M51995 Mitsubishi, M51995 Datasheet - Page 25

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

Fig.43 shows how to use the DET circuit for the voltage detector
and error amplifier.
For the phase shift compensation,it is recommended to
connected the CR network between det terminal and F/B
terminal.
DET
Fig.44 shows the gain-frequency characteristics between point
B and point C shown in Fig.43.
The G1,
G1=
At the start of the operation,there happen to be no output pulse
due to F/B terminal current through C1 and C2,as the potential
of F/B terminal rises sharply just after the start of the operation.
Fig.43 How to use the DET circuit for the voltage
1
2
=
=
C2 • R3
M51995A
R1/R2
C1 • C2 • R3
Fig.44 Gain-frequency characteristics between
R3
C1 + C2
G1
1
detector
1
and
Fig.42 Output buffer circuit diagram
.............................................(11)
point B and C shown in Fig.43
............................................(12)
M51995A
Log
2
are given by following equations;
....................................(13)
DET
F/B
G
(DC VOLTAGE GAIN)
AVDET
C
1
V
C4
C2
OUT
2
C1
R3
R1
R2
B
DETECTING
VOLTAGE
(
25
/ 27 )
How to synchronize with external circuit
Type M51995A has no function to synchronize with external
circuit,however,there is some application circuit for
synchronization as shown in Fig.46.If this circuit is used,the
synchronization may be out of order at the overload condition
when the current limiting function starts to operate and VF
terminal voltage becomes lower than 3V.
Fig.45 shows how to get the narrow pulse width during the start
of the operation.If the pulse train of forcedly narrowed pulse-
width continues too long,the misstart of operation may
happen,so it is recommended to make the output pulse width
narrow only for a few pulse at the start of operation.0.1µF is
recommended for the C.
Not to lack the output pulse,is recommended to connect the
capacitor C4 as shown by broken line.
Please take notice that the current flows through the R1 and R2
are superposed to Icc
to Cvcc2 as shown in Fig.27.
How to get the narrow pulse width during the
start of operation
R
ON
Fig.45
T-ON
Fig.46 How to synchronize with external circuit
M51995A
SWITCHING REGULATOR CONTROL
C
MINIMUM PULSE
WIDTH OF
SYNCHRONOUS
PULSE
How to get the narrow pulse width
during the start of operation
F
CF
M51995A
R
(START)
OFF
T-OFF
.Not to superpose,R1 is connected
Q1
F/B
MAXIMUM PULSE WIDTH OF
SYNCHRONOUS PULSE
M51995AP/FP
TO PHOTO
COUPLER
CT
Q2
100
C
120µA
SYNCHRONOU
S
PULSE
0V
0V