A8508 View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
A8508
Allegro MicroSystems
'A8508' PDF : 28 Pages View PDF
A8508
Wide Input Voltage Range, High Efficiency
8-Channel Fault Tolerant LED Driver
The waveforms in figure 29 show the operation of the disconnect
feature.
LED short detect
All LEDx pins are rated for 55 V, thus allowing LEDx pin-to-
VOUT short protection in case of a connector short. Any LEDx
pin that has a voltage exceeding VLEDSC will be removed from
operation. This is to prevent the IC dissipating too much power
by having a large voltage present on the LEDx pins.
Input UVLO
When VIN rises above the UVLO threshold (VUVLO(th) ), the
A8508 is enabled. It is disabled when VIN falls below VUVLO(th)
– VUVLO(hys) for more than 2 μs. This lag is to avoid shutdown
because of momentary glitches in the power supply.
VDD and VDR
The VDD pin provides the regulated bias supply for the internal
circuits. A capacitor with a value in the range 0.1 to 1 μF should
be used to decouple the internal analog and digital circuitry.
VOUT
C1
IIN
C2
FAULT
Output short
occurrence
C3
VGIINATE(PMOS)
C4
VOUT
VEN
C2
IOUT
C1
C3
VLEDx
C4
VLEDSC is detected
t
Figure 29. Input disconnect switch shutdown during an output short
condition; shows VOUT (ch1, 20 V/div.), IIN (ch2, 10 A/div.), ¯F¯¯A¯U¯¯L¯¯T¯ (ch3,
5 V/div.), and PMOS device VGATE (ch4, 5 V/div.), t = 50 μs/div.
t
Figure 30. Typical shorted LED: when voltage exceeds VLEDSC , the LED
is disabled and remains disabled until either the EN pin is toggled or the
power cycled; shows VOUT (ch1, 20 V/div.), VEN (ch2, 5 V/div.), IOUT (ch3,
0.5 A/div.), and VLEDx (ch4, 10 V/div.), t = 10 μs/div.
Allegro MicroSystems, Inc.
16
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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