A8510 View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
'A8510' PDF : 33 Pages View PDF
A8510
Wide Input Voltage Range, High Efficiency
Fault Tolerant LED Driver
Boost switch overcurrent protection
The boost switch is protected with cycle-by-cycle current
limiting set at a minimum of 3.0 A. There is also a secondary cur-
rent limit that is sensed on the boost switch. When detected this
current limit immediately shuts down the A8510. The level of this
current limit is set above the cycle-by-cycle current limit to pro-
tect the switch from destructive currents when the boost inductor
is shorted. Various boost switch overcurrent conditions are shown
in figures 25 through 27.
Input overcurrent protection and disconnect switch
The primary function of the input disconnect switch is to protect
the system and the device from catastrophic input currents during
a fault condition. The external circuit implementing the discon-
nect is shown in figure 28. If the input disconnect switch is not
used, the VSENSE pin must be tied to VIN and the VGATE pin
must be left open.
IL
IL
C1
SW node
C2
C1
SW node
VOUT
C2
VOUT
C3
EN/PWM
EN/PWM
C3
C3
t
Figure 25. Normal operation of the switch node (SW); inductor current
(IL) and output voltage (VOUT) for 12 series LEDs in each of 8 strings
configuration; shows IL (ch1, 500 mA/div.), SW node (ch2, 20 V/div.), VOUT
(ch3, 20 V/div.), and EN/PWM (ch4, 5 V/div.), t = 1 μs/div.
C4
t
Figure 26. Cycle-by-cycle current limiting; inductor current (IL), note
reduction in output voltage as compared to normal operation with the
same configuration (figure 25); shows IL (ch1, 1 A/div.), SW node (ch2, 20
V/div.), VOUT (ch3, 10 V/div.), and EN/PWM (ch4, 5 V/div.), t = 2 μs/div.
EN/PWM
C1
FAULT
C2
SW node
C3
IL
C4
t
Figure 27. Secondary boost switch current limit; when this limit is hit, the
A8510 immediately shuts down; shows EN/PWM (ch1, 5 V/div.), ¯F¯¯A¯U¯¯L¯¯T¯
(ch2, 5 V/div.), SW node (ch3, 50 V/div.), and IL (ch4, 2 A/div.), t = 200 ns/div.
Allegro MicroSystems, Inc.
19
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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