FDMF6705B Fairchild Semiconductor, FDMF6705B Datasheet - Page 15

• Manufacturer Part Number: FDMF6705B
• Manufacturer: Fairchild Semiconductor

© 2011 Fairchild Semiconductor Corporation
FDMF6705B • Rev. 1.0.2
Application Information
Supply Capacitor Selection
For the supply inputs (VDRV and VCIN), a local ceramic
bypass capacitor is required to reduce noise and to
supply peak transient currents during gate drive
switching action. It is recommended to use a minimum
capacitor value of 1µF X7R or X5R. Keep this capacitor
close to the VCIN and VDRV pins 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 typically adequate. A
series bootstrap resistor may be needed for specific
applications to improve switching noise immunity. The
boot resistor (R
near the maximum rated V
controlling the high-side MOSFET turn-on slew rate and
VSHW overshoot. Typical R
are effective in reducing VSWH overshoot.
BOOT
), as shown in Figure 28. A bootstrap capacitance
Open -
Drain
Output
PWM
Input
OFF
DISB#
V
BOOT
5V
ON
PWM
Input
OFF
Open -
Drain
Output
DISB#
V
) may be required when operating
5V
ON
A
I
5V
BOOT
C
A
I
5V
VDRV
IN
values from 0.5 to 3.0Ω
SMOD#
DISB#
THWN
PWM
and is effective at
C
Figure 28. Block Diagram with V
VDRV
SMOD
Figure 29. Power Loss Measurement
DISB#
THWN#
PWM
VDRV
FDMF6705B
CGND
FDM 67 5
R
V CIN
VDRV
FDMF6705B
CGND
FDM
VCIN
VCIN
PGND
PGND
5
C
V CIN
VIN
PHASE
BOOT
VSWH
VIN
PHASE
VSWH
15
BOOT
R
BOOT
VCIN Filter
The VDRV pin provides power to the gate drive of the
high-side and low-side power MOSFETs. In most cases,
VDRV can be connected directly to VCIN, which
supplies power to the logic circuitry of the gate driver.
For additional noise immunity, an RC filter can be
inserted between VDRV and VCIN. Recommended
values of 10Ω (R
and 1µF (C
Power Loss and Efficiency
Measurement and Calculation
Refer to Figure 29 for power-loss testing method. Power
loss calculations are:
P
P
P
P
P
EFF
EFF
R
IN
SW
OUT
LOSS_MODULE
LOSS_BOARD
BOOT
C
=(V
C
=V
VIN
MODULE
BOARD
VIN
=V
V V
C
IN
SW
BOOT
A
I
V V
OUT
A
I
IN
IN
SW
C
x I
CIN
BOOT
=100 x P
x I
=100 x P
SW
IN
VCIN
x I
=P
OUT
) + (V
L
=P
Filter
OUT
OUT
V
V
IN
) from VCIN to CGND, Figure 28.
L
IN
IN
IN
(W)
OUT
- P
VCIN
(W)
- P
5V
OUT
C
OUT
SW
OUT
SW
x I
C
) placed between VDRV and VCIN
/P
/P
OUT
5V
(W)
(W)
IN
IN
) (W)
(%)
(%)
I
OUT
A
I
OUT
A
V
OUT
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