Part Number: DRV8308
Hello TI team,
I am facing one issue with our Motor-Driver boards that integrates DRV8303 chip. This board is integrated within an Energy Storage System. This design is in production for more than one year now.
Issue: After the DRV chip has been power cycle. It happens quite frequently that DRV8303 driver isn't responsive anymore on SPI bus after boot-up.
To provide some context, our board integrates a MCU and interfaced through SPI bus to the DRV chip. MCU and DRV chip are powered by two different power supplies: PSU_CTRL for MCU and PSU_PWR for DRV chip and for motor DC bus:
Consecutively to the fact that I was able to repeatably re-create the issue, I instrumented the board to capture PSU_CTRL, PSU_PWR (DRV8308_VM) and DRV8308_VINT (Internal DRV chip core power supply) in order to figure out if this timing behaviour could be the consequence of some internal power supply behavior upon power cycling.
I obtained the following scope capture:
CH1 (Yellow): [Motor 2] PSU_PWR Voltage (DRV_VM)
CH2 (Green): [Motor 2] PSU_CTRL Voltage (3.3 V for MCU)
CH3 (Purple): [Motor 2] DRV8308_VINT Voltage
Step #1: PSU_PWR turned OFF
Step #2: First voltage discontinuity appears on DRV8308_VINT
Step #3: Second voltage discontinuity appears on DRV8308_VINT
In the field, we don't have the possibility to adjust the power cycle OFF time duration. Therefore, we are unable to operate some systems in the field when this issue occurs.
Do you have any idea of what the rootcause can be and what can be a potential way to mitigate that? I would really appreciate any help with this problem.
Many thanks in advance.
I am asking my team about this and I will get back to you soon.
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In reply to Adam Sidelsky:
Thank you for your feedback, below some additional test results I would like to bring to your attention.
Our board is in fact equipped with to identical Motor-Driver function build around the DRV8308 chip. The board I used to perform my test has one particular motor-driver function that is failing at boot-up: Motor Function #2; and the other one that never presents this failure: Motor Function #1. Following previously published test results, I instrumented the other Motor-Driver function DRV8308_VINT Voltage on the same board that never happens to show the issue in order to look for a potential behavior difference. (See scope capture below)
CH1 (Yellow): [Motor #2] PSU_PWR Voltage (DRV_VM)
CH2 (Green): [Motor #2] PSU_CTRL Voltage (3.3 V for MCU)
CH3 (Purple): [Motor #2] DRV8308_VINT Voltage
CH4 (Pink): [Motor #1] DRV8308_VINT Voltage
In reply to user6110249:
This would point to a layout or schematic difference between the two identical drivers on the board. Please compare the two and let me know what you find.
Maybe one of the devices is shutting down quicker because it is farther from the bulk caps or has a smaller bulk cap?
I confirm that bulk capacitor layout + value are identical for both Motor_Funtion #1 and Motor_Funtion #2 of the same board. (VM, VINT and VCP pin)
Moreover it happens on some other failing board that it is actually Motor_Function #1 that is affected instead Motor_Function #2 for the particular one I've tested. Also, some other boards doesn't present this issue at all. It thus doesn't seems to be function/layout dependent.
Do you possibly have any feedback about this DRV8308 chip boot-up issue? Is there any DRV8308 boot-up known problematic behavior and possibly integration strategies to mitigate it?
I am still looking into this and will get back to you tomorrow.
Understood, thank you for your support in attempting to understand the root cause of this issue.
In the case where the boot-up fails, do you see the VINT voltage at 1.8V as expected?
Yes, I confirm VINT Voltage goes back to 1.8V after the chip has been cycled and had failed to boot-up. (See scope capture below) In our my case, the Enable signal is always active during DRV chip power cycle. (I noticed that when Enable signal is low level, VINT Voltage is around 1.35 V)
CH1 (Yellow): [Motor 2] VM VoltageCH2 (Green): [Motor 2] [Motor 2] Enable signalCH3 (Purple): [Motor 2] V_INTCH4 (Pink): [Motor 1] V_INT
Could you try one experiment for us?
Wait until VINT has dropped to at least 300mV before reapplying power and check if the SPI works.
You can place a parallel resistor on VINT to discharge VINT quicker if needed.
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