DVR8305 Dead-time is not stable

Xiaowei Bai1

Other Parts Discussed in Thread: DRV8305

hello,

My customer used the DRV8305 to develop the motor control board, now we met the issue is dead-time is not stable of DRV8305, The dead-time configured as 0.5us. but some time, there is no dead-time of DRV8305 output, and the HS and LS occur short in minute time.

Do you know why, and any comments for it? thanks very much!

the waveform as below:

1. correct waveform as picture one(purple and green line are the PWM input of DRV8305; yellow and blue are the PWM output of DRV8305 )

2. incorrect waveform as picture two(purple and green line are the PWM input of DRV8305; yellow and blue are the PWM output of DRV8305 )

over 9 years ago

0 Rick Duncan over 9 years ago

TI__Guru** 114905 points

Hi Xiaowei,

Is it possible to increase the number of samples/second, and double check your findings?

If the number of samples is 5M/s, this works out to 200ns between samples. The zoomed scope capture could be presenting suspect data.

0 Xiaowei Bai1 over 9 years ago in reply to Rick Duncan

TI__Intellectual 1205 points

Hello Rick,
ok, I will check it. and can you let me know what is the accuracy of DRV8305 timer? thanks..

0 Xiaowei Bai1 over 9 years ago in reply to Xiaowei Bai1

TI__Intellectual 1205 points

hello Rick,
we confirmed this phenomenon don't come from samples rate. so can help check it? thanks..

0 Nicholas Oborny over 9 years ago

TI__Mastermind 21320 points

Xiaowei,

What is the direction of the current out of the half-bridge in each of these captures?

If current is a different direction in each of these captures, it can cause the output voltages to look different due to the freewheeling diode of the power MOSFET.

I don't see a shoot-through event in these captures. I just see the SH node flying high after GL turns OFF. The body diode will limit out how high SH can fly and then 0.5us later GH will turn ON.

0 Xiaowei Bai1 over 9 years ago in reply to Nicholas Oborny

TI__Intellectual 1205 points

hello Nick,
thanks for your feedback. For current wave I will update later.

I think you said the picture 1, yes, the picture 1 is the correct. but you can take a look the picture 2, it is incorrect, there is not the dead-time . thanks..

0 Nicholas Oborny over 9 years ago in reply to Xiaowei Bai1

TI__Mastermind 21320 points

Hi Xiaowei,

Dead time is not measured to when SH_X goes high. They need to measure the differential voltage on the HS VGS to understand when the HS MOSFET is being enabled. Else, the dead-time could be masked by the voltage flying up through the body diode.

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DVR8305 Dead-time is not stable