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ADPD4100 LED Over-Current

Hi Analog Devices team!

Quick question for you, curious if this is something that's come up before. I'm trying to drive a pulsed LED using ADPD4100, but something's not operating properly. I've put the chip on a simple breakout PCB attached to a microcontroller, with short wires going from the ADPD4100 to an external red LED. I tied the LED anode to 3.3V (VLED) and the cathode to LED1A, but upon startup it burned out the LED, indicating that the current was over the LED's limit, despite using the configuration from this post (11mA).

I then tried replacing the LED with a 100k resistor to see if I could detect pulsing on an oscilloscope, but the voltage drop across the resistor (e.g. from VLED to LED1A) remains constant at 3.3V during chip operation, with no pulsing. The same is true if I tie the LED cathode to any of the other LED drivers (1A/B, 2A/B, 3A/B, 4A/B), even though some of those drivers should (based on my understanding of the config) be disabled.

Any thoughts as to what would cause this or how I might debug? The obvious hardware issue would be that all the LEDxx pins somehow got tied to ground, but not sure that would happen or how to verify that this is the case. Is there any possible device configuration that would somehow leave all the LED drivers continually active?

Chip communication is happening via SPI with no noticeable issues.

Any thoughts would be much appreciated!



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