Hello,
I'm using the ADN8835 in digital mode to control the current to a TEC where the input voltage is provided by a DAC. The current limits are set to 2.5A cooling and 1.0A heating and Vlim is tied to Vref so as to limit the TEC voltage by the supply voltage (+5.0 Vdc).
Vtec and Itec are read by independent ADCs which allows me to get diagnostics from the ADN8835.
A snippet of my circuit is shown below:
I've have recently started to see a few different failure modes of the ADN8835 such as:
- No heating or cooling current due to a short of the linear power stage (Vtec measurement = 5V, Itec measurement = 4.4A)
- No heating current, yet cooling functionality seems ok however both Vtec and Itec measurements are giving 0V and 0A respectively
- Low current in cooling mode (0.8A reported from Itec), cooling of TEC is observed, but at a much slower rate than expected
- No heating or cooling currents, Itec measurement = 2.5A, Vtec changing from -0.5 Vdc to -2.4 Vdc
I've confirmed that the TEC devices connected remain undamaged.
One IC has been removed from failure case 1) and impedances have been measured from:
- VinL to LDR = 17 Ohms
- LDR to GND-L = 2 Ohms
In this case the PWM output stage seems OK (High impedances measured). Other ICs have not yet been removed and some have been sent off for Xray imaging of the soldering.
I can see that a similar issue was reported here a couple of years ago (without resolution) and in trying to replicate our issue I've set our DAC output voltage to change from +1.25 Vdc to both +2.5 Vdc and +0.0 Vdc instantaneously over many hours without observing any failures of the ADN8835. I've been using this device on the PCBA for a few years now and only started seeing this issue recently, so I suspect that a manufacturing (SMD) process change or my assembly process may be a contributing factor, but I'd like to know what can cause damage to the output stages.
Placing the TEC load into both momentary short and open-circuit conditions do not cause the ADN8835 to fail. Running in 100% cooling and heating conditions for long periods of time also do not replicate the failure mode.
There is also no mention of ESD protection in the ADN8835 datasheet, so I wonder can ESD damage the only the output stages of this IC? Note that I have many other sensitive devices on the same PCBA (FPGA, DDR4, etc...) and none of these other devices appear damaged, only the ADN8835 output stage.
Looking for ADI's assistance on this one.
Thanks.