FAN7387 Datasheet, PDF (13/17 Pages) Fairchild Semiconductor – Self-Oscillated, High-Voltage Gate Driver

Typical Application Informations
1. UVLO (Under-Voltage Lockout) Function
FAN7387 has a UVLO circuit for a low-side and high-
side block. When V_DD reaches to the V_DDUV+, the 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_DD goes below
V_DDUV-, the UVLO hysteresis.
FAN7387 also has a high-side gate driver. The supply for
the high-side driver is applied between V_B and V_S. To
prevent malfunction at low supply voltage between V_B
and V_S, FAN7387 provides an additional UVLO circuit. If
V_B-V_S is under V_BSUV+, the driver holds LOW state to
turn off the high-side switch. Once the voltage of V_B-V_S
is higher than V_BSUVH after V_B-V_S exceeds V_BSUV-, the
operation of driver resumes.
2. Oscillator
The running frequency is determined by an external
timing resistor (R_T) and timing capacitor (C_T). The
charge time of capacitor C_T from 1/4 V_DD to V_DD
determines the running frequency of LO and HO gate
driver output. Figure 30 shows connection configuration.
RCT
t
LO
T_fix
T_fix
HO
DT
DT
T
Figure 31. Typical Waveforms of RCT, LO, and HO
t 1.38 RT CT
(2)
The running frequency of IC is determined by 1/T and is
approximately given as:
VDD
RCT ₁
CT
VDD ₂
DT/SD 3
RT
GND ₄
8 VB
7 ^HO
6 VS
5 ^LO
1
1
f _{r u nn ing}
T
2 t T_fix
(3)
where t is the discharging time of the RCT voltage and
and T_fix is constant value about 450ns of IC.
FAN7387 Rev1.0
Figure 30. Typical Connection Method
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:
V_RCT t
‐t
VDD In
RT CT
(1)
3. Programming Dead Time Control / Shutdown
A multi-function pin controls dead time using an external
resistor (R_DT) and protects abnormal condition 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.
From Equation 1, it is possible to calculate discharging
time, t, from V_DD to 1/4 V_DD by substituting V_RCT(t) with
1/4 V_DD.
© 2008 Fairchild Semiconductor Corporation
FAN7387 Rev. 1.0.0
13
www.fairchildsemi.com