Part Number: ADS5409
My customer is having a problem with the temperature readback from the ADS5409.
They're accessing the ADC via its 3-wire SPI port and have no problem accessing other internal registers.
No evidence of a problem with the SPI.
The temperature values coming back, however, are questionable.
They've only seen these: 0, 12, 58, 61, 63, 115, and occasionally 141 (decimal).
(While the part is running rather hot, 141C (=285.8F) seems way off.)
They did some testing, which also included using a Fluke temperature probe.
They were able to take readings on the back side of the PCBA, at the ground via array directly under the ADC.
(There are multiple internal ground planes – exactly as on the EVM – and lots of thermal dissipation.
Starting from 25C (room temp), with the unit off, the temperature at the ground via array quickly ramped up to around 65C in a minute or two, but then stayed in that vicinity.
The readback via the SPI port went up in steps roughly as given above (12, 58, 61, 63, 115) and then stayed solidly at 115.
(That’s a 50C differential between the junction temp and the GND plane.)
Any idea what the problem might be?
