FAN7387V Просмотр технического описания (PDF) - Fairchild Semiconductor
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FAN7387V Datasheet PDF : 12 Pages
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Application Information
1. Under-Voltage Lockout (UVLO) Function
FAN7387V has a UVLO circuit for a low-side and high-
side block. When VDD reaches to the VDDUV+, the UVLO
circuit is released and the FAN7387V operates normally.
At UVLO condition, the FAN7387V has a low supply
current of less than 130µA. Once UVLO is released,
FAN7387V operates normally until VDD goes below
VDDUV-, the UVLO hysteresis. FAN7387V also has a
high-side gate driver. The supply for the high-side driver
is applied between VB and VOUT. To prevent malfunction
at low supply voltage between VB and VOUT, FAN7387V
provides an additional UVLO circuit. If VB-VOUT is under
VHSUV+, the driver holds LOW state to turn off the high-
side switch. Once the voltage of VB-VOUT is higher than
VHSUV+, after VB-VOUT exceeds VHSUV-, the operation of
driver resumes.
2. Oscillator
The running frequency is determined by an external
timing resistor (RT) and timing capacitor (CT). The charge
time of capacitor CT from 1/4 VDD to VDD determines the
running frequency of gate driver output (VOUT).
RCT
t
LO
Tfix
Tfix
HO
DT
DT
T
Figure 30. Typical Waveforms of RCT and Internal
Signal (LO, HO) of IC
t = 1.38 • RT • CT
(2)
The running frequency of IC is determined by 1/t and is
approximately given as:
( ) frunning
=
1
t
=
2
t
1
+ t fix
(3)
Figure 29. Typical Connection Method
Figure 30 shows the typical waveforms of RCT and
internal signals (LO and HO) of IC. From the circuit
analysis, the discharging time of RCT, t, is given by:
VRCT (t)
=
VDD
× In⎜⎜⎝⎛
−t
RT • CT
⎟⎟⎠⎞
(1)
where t is the discharging time of the RCT voltage and tfix
is constant value about 450ns of IC.
3. Programming Dead Time Control /
Shutdown
A multi-function pin controls dead time using an external
resistor (RDT) 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 to under 1V by an
external switch, such as the TR or MOSFET, the
FAN7387V enters shutdown mode. In this mode, the
FAN7387V doesn’t have any output signal.
From Equation 1, it is possible to calculate the
discharging time, t, from VDD to one quarter (1/4) of VDD
by substituting VRCT(t) with 1/4 VDD.
Figure 31. External Shutdown Circuit
© 2008 Fairchild Semiconductor Corporation
FAN7387V • 1.0.0
10
www.fairchildsemi.com
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