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PRODUCT SPECIFICATION
RC5050
11
MOSFET Gate Bias
Figure 4 illustrates how an external 12V supply is used to
bias the output driver supply, VCCQP. A 47
W
resistor is
used to limit the transient current into the VCCQP pin and a
1
m
F capacitor filter is used to filter the VCCQP supply. This
method provides a sufficient gate-to-source bias voltage
(V
GS
) to the MOSFET, and therefore reduces the R
DS,ON
and the resulting power loss within the MOSFET. Figure 5
illustrates how the R
DS,ON
decreases dramatically as V
GS
increases. A 6.2V Zener (D1) is used to clamp the voltage at
VCCQP to a maximum of 12V, thus ensuring that the abso-
lute maximum voltage limit of the IC will not be exceeded.
Figure 4. MOSFET Gate Bias Configuration
PWM/PFM
Control
65-5050-07
+5V
L1
VCCQP
HIDRV
M1
1
μ
F
RS
DS1
D1
6.2V
47
CB
VO
+12V
Note:
1. R
DS,ON
values at Tj = 125
°
C for most devices were extrapolated from the typical operating curves supplied by the
manufacturers and are approximations only.
Table 4. MOSFET Selection Table
Manufacturer & Model #
Fuji
2SK1388
Conditions
1
R
DS, ON
(m
W
)
Typ.
25
37
16.5
28
13
Package
TO-220
Thermal
Resistance
F
JA
=75
Max.
37
—
20
34
15
V
GS
=4V, I
D
=17.5A
T
J
=25
°
C
T
J
=125
°
C
T
J
=25
°
C
T
J
=125
°
C
T
J
=25
°
C
Siliconix
SI4410DY
V
GS
=4.5V, I
D
=5A
SO-8
(SMD)
F
JA
=50
National Semiconductor
NDP706AL
NDP706AEL
National Semiconductor
NDP603AL
National Semiconductor
NDP606AL
Motorola
MTB75N03HDL
Int. Rectifier
IRLZ44
Int. Rectifier
IRL3103S
V
GS
=5V, I
D
=40A
TO-220
F
JA
=62.5
F
JC
=1.5
T
J
=125
°
C
T
J
=25
°
C
T
J
=125
°
C
T
J
=25
°
C
T
J
=125
°
C
T
J
=25
°
C
T
J
=125
°
C
T
J
=25
°
C
T
J
=125
°
C
T
J
=25
°
C
T
J
=125
°
C
20
31
42
22
33
6
9.3
—
—
—
24
40
54
25
40
9
14
28
46
19
31
V
GS
=4.5V, I
D
=10A
TO-220
F
JA
=62.5
F
JC
=2.5
F
JA
=62.5
F
JC
=1.5
F
JA
=62.5
F
JC
=1.0
F
JA
=62.5
F
JC
=1.0
F
JA
=62.5
F
JC
=1.0
V
GS
=5V, I
D
=24A
TO-220
V
GS
=5V, I
D
=37.5A
TO-263
(D
2
PAK)
TO-220
V
GS
=5V, I
D
=31A
V
GS
=4.5V, I
D
=28A
TO-220