A8502 View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
'A8502' PDF : 35 Pages View PDF
A8502
Wide Input Voltage Range, High Efficiency
Fault Tolerant LED Driver
frequency, as shown in the following table:
Switching Frequency
Detection Time
(MHz)
(ms)
C1
2
1.5 to 2
C2
1
3 to 4
0.800
3.75 to 5
0.600
5 to 6.7
C3
The LED pin detection voltage thresholds are as follows:
LED1
LED2
LED detection period
ISET
LED Pin Voltage LED Pin Status
<70 mV
Short-to-ground
150 mV
Not used
325 mV
LED pin in use
Action
Power-up is halted
LED removed from operation
None
All unused pins should be connected with a 1.54 kΩ resistor to
ground, as shown in figure 5. The unused pin, with the pull-down
resistor, will be taken out of regulation at this point and will not
contribute to the boost regulation loop.
C4
PWM/EN
t
4B. Example with LED2 pin not being used; the detect voltage is
about 150 mV; shows LED1 (ch1, 500 mV/div.), LED2 (ch2, 500 mV/div.),
ISET (ch3, 1 V/div.), and PWM/EN (ch4, 5 V/div.) pins, time = 500 μs/div.
Short removed
LED1
Pin shorted
LED1
C1
LED detection period
C1
LED2
C2
LED2
C2
ISET
C3
C4
PWM/EN
ISET
C3
C4
PWM/EN
t
t
4A. An LED detect occurring when both LED pins are selected to be used;
shows LED1 (ch1, 500 mV/div.), LED2 (ch2, 500 mV/div.), ISET (ch3,
1 V/div.), and PWM/EN (ch4, 5 V/div.) pins, time = 500 μs/div.
4C. Example with one LED shorted to ground. The IC will not proceed with
power-up until the shorted LED pin is released, at which point the LED is
checked to see if it is being used; shows LED1 (ch1, 500 mV/div.), LED2 (ch2,
500 mV/div.), ISET (ch3, 1 V/div.), and PWM/EN (ch4, 5 V/div.) pins,
time = 1 ms/div.
Allegro MicroSystems, Inc.
12
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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