m51996ap Renesas Electronics Corporation., m51996ap Datasheet - Page 22

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

M51996AP/AFP
Application Note of Type M51996AP/AFP
Design of Start-up Circuit and The Power Supply of IC
1. The start-up circuit when it is not necessary to set the start and stop input voltage
2. The start-up circuit when it is not necessary to set the start and stop input voltage
REJ03D0836-0201 Rev.2.01 Nov 14, 2007
Page 22 of 35
Figure 15 Start-up Circuit Diagram When it is Not Necessary to Set The Start and Stop Input Voltage
Figure 15 shows one of the example circuit diagram of the start-up circuit which is used when it is not necessary to
set the start and stop voltage.
It is recommended that the current more than 300 A flows through R1 in order to overcome the operation start-up
current I
operation, so the response time will be long if the product is too much large.
Just after the start-up, the I
supplied from the third winding or bias winding of transformer, the winding ratio of the third winding must be
designed so that the induced voltage may be higher than the operation-stop voltage V
The V
output voltage (V
It is not necessary that the induced voltage is settled higher than the operation start-up voltage V
high gate drive voltage causes high gate dissipation, on the other hand, too low gate drive voltage does not make the
MOS FET fully on-state or the saturation state.
It is recommend to use the third winding of “forward winding” or “positive polarity” as shown in figure 16, when
the DC source voltages at both the IC operation start and stop must be settled at the specified values.
The input voltage (V
current characteristics of type M51996AP/AFP.
The input voltage (V
The V
Where
It is required that the V
V
V
I
V
V
V
V’
V
CCL
IN (START)
IN (STOP)
CC
CC(START)
CC(STOP)
F
CC
IN(START)
IN(P-P)
is the forward voltage of rectifier diode
CC(START)
is the operation start-up current of IC
terminal ≈
voltage is recommended to be 12 V to 17 V as the normal and optimum gate voltage is 10 to 15 V and the
is the peak to peak ripple voltage of
≈ (V
is the operation stop voltage of IC
and V
is the operation start-up voltage of IC
≈ R1 × I
and C
OH
CC (STOP)
) of type M51996AP/AFP is about (V
N
N
IN(START)
IN(STOP)
IN(STOP)
B
P
VCC
CCL
IN(START)
V'
CC
IN RIP (P-P)
is in the range of 10 to 47 F. The product of R1 by C
+ (
Rectified DC
voltage from
smoothing capacitor
), at which the IC operation stops, is decided by the ratio of third winding of transformer.
− V
are given by following equations.
), at which the IC operation starts, is decided by R1 and R2 utilizing the low start-up
current is supplied from C
R1
R2
F
must be higher than V
) ×
M51996A
+ 1) × V
N
N
P
B
+
V
GND
CC
1
2
CC (START)
V'
IN RIP (P-P)
IN(STOP).
……… (7)
VCC
…… (8)
CC
+
R1
, however, under the steady state condition, IC will be
C
VCC
2 V).
V
F
Main transformer
Third winding of
bias winding
VCC
CC(STOP)
causes the time delay of
.
CC(START)
, and the