DRV8847: Strange behaviour of DRV8847 in parallel bridge mode

Andy Rutter

Part Number: DRV8847

I am using DRV8847 with MODE=1 and IN3=1. At PWM frequencies below 2kHz, the device operates as expected. Above this frequency the outputs that should be L have a signal that is in opposite phase to the H outputs (ref Table 5 in datasheet) - e.g. if IN1=0V and IN2 has the input PWM signal, OUT2 and OUT4 produce the expected PWM but OUT1 and OUT3 produce the antiphase signal up to approx 30% PWM and then the OUT1/3 pulse width decreases as the input pulse width increases. The result is that the connected motor does not start until the input signal has reached approx 30% pulse width.

Has anyone observed this effect and know what is causing it?

-- Andy

over 1 year ago

0 Keerthivasan Kumanan over 1 year ago

TI__Mastermind 18615 points

Hi Andy,

Give me 24 hours to look into this and get back to you.

Best,

Keerthi

0 Keerthivasan Kumanan over 1 year ago in reply to Keerthivasan Kumanan

TI__Mastermind 18615 points

Hi Andy,

Are you using our EVM. If not, can you send me a schematic of you board and can you try the same procedure with our EVM. I am going to try it on my end with an EVM as well. I will give you an update by the end of this week.

Best,

Keerthi

0 Andy Rutter over 1 year ago in reply to Keerthivasan Kumanan

Prodigy 50 points

Hi Keerthi

Thank you for taking the time to investigage this. I have attached an image of the circuit. Vin varies between 5V and 13V and there is a 22uF capacitor on Vin. PWM1/2 are driven direct from an AVR and OUT1/2 are connected direct to the load - either resistive for testing or a iron core motor (e.g. Re280).

-- Andy

22uF