Rainbow Electronics ATA6823 - Manual (Page 14)

14
4856E–AUTO–07/07
ATA6823 [Preliminary]
Figure 5-5. Timing of the Drivers
The delays t
HxLH
and t
LxLH
include the cross conduction time t
CC
.
5.12 Short Circuit Detection
To detect a short in H-bridge circuitry, internal comparators detect the voltage difference
between source and drain of the external power NMOS. If the transistors are switched ON and
the source-drain voltage difference is higher than the value V
SC
(4V with tolerances) for a time
> t
SC
(typically 10 µs) the signal SC (short circuit) will be set and the drivers will be switched off
immediately. The diagnostic pin DG1 will be set to “H”. With the next transition on pin PWM, the
bit will be cleared and the corresponding drivers, depending on the DIR pin, will be switched on
again.
There is a PBAT supervision block implemented to detect the possible voltage drop on PBAT
during a short circuit. If the voltage at PBAT falls under V
SCPB
(5.6V with tolerances) for a time
> t
SC
the drivers will be switched off immediately and DG1 will be set to “H”. It will be cleared as
above.
t
LxLH
t
Lxr
t
HxLH
t
Hxr
t
CC
t
HxHL
t
Hxf
t
LxHL
t
Lxf
t
CC
Hx
Lx
PWM or
DIR
80%
50%
20%
80%
20%
t
t
t