DABIC
-
5 8-Channel Source Driver
with Overcurrent Protection
UDN2987x-6
7
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Applications Information and Circuit Description
As with all power integrated circuits, the UDN2987LW-6
has a maximum allowable output current rating. The
500 mA rating does not imply that operation at that value
is permitted or even obtainable. The channel output current
trip point is specified as –370 mA, minimum; therefore,
attempted operation at current levels greater than –370 mA
may cause a fault indication and channel shutdown. The
device is tested at a maximum of –350 mA and that is the
recommended maximum output current per driver. It pro-
vides protection for current overloads or shorted loads up to
30 V.
All outputs are enabled by pulling the OE/R
¯
input high.
When OE/R
¯
is low or allowed to float (internal pull-down),
all outputs are inhibited and the latches are reset. Note that
the reset pulse duration (OE/R
¯
low) should be at least 1 μs.
This will ensure safe operation under attempted reset condi-
tions with a shorted load. The latches are also reset during
power-up, regardless of the state of the OE/R
¯
input.
The load current causes a small voltage drop across the
internal low-value sense resistor. This voltage is com-
pared to the voltage drop across a reference resistor with
a constant current. The two resistors are matched to
eliminate errors due to manufacturing tolerances or tem-
perature effects. Each channel includes a comparator and
its own latch. An overcurrent fault (V
SENSE
> V
REF
) will
set the affected latch and shut down only that channel.
All other channels will continue to operate normally. The
latch includes a 1 μs blanking delay, t
BLANK
, to prevent
unwanted triggering due to crossover currents generated
when switching inductive loads. For an abrupt short circuit,
the blanking and output switching times will allow a brief,
permissible current in excess of the trip current before the
output driver is turned off.
A common thermal shutdown disables all outputs if the
chip temperature exceeds 165°C. At thermal shutdown, all
latches are reset. The outputs are disabled until the chip
cools down to approximately 150°C (thermal hysteresis).
In the event of an overcurrent condition on any channel, or
chip thermal shutdown, the FAULT open-collector output is
pulled low (turned on).
Overcurrent Fault Sense Circuit
+
–
+
–
+
–
V
S
V
REF
V
SENSE
I
LOAD
I
REF
SENSE
To Fault Latch
Matched
REF
