M51995AFP#CF0J Renesas Electronics America, M51995AFP#CF0J Datasheet - Page 38

• 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. MOS FET gate drive power dissipation
3. Output buffer circuit
REJ03D0835-0300 Rev.3.00 Jun 06, 2008
Page 36 of 40
Figure 39 shows the relation between the applied gate voltage and the stored gate charge.
In the region 1, the charge is mainly stored at C
of MOS FET and the high drain voltage.
In the region 2, the C
state to on-state.
In the region 3, both the C
is low.
The charging and discharging current caused by this gate charge makes the gate power dissipation. The relation
between gate drive current I
Where
As the gate drive current may reach up to several tenths milliamperes at 500 kHz operation, depending on the size of
MOS FET, the power dissipation caused by the gate current can not be neglected.
In this case, following action will be considered to avoid heat up of type M51995A.
(1) To attach the heat sink to type M51995A
(2) To use the printed circuit board with the good thermal conductivity
(3) To use the buffer circuit shown next section
It is recommended to use the output buffer circuit as shown in figure 40, when type M51995A drives the large
capacitive load or bipolar transistor.
I
D
f
Figure 39 The Relation between Applied Gate-Source Voltage and Stored Gate Charge
osc
= Q
is switching frequency
GSH
• f
20
15
10
OSC
5
0
0
(1)
GD
……………………………………………… (11)
Total Stored Gate Charge (nC)
is multiplied by the “mirror effect” as the characteristics of MOS FET transfers from off-
GD
4
D
V
(2)
and C
and total gate charge Q
DS
Figure 40 Output Buffer Circuit Diagram
= 80 V
200 V
320 V
8
GS
(3)
affect to the characteristics as the MOS FET is on-state and the drain voltage
12
M51995A
I
D
= 4 A
16
GS
as the depletion is spread and C
GSH
20
V
is shown by following equation;
OUT
Gate
C
V
GD
GS
GD
C
GS
is small owing to the off-state
Source
Drain
C
I
D
DS
V
D