VN750-E / VN750S-E / VN750PT-E / VN750B5-E
OPEN LOAD DETECTION IN OFF STATE
Off state open load detection requires an external pull-up
resistor (R
PU
) connected between OUTPUT pin and a
positive supply voltage (V
PU
) like the +5V line used to
supply the microprocessor.
The external resistor has to be selected according to the
following requirements:
1) no false open load indication when load is connected:
in this case we have to avoid V
OUT
to be higher than
V
Olmin
; this results in the following condition
V
OUT
=(V
PU
/(R
L
+R
PU
))R
L
<V
Olmin.
2) no misdetection when load is disconnected: in this
case the V
OUT
has to be higher than V
OLmax
; this
results in the following condition R
PU
<(V
PU–
V
OLmax
)/
I
L(off2)
.
Because I
s(OFF)
may significantly increase if V
out
is
pulled high (up to several mA), the pull-up resistor R
PU
should be connected to a supply that is switched OFF
when the module is in standby.
The values of V
OLmin
, V
OLmax
and I
L(off2)
are available in
the Electrical Characteristics section.
Figure 9. Open Load detection in off state
V batt.
V
PU
V
CC
R
PU
INPUT
DRIVER
+
LOGIC
OUT
+
R
STATUS
-
V
OL
R
L
I
L(off2)
GROUND
10/31
STMICROELECTRONICS [ STMICROELECTRONICS ]
