FDMF6820B Fairchild Semiconductor, FDMF6820B Datasheet - Page 15

• Manufacturer Part Number: FDMF6820B
• Manufacturer: Fairchild Semiconductor

© 2011 Fairchild Semiconductor Corporation
FDMF6820B • Rev. 1.0.2
Application Information
Supply Capacitor Selection
For the supply inputs (V
capacitor is recommended to reduce noise and to
supply the peak current. Use at least a 1µF X7R or X5R
capacitor. Keep this capacitor close to the VCIN pin and
connect it to the GND plane with vias.
Bootstrap Circuit
The bootstrap circuit uses a charge storage capacitor
(C
of 100nF X7R or X5R capacitor is usually adequate. A
series bootstrap resistor may be needed for specific
applications to improve switching noise immunity. The
boot resistor may be required when operating above
15V
MOSFET turn-on slew rate and V
values from 0.5 to 3.0Ω are typically effective in
reducing VSWH overshoot.
BOOT
IN
), as shown in Figure 30. A bootstrap capacitance
and is effective at controlling the high-side
PWM
Input
OFF
Open -
Drain
Output
DISB#
V
Open -
Drain
Output
5V
PWM
Input
OFF
ON
DISB#
V
5V
ON
CIN
A
I
5V
A
I
), a local ceramic bypass
5V
C
VDRV
SHW
C
Figure 29.
SMOD#
DISB#
THWN#
VDRV
PWM
SMOD#
DISB#
THWN#
Figure 30.
PWM
overshoot. R
VDRV
FDMF6820B
VDRV
CGND
FDM 67 5
FDMF6820B
R
CGND
FDM
VCIN
VCIN
VCIN
Block Diagram With V
PGND
Power Loss Measurement
PGND
5
BOOT
VIN
C
VCIN
PHASE
BOOT
VSWH
VIN
PHASE
BOOT
VSWH
15
VCIN Filter
The VDRV pin provides power to the gate drive of the
high-side and low-side power MOSFET. In most cases,
it can be connected directly to VCIN, the pin that
provides power to the logic section of the driver. For
additional noise immunity, an RC filter can be inserted
between the VDRV and VCIN pins. Recommended
values would be 10Ω and 1µF.
Power Loss and Efficiency
Measurement and Calculation
Refer to Figure 30 for power loss testing method.
Power loss calculations are:
P
P
P
P
P
EFF
EFF
R
R
IN
SW
OUT
LOSS_MODULE
LOSS_BOARD
BOOT
BOOT
=(V
C
=V
MODULE
BOARD
VIN
=V
C
VIN
IN
SW
V V
OUT
V V
A
I
C
IN
C
x I
BOOT
=100 x P
BOOT
x I
A
I
IN
=100 x P
SW
SW
IN
x I
=P
CIN
OUT
) + (V
=P
OUT
V
IN
Filter
L
L
IN
IN
(W)
OUT
OUT
- P
V
(W)
- P
IN
5V
OUT
OUT
SW
SW
x I
C
C
/P
/P
OUT
OUT
5V
(W)
(W)
IN
IN
) (W)
(%)
(%)
I
OUT
A
I
OUT
A
V
OUT
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