FAN7389 Datasheet, PDF (15/18 Pages) Fairchild Semiconductor – 3-Phase Half-Bridge Gate-Drive IC

2.4 Fault-Out ( _FO ) and Over-Current Protection
FAN7389 provides an integrated fault output ( _FO) and
an adjustable fault-clear timer (tFLTCLR). There are two
situations that cause the gate driver to report a fault via
the FO pin. The first is an under-voltage condition of
low-side gate driver supply voltage (VDD) and the
second is when the current-sense pin (CS) recognizes a
fault. Once the fault condition occurs, the FO pin is
internally pulled to COM, the fault-clear timer is
activated, and all outputs (HO1,2,3 and LO1,2,3) of the
gate driver are turned off. The fault output stays LOW
until the fault condition has been removed and the fault-
clear timer expires. Once the fault-clear timer expires,
the voltage on the _FO pin returns to pull-up voltage.
The fault-clear time (tFLTCLR) is determined by an
internal current source (IRCIN=5μA) and an external
CRCIN at the RCIN pin, as shown in this equation:
t _FLTCLR
=
C_RCIN × V_RCIN,TH
I _RCIN
[s]
(1)
The RON,RCIN of the MOSFET is a characteristic
discharge curve with respect to the external capacitor
CRCIN. The time constant is defined by the external
capacitor CRCIN and the RON,RCIN of the MOSFET.
The output of current-sense comparator (CS_COMP)
passes a noise filter, which inhibits an over-current
shutdown caused by parasitic voltage spikes of VCS.
This corresponds to a voltage level at the comparator of
VCSTH+ - VCSHYS= 500mV - 60mV =440mV,
where VCSHYS=60mV is the hysteresis of the current
comparator (CS_COMP) as shown in Figure 41.
VDD
RFO
FO
RCIN
CRCIN
Fault
VREF
iRCIN
VRCIN,TH = 3.3V
VRCIN,HYS= 0.7V
3.3V
Q
SET
DOMINANT
S
R
LATCH
To low side output
SOFT-OFF
ISOFT
VDD_UVLO CS_COMP
CS
LEB
0.5V
Protection Circuit
Figure 41.Over-Current Protection
To COM
Figure 42.RCIN and Fault-Clear Waveform Definition
3. Noise Filter
3.1 Input Noise Filter
Figure 43 shows the input noise filter method, which
has symmetry duration between the input signal (tINPUT)
and the output signal (tOUTPUT) and helps to reject noise
spikes and short pulses. This input filter is applied to the
HINx, LINx, and EN inputs. The upper pair of
waveforms (Example A) shows an input signal duration
(tINPUT) much longer than input filter time (tFLTIN); it is
approximately the same duration between the input
signal time (tINPUT) and the output signal time (tOUTPUT).
The lower pair of waveforms (Example B) shows an
input signal time (tINPUT) slightly longer than input filter
time (tFLTIN); it is approximately the same duration
between input signal time (tINPUT) and the output signal
time (tOUTPUT).
Figure 42 shows the waveform definitions of RCIN, FFOO
and the low-side driver, which uses a soft turn-off
method when an under-voltage condition of the low-side
gate driver supply voltage (VDD) or the current-sense pin
(CS) recognizes a fault. Once a fault condition occurs,
the _FO pin is internally pulled to COM and all outputs
(HO1,2,3 and LO1,2,3) of the gate driver are turned off.
Low-side outputs decline linearly by the internal sink
current source (ISOFT=40mA) for soft turn-off, as shown
in Figure 42.
Figure 43.Input Noise Filter Definition
© 2010 Fairchild Semiconductor Corporation
FAN7389 • Rev. 1.0.0
15
www.fairchildsemi.com