A8512 View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
'A8512' PDF : 18 Pages View PDF
A8512
LED Backlight Driver for LCD Monitors and Televisions
During normal operation, the IC draws approximately
10 to 15 mA from the VIN pin, depending on switching fre-
quency and the external MOSFET. At VIN = 12 V, this translates
into 120 to 180 mW of power consumption, most of it dissipated
in internal linear regulators. This power increases proportionally
with input voltage. Therefore it is highly recommended to keep
VIN between 10 and 24 V during normal operation.
If the input battery voltage must be higher than 24 V, a better
solution is to power the VIN pin separately using a 12 V supply.
Doing this reduces the heat dissipation of the IC, and improves
the overall system efficiency.
Fault Mode in Single-Controller Operation
Fault State
Auto-
Restart
Description
Over-
voltage
Protection
Fault occurs when output voltage exceeds
Yes
the OVP setpoint voltage. Used to prevent
the output voltage from damaging the power
components.
Pulse-
by-Pulse
Yes
Current Limit
Fault occurs when the current through the
external MOSFET increases such that the
voltage across the SENSE1 and SENSE2 pins
exceeds 95 mV typical. The MOSFET switch is
turned off on a cycle-per-cycle basis.
Multiple pulse-by-pulse current limits will cause
the COMP pin voltage to rise. After a time
Overcurrent
Protection
Yes
period determined by the COMP pin current
and the COMP capacitor, the COMP voltage will
exceed the overcurrent detect threshold, forcing
a fault. System may hiccup if the total current
requirement is too high.
Over-
temperature
Protection
Yes
Fault occurs when the die temperature exceeds
the over-temperature threshold, 165°C typical.
LED Short
Protection
VIN UVLO
No
Fault occurs when the LED pin voltage exceeds
VSC , 25 V typical.
No
Fault occurs when VIN drops below VUVLO,
6.5 V typical. This fault resets all latched faults.
Parallel Operation The A8512 is designed to operate with up
to six A8512 devices connected in parallel, in order to drive a
greater number of LED strings. In this case, the A8512 which
controls the boost converter is designated the master, while the
other devices are slaves which serve as current sinks for their
own LED strings. Slaves communicate with the master through
the shared COMP signal. PWM dimming and protection mecha-
nisms work consistently across all devices.
Select ROVP1 for the master controller such that its OVP set-
point is approximately 10 V above the LED operating voltage
at cold. Select ROVP2 for each slave controller at approximately
15 to 25 kΩ lower than that for the master. This ensures that, in
the case in which an open-LED fault occurs, the slave controllers
will enable OVP before the master does.
Allegro MicroSystems, Inc.
13
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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