M51995AFP#CF0J Renesas Electronics America, M51995AFP#CF0J Datasheet - Page 35

• 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
2. Over current limiting curve
REJ03D0835-0300 Rev.3.00 Jun 06, 2008
Page 33 of 40
(1) In case of feed forward system
Figure 31 Primary and Secondary Current Waveforms Under the Current Limiting Operation
Figure 31 shows the primary and secondary current wave-forms under the current limiting operation.
At the typical application of pulse-by-pulse primary current detecting circuit, the secondary current depends on
the primary current. As the peak value of secondary current is limited to specified value, the characteristics
curve of output voltage versus output current become to the one as shown in figure 32.
The demerit of the pulse by pulse current limiting system is that the output pulse width can not reduce to less
than some value because of the delay time of low pass filter connected to the CLM terminal and propagation
delay time T
As the frequency becomes higher, the delay time must be shorter. And as the secondary output voltage becomes
higher, the dynamic range of on-duty must be wider; it means that it is required to make the on-duration much
more narrower.
So this system has the demerit at the higher oscillating frequency and higher output voltage applications.
To improve these points, the oscillating frequency is set low using the characteristics of VF terminal.
When the current limiting circuit operates under the over current condition, the oscillating frequency decreases
in accordance with the decrease of VF terminal voltage, if the VF is lower than 3.5V.And also the dead time
becomes longer.
Under the condition of current limiting operation, the output current I2 continues as shown in figure 31. So the
output voltage depends on the product of the input primary voltage V
If the third winding polarity is positive, the V
V
So the sharp current limiting characteristics will be got, if the V
low pass filter as shown in figure 33.
It is recommended to use 15 kΩ for R
OUT
terminal depends on the output DC voltage of the SMPS.
CLM
PDCLM
Figure 32 Over Current Limiting Curve on Feed Forward System
I
1
from CLM terminal to output terminal of type M51995A. The typical T
(a) Feed forward system
R
CLM
Condition on Feed Forward System
I
2
VFFB
, and 10,000 pF for C
Output Current
CC
depends on V
I
I
(b) Primary and secondary current
1
2
IN
VFFB
, so it is concluded that the smoothed voltage of
OUT
voltage if feed back to VF terminal through
in figure 33.
IN
and the on-duty.
PDCLM
I
I
P1
P2
is 100 ns.