Why isn't high side digital output stable?

Thread Starter

naseeam

Joined Jan 4, 2017
38
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?
 

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JWHassler

Joined Sep 25, 2013
281
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?
Is the SPI connected to any other peripherals?
Are you seeing erroneous operation?
 

Papabravo

Joined Feb 24, 2006
14,406
Normally I/O pins that are configurable, power up in a hi-impedance state, as inputs. In this condition, just about anything can make them beat up and down. It generally takes a few instructions over the SPI bus to configure them properly. If you cannot control the state of the outputs during power up you could add external passive pullups or pulldowns. Let me take a closer look at the datasheet to see if anything jumps out at me.

You need to pay attention to the state transition diagram of Figure 13 in the Infineon datasheet. How are you getting from the SLEEP state via the init arc to the Active state by going through either the Limp Home or the Idle state? Notice in particular that the SPI may be READ ONLY under certain conditions.

Never mind what I said above in paragraph#1. The part about external pullups and pulldowns might be relevant although it might interfere with the diagnostic functions. It is evident to me that this device is designed to behave reasonably BEFORE any SPI communication takes place. The datasheet is long and complex. I urge you to study it in more detail than I have time for. I've pointed to what I think is the correct starting point. What I can't seem to find quickly is the default values of the output transistors on power up in any of the four states.

One more thing. In order for the MOS transistors to function properly the charge pump for the gate voltage has to be alive and well. Can you verify that it is?

I certainly would not commit to using this chip in a design until I had some "Ice Time" with it.

What is your plan for the SPI initialization sequence?
 
Last edited:

nsaspook

Joined Aug 27, 2009
7,587
How about some SPI initialization code and a circuit diagram of at least the complete SPI and uC digital interface to the TLE75620-EST.
 

Thread Starter

naseeam

Joined Jan 4, 2017
38
Low-Level software is periodically writing current to Spider Diagnostic Open Load Register for performing Open Load diagnostics in the OFF state. This is the reason for digital output toggling behavior.
 
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