finite impedance and current flows out from F/B terminal, “A” point potential shown in
figure 7 depends on this current. So the “A” point potential is close to GND level when the flow-out current becomes
large.
“A” point potential is compared with the CF terminal oscillator waveform and PWM comparator, and the latch circuit is
set when the potential of oscillator waveform is higher than “A” point potential.
The latch circuit is reset during the dead-time of oscillation (falling duration of oscillation current). So the “B” point
potential or output waveform of latch circuit is the one shown in figure 8.
The final output waveform or “C” point potential is got by combining the “B” point signal and dead-time signal
logically. (please refer to figure 8)
REJ03D0836-0201 Rev.2.01 Nov 14, 2007
Page 17 of 35
F/B
Figure 8 Waveforms of PWM Comparator Input Point A, Latch Circuit Points B and C
M51996A
Notes: 1. Resistor to determine current limit sensitivety
6 S
Figure 7 PWM Comparator PWM Latch and Current Limit Latch Section
≈ 7.1 V
2. High level during dead time
OSC & point A
Waveform of
1 S
Point B
Point C
5.8 V
CF
Point A
PWM
COMP.
−
+
Point D
OSC waveform
CLM+
*1
200 µA
Waveform at point A
current
Latch
Point B
*2
From
OSC
To
output
Point C