UDN2987 Allegro MicroSystems, Inc., UDN2987 Datasheet - Page 7

• Manufacturer Part Number: UDN2987
• Description: Dabic-5 8-channel Source Driver With Overcurrent Protection
• Manufacturer: Allegro MicroSystems, Inc.

UDN2987x-6
As with all power integrated circuits, the UDN2987A-6 and
UDN2987LW-6 have 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 out-
put 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
shut down. The device is tested at a maximum of –350 mA
and that is the recommended maximum output current
per driver. It provides 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-
Applications Information and Circuit Description
To Fault Latch
Overcurrent Fault Sense Circuit
–
+
SENSE
REF
V
DABIC-5 8-Channel Source Driver
REF
+
–
pared to the voltage drop across a reference resistor with
a constant current. The two resistors are matched to elimi-
nate errors due to manufacturing tolerances or tempera-
ture effects. Each channel includes a comparator and its
own latch. An overcurrent fault (V
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
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,
permissable current in excess of the trip current before the
output driver is turned off.
A common thermal shut down disables all outputs if the
chip temperature exceeds 165°C. At thermal shut down,
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 shut down, the FAULT open-collector output
is pulled low (turned on).
I
REF
Matched
with Overcurrent Protection
V
I
LOAD
S
+
V
–
SENSE
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
SENSE
BLANK
> V
, to prevent
REF
) will set
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