FAN7387 Fairchild Semiconductor, FAN7387 Datasheet - Page 12

• Manufacturer Part Number: FAN7387
• Description: Fan7387 ? Self-oscillated, High-voltage Gate Driver
• Manufacturer: Fairchild Semiconductor

© 2008 Fairchild Semiconductor Corporation
FAN7387 • 1.0.2
1. Under-Voltage Lockout (UVLO) Function
FAN7387 has a UVLO circuit for a low-side and high-
side block. When V
UVLO circuit is released and the FAN7387 operates
normally. At UVLO condition, the FAN7387 has a low
supply current of less than 130µA. Once UVLO is
released, FAN7387 operates normally until V
below VDD
FAN7387 also has a high-side gate driver. The supply
for the high-side driver is applied between V
To prevent malfunction at low supply voltage between
V
circuit. If V
state to turn off the high-side switch. Once the voltage
of V
VBS
2. Oscillator
The running frequency is determined by an external
timing resistor (R
charge time of capacitor C
determines the running frequency of LO and HO gate
driver output. Figure 30 shows connection configuration.
Figure 31 shows the typical waveforms of RCT, LO, and
HO. From the circuit analysis, the discharging time of
RCT, t, is given by equation 1:
From equation 1, it is possible to calculate discharging
time, t, from V
1/4
Figure 31. Typical Waveforms of RCT,LO and HO
V
RCT
B
VDD.
and V
B
UV
=
-V
V
-, the operation of driver resumes.
DD
S
Figure 30. Typical Connection Method
×
is higher than VBS
In
S
B
UV
(
, FAN7387 provides an additional UVLO
-V
R
-, the UVLO hysteresis.
t
−
S
×
t
DD
C
is under VBS
t
)
to 1/4 V
T
) and timing capacitor (C
DD
reaches to the VDD
DD
UV
by substituting V
UVH,
T
+, the driver holds LOW
from 1/4 V
after V
B
-V
DD
S
B
RCT(t)
UV
DD
exceeds
and V
T
to V
). The
+, the
goes
with
(1)
DD
S
.
12
The running frequency of IC is determined by 1/T and is
approximately given as:
Where, t is the discharging time of the RCT voltage and
T
3. Programming Dead-Time Control / Shutdown
A multi-function pin controls dead-time using an
external resistor (R
using an external switch. This pin should be connected
to an external capacitor to maintain stable operation.
If the voltage of DT/SD is decreased under 1V by an
external switch, such as the TR or MOSFET, the
FAN7387 enters shutdown mode. In this mode, the
FAN7387 doesn’t have any output signal.
4. Gate Driver Operation
The FAN7387 has a two operating modes. One is the
self-oscillation mode by using external timing resistor
(R
the forced oscillation mode by external PWM signal
comes from U-com and the other devices.
Figure 33 shows how to operate IC by using external
PWM circuit with additional resistors (R1 and R2)
because of internal limitation of IC. The input signal
range from an external circuit must be within 3/5 V
and 3/4 V
LO output and HO signal is to in-phase with the external
input signal.
t
f
running
fix
External
Figure 33. Gate Driver Using External PWM Signal
= 38
Signal
T
) and external timing capacitor (C
. 1
is constant value about 450ns of IC.
+14V
=
×
Figure 32. External Shutdown Circuit
T
1
R
DD
=
t
. The external signal produces the HO and
×
( 2
C
t
RDT
Cbp
+
t
1
T
fix
RCT
VDD
DT/SD
GND
DT
)
) and protects abnormal condition
1
2
3
4
T
) and the other is
www.fairchildsemi.com
8
7
6
5
Rev. 1.0
HO
VB
VS
LO
(2)
(3)
DD