M51995 Mitsubishi, M51995 Datasheet - Page 15

• Manufacturer Part Number: M51995
• Description: SWITCHING REGULATOR CONTROL
• Manufacturer: Mitsubishi

F/B
WAVEFORM
OF O.S.C. &
POINT A
Fig.9 shows the PWM comparator and latch section. The on-
duration of output waveform coincides with the rising duration of
CF terminal waveform,when the infinitive resistor is connected
between F/B terminal and GND.
When the F/B terminal has finite impedance and current flows
out from F/B terminal,"A" point potential shown in Fig.9 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.
On the other hand,this latch circuit is reset by high level signal
during the dead-time of oscillation(falling duration of oscillation
waveform).So the "B" point potential or output waveform of latch
circuit is the one shown in Fig.10.
The final output waveform or "C" point potential is got by
combining the "B" point signal and dead-time signal
logically.(please refer to Fig.10)
M51995A
PWM comparator and PWM latch section
POINT C
POINT B
6S
~
7.1V
Fig.10 Waveforms of PWM comparator input point A,
Fig.9 PWM comparator and latch circuit
1S
5.8V
latch circuit points B and C
CF
POINT A
OSC WAVEFORM
PWM
COMP
+
-
POINT A
LATCH
POINT B
FROM
OSC
TO
OUTPUT
(
POINT C
15
/ 27 )
Current limiting section
When the current-limit signal is applied before the crossing
instant of "A" pint potential and CF terminal voltage shown in
Fig.9,this signal makes the output "off" and the off state will
continue until next cycle.Fig.11 shows the timing relation among
them.
The current limiting circuit has two input terminals,one has the
detector-sensitivity of +200mV to the GND terminal and the
other has -200mV.The circuit will be latched if the input signal is
over the limit of either terminal.
If the current limiting circuit is set,no waveform is generated at
output terminal however this state is reset during the
succeeding dead-time.
So this current limiting circuit is able to have the function in
every cycle,and is named "pulse-by-pulse current limit".
OSC WAVEFORM
OF CF TERMINAL
WAVEFORM OF
CLM- TERMINAL
OSC WAVEFORM
OF CF TERMINAL
WAVEFORM OF
CLM+ TERMINAL
CURRENT LIMIT
SIGNAL TO SET
LATCH
WAVEFORM OF
V
CURRENT LIMIT
SIGNAL TO SET
LATCH
WAVEFORM OF
V
OUT
OUT
Fig.11 Operating waveforms of current limiting circuit
TERMINAL
TERMINAL
SWITCHING REGULATOR CONTROL
(b) -current limit
(a) +current limit
M51995AP/FP
V
V
THCLM
THCLM
~
~
-200mV
200mV