M51995AP How To Synchronize With External Circuit - MITSUBISHI

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M51995AP

Manufacturer Part Number
M51995AP
Description
Switching regulator control
Manufacturer
MITSUBISHI
Datasheet
V
OUT
M51995A
Fig.42 Output buffer circuit diagram
DET
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.
C1
C
F/B
C2
M51995A
DET
C4
Fig.43 How to use the DET circuit for the voltage
detector
Fig.44 shows the gain-frequency characteristics between point
B and point C shown in Fig.43.
The G1,
and
are given by following equations;
2
1
R3
G1=
R1/R2
.............................................(11)
1
=
1
............................................(12)
C2 • R3
C1 + C2
=
2
....................................(13)
C1 • C2 • R3
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.
G
AVDET
(DC VOLTAGE GAIN)
G1
2
Log
1
Fig.44 Gain-frequency characteristics between
point B and C shown in Fig.43
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
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.
DETECTING
VOLTAGE
R1
R3

How to synchronize with external circuit

B
Type M51995A has no function to synchronize with external
circuit,however,there is some application circuit for
R2
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.
R
(
/ 27 )
25
M51995AP/FP
SWITCHING REGULATOR CONTROL
.Not to superpose,R1 is connected
(START)
F/B
M51995A
TO PHOTO
COUPLER
How to get the narrow pulse width
Fig.45
during the start of operation
M51995A
T-ON
CF
T-OFF
CT
R
C
OFF
F
ON
Q1
Q2
MINIMUM PULSE
WIDTH OF
MAXIMUM PULSE WIDTH OF
SYNCHRONOUS
SYNCHRONOUS PULSE
PULSE
Fig.46 How to synchronize with external circuit
100
C
120µA
SYNCHRONOU
S
PULSE
0V
0V

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