DRV8311: Questions about DEV_STS1 and PWM

chun zhang

Part Number: DRV8311

I encountered several issues while using DRV8311P and I need your help

Q1. Before using DRV8311P, read the DEV-STS1 register and the default value obtained is 0x81, indicating that a device error state has occurred

Q2. For PWM, use PWM generation mode; The counting method is Up/Down Mode; PWM_OSC_SYNC used for PWM_OSC_SYNC=2h; Choose complementary PWM; Dead zone configuration is 200ns; Finally, enable PWM. PWM_SYNC is a PWM with a duty cycle of 50% and a 20Khz output from the MCU.

Corresponding register configuration:

PWP_CTRL1: PWM_MODE=11b

DRV_CTRL: TDEAD_CTRL=001b

PWM_STATE=0x777

PWMG_CTRL: PWM_OSC_SYNC=010b; PWMCNTR_MODE=0; PWM_EN=1b;

The waveforms obtained in PWM_SYNC, OUTA, OUTB, and OUTC are as follows

I don't quite understand what clock frequency is used for the PWM generated by DRV8311P at this time? Is it 20M? Does PWM_SYNC_PRD still work for PWP_OSC_SYNC=2h? I don't know how big the CNT corresponding to the cycle is? I'm not sure how to configure the duty cycle

Looking forward to your reply

Thank you.

over 1 year ago

0 hongbo Yang over 1 year ago

Intellectual 310 points

PWM_PRD_OUT controls your PWM period, PWMG_x_DUTY controls duty cycle of each phase A,B,C.

DRV8311P generate approximately 20Mhz internal clock for PWM generation.

As of datasheet of DRV8311P, NO, the PWM_SYNC_PRD is only mentioned in PWM_OSC_SYNC=1h, not 2h.

1 CNT should be think as 1/20Mhz second unit, but the clock is not accurate, so it need to be synced to MCU PWM

0 chun zhang over 1 year ago in reply to hongbo Yang

Prodigy 40 points

When PWP_OSC_SYNC=2h, the period of PWM generated by DRV8311P is the period of PWP_SYNC as shown in the following figure

0 hongbo Yang over 1 year ago in reply to chun zhang

Intellectual 310 points

In this case. You need to control your DRV8311 PWM period by PWM_SYNC. I understand your question, if in that situation, Only when you get the PWM_SYNC_PRD, you can then calculate the accurate PWMG_x_DUTY from it ?

0 chun zhang over 1 year ago in reply to hongbo Yang

Prodigy 40 points

Yes, I found that the frequency I used after calculating PWM_SYNC_PRD was 20M, but I am not sure if it is correct or not, and how large the clock error is. Do we need calibration? I would like to confirm with the official

What mode are you using for PWM_SYNC?

0 hongbo Yang over 1 year ago in reply to chun zhang

Intellectual 310 points

There are multiple locations mentioned the Freq inside DRV8311P is 20Mhz.

Because the 20Mhz is not accurate, that is the reason to use PWM_SYNC.

Currently I am testing in 06h mode.

0 Joshua Maize over 1 year ago in reply to chun zhang

TI__Genius 12231 points

Hi Chun,

Yes the clock frequency is ~20MHz, with no exact level of tolerance available, but as mentioned this is to be mitigated by syncing the device using PWM_SYNC.

Best Regards,

-Joshua

0 chun zhang over 1 year ago in reply to Joshua Maize

Prodigy 40 points

Hi,

Thank you for your reply

I am still confused about Q1 now. Reading register DEV-STS1 yields a value of 0x81

0 Joshua Maize over 1 year ago in reply to chun zhang

TI__Genius 12231 points

Hi Chun,

Yes let me continue to look into that and follow-up later this week.

Best Regards,

-Joshua

0 Joshua Maize over 1 year ago in reply to chun zhang

TI__Genius 12231 points

Hi Chun,

I apologize for the long delay.

If this is still an open question I would like to ask if this 0x81 fault status permanently goes away after being manually cleared? It may have been possible that the fault status was triggered during device power up and an undervoltage condition was briefly met before being cleared, resulting in the need for a manual reset of the status/fault register.

Best Regards,

-Joshua

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DRV8311: Questions about DEV_STS1 and PWM