FAN7391 Datasheet, PDF (11/13 Pages) Fairchild Semiconductor – High-Current, High & Low-Side, Gate-Drive IC

Applications Information
1. Advanced Input Noise Filter
Figure 29 shows the input noise filter method, which has
symmetry duration between the input signal (t_INPUT) and
the output signal (t_OUTPUT) and helps to reject noise
spikes and short pulses. This input filter is applied to the
HIN. The upper pair of waveforms (Example A) shows
an input signal duration (t_INPUT) much longer than input
filter time (t_FLTHIN); it is approximately the same duration
between the input signal time (t_INPUT) and the output
signal time (t_OUTPUT). The lower pair of waveforms
(Example B) shows an input signal time (t_INPUT) slightly
longer than input filter time (t_FLTHIN); it is approximately
the same duration between input signal time (t_INPUT) and
the output signal time (t_OUTPUT).
HIN
t _FLTHIN
t _INPUT
tOUTPUT
HO
HIN
HO
t _FLTHIN
t_INPUT
tOUTPUT
Output duration is
same as input duration
Figure 29. Input Noise Filter Definition
2. Short-Pulsed Input Noise Rejection
Method
The Advanced input filter circuitry provides protection
against short-pulsed input signals caused by noise.
If the input signal duration is less than input filter time
(t_FLTHIN), the output does not change states.
Example A and B of the Figure 30 show the input and
output waveforms with short-pulsed noise spikes with a
duration less than input filter time; the output does not
change states.
HIN
HO
(LOW)
tFLTHIN
t FLTHIN
t FLTHIN
HIN
t_FLTHIN
t _FLTHIN
t _FLTHIN
HO
(HIGH)
Figure 30. Noise Rejecting Input Filter Definition
Figure 31 shows the characteristics of the input filters
while receiving narrow ON and OFF pulses. If input
signal pulse duration, PW_HIN, is less than input filter
time, t_FLTHIN; the output pulse, PW_HO, is zero. The input
signal is rejected by input filter. Once the input signal
pulse duration, PW_HIN, exceeds input filter time, t_FLTHIN,
the output pulse durations, PW_HO, matches the input
pulse durations, PW_HIN. FAN7391 input filter time,
t_FLTHIN, is about 50ns for the high-side outputs.
1000
900
Input Pulse
Output Pulse
800
700
600
500
400
300
200
100
0 _{100 200 300 400 500 600 700 800 900 1000}
Input Pulse Width [ns]
Figure 31. Input Filter Characteristic of Narrow ON
© 2014 Fairchild Semiconductor Corporation
FAN7391 Rev. 1.0.0
11
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