Why isn't high side digital output stable?

[jani12]

Our Advanced Drive Assist Systems(ADAS) project is based on Renesas RH850/U2A16 microcontroller. We are using Infineon Technologies TLE75620-EST, SPI Driver for Enhanced Relay Control IC for driving loads. Datasheet is attached. We don't have any loads connected to SPIDER output pins. We're not commanding digital output logic low or logic high. On power up, SPIDER digital outputs pins are not stable. They are toggling between logic high and logic low. Attached is SPIDER OUT0_HS pin unstable waveform measured with oscilloscope.

When we stop code execution, output pin is stable. Please see attached SPIDER OUT0_HS pin stable waveform.

Microcontroller communicates with SPIDER chip over spi interface. Instead of stopping code execution, if we dynamically disable spi communications, would the digital output become stable?

Why is the digital output toggling? Microcontroller is using spi interface for control and diagnosis. Are we sending something over SPI that's commanding the digital output to toggle?

 

[Diver300]

Are we sending something over SPI that's commanding the digital output to toggle?

Yes. There is no accurate clock, and possibly no clock at all, in the TLE75620, so the only way that it could have a change in state that is repeating precisely 100 ms after the previous one, is for something to tell it to do so.

 

[jani12]

>> so the only way that it could have a change in state that is repeating precisely 100 ms after the previous one, is for something to tell it to do so.
That's correct! Low-level software is writing current to diagnostic Open Load register every 100ms for performing open load diagnostics in the off state. Writing to this register at regular intervals results in output togging behavior.

 

[KeepItSimpleStupid]

Did you by chance enable the internal PWM generator?