DRV8704: BLANK register

NAOKI AOYAMA

Guru 11215 points

Part Number: DRV8704

Hello,

Our customer use the DRV8704, have a question about BLANK Register.

The register have 0x32h offset, so when writing data from 0x00h to 0x32h, tBLANK is 1.05us.

If the customer write a larger data, tBLANK is set in increments of 21ns.

It is mentioned writing 0xFF, tBLANK is 5.880us. But I calculate it, it is 5.355us.

Which is correct?

Best Regards,

Naoki Aoyama

over 5 years ago

0 Rick Duncan over 5 years ago

TI__Guru** 114905 points

Hi Aoyoma-san,

Your math is correct for 21ns increments.

We will have to research this to confirm the 21 ns increment is correct. This may take until next Tuesday due to an upcoming holiday.

0 NAOKI AOYAMA over 5 years ago in reply to Rick Duncan

Guru 11215 points

Hi Rick-san,

Thank you for your reply.
I will wait for your research.

Regards,
Naoki Aoyama

0 Rick Duncan over 5 years ago in reply to NAOKI AOYAMA

TI__Guru** 114905 points

Hi Aoyama-san,

The calculation in the BLANK register section of the datasheet is incorrect as you pointed out.

The corrected values are listed to the right

0x00h: 1.05 µs

…

0x32h: 1.05 µs

0x33h: 1.07 µs

…

0xFEh: 5.859 µs 5.314 µs

0xFFh: 5.880 µs 5.335 µs

Also please note section 7.3.5 has an error. It should read:

After the current is enabled in an H-bridge, the voltage on the ISEN pin is ignored for a period of time before

enabling the current sense circuitry. This blanking time is adjustable from 500 ns 1us to 5.14 5.355µs, in 20- 21 ns increments,

by setting the TBLANK bits in the BLANK register. Note that the blanking time also sets the minimum drive time

of the PWM.

0 NAOKI AOYAMA over 5 years ago in reply to Rick Duncan

Guru 11215 points

Hi Rick-san,

Thank you for your research.
I will calculate TBLANK simply.

Thanks
Naoki Aoyama

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DRV8704: BLANK register