M51995AFP#CF0J Renesas Electronics America, M51995AFP#CF0J Datasheet - Page 21

• Manufacturer Part Number: M51995AFP#CF0J
• Description: IC SWIT PWM SMPS OVP UVLO 20SOIC
• Manufacturer: Renesas Electronics America

Specifications of M51995AFP#CF0J

• Output Isolation: Isolated
• Frequency Range: 170 ~ 207kHz
• Voltage - Input: 9.9 ~ 36 V
• Power (watts): 1.5W
• Operating Temperature: -30°C ~ 85°C
• Package / Case: 20-SOIC (0.200", 5.30mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

M51995AP/AFP
REJ03D0835-0300 Rev.3.00 Jun 06, 2008
Page 19 of 40
As shown in figure 5, the internal circuit kills the first output pulse in the output waveform. The output waveform
will appear from the second pulse cycle because the duration of first cycle takes C
with that at the stable operating state.
Usually the applied voltage to VF terminal must be proportional the output voltage of the regulator.
So when the over current occurs and the output voltage of the regulator becomes low, the off-duration becomes wide.
There are two methods to get the control voltage, which depends on the output voltage, on primary side. For the fly
back type regulator application, the induced voltage on the third or bias winding is dependent on output voltage. On
the other hand, for the feed forward type regulator application, it can be used that the output voltage depends on the
product of induced voltage and “on-duty”, as the current of choke coil will continue at over load condition, it means
the “continuous current” condition.
Figure 6 shows one of the examples for VF terminal application for the feed forward type regulator.
Figure 4 OSC Waveform with Operation of Intermittent and OSC Control Circuit Operation
Figure 5 Relation between OSC and Output Waveform Circuit Operation at Start-up
Figure 6 Feedback Loop with Low Pass Filter from Output to VF Terminal
Voltage waveform of
CF terminal
Voltage waveform of
output terminal at
Max ON duty
Voltage waveform of
CF terminal
Voltage waveform of
output terminal at
Max ON duty
V
V
≈ 4.4 V
≈ 2.0 V
V
OSCH
V
OSCL
V
V
OSCH
OSCL
V
OH
V
OL
0
0
OH
OL
R
C
VFFB
VFFB
Operation start
No generate
pulse
V
VF
M51995A
OUT
Start from 0 V
First
pulse
F
charging time longer comparing