DRV8704: Avoid using Rsense

Ivan Torres

Part Number: DRV8704
Other Parts Discussed in Thread: DRV8350, DRV8353, DRV8350R, DRV8353R

Hi,

I'm designing a H-bridge controller for a brushed DC motor (48V @ 30A) and I decided to use the DRV8704. I don't know if there's any full bridge controller that fits better for this application (or maybe two half-bridges synced, I don't know).

The matter is that I don't need the current limiting of the DRV8704 and I want to simplify the PCB as much as possible. In the datasheet of the DRV8701 says that:

"This shunt amplifier feature can be disabled by tying the SP and SN pins to GND. When the amplifier is disabled, current regulation is also disabled."

But I don't know if I could do the same in the DRV8704. Also, I want to drive only one H-bridge so I don't know if there will be any other problem with my design.

Summing up:

- Is there a better solution for driving a brushed DC motor at 48V / 30A with external N-channel MOSFETs? I also want to have 100% duty cycle available.

- Could I remove Rsense and tie the current sense pins to ground?

- Could I use the DRV8704 with only one H bridge?

Thank you.

over 5 years ago

0 Hector Hernandez Luque over 5 years ago

TI__Expert 8985 points

Hi Ivan,

Answers inline:

- Is there a better solution for driving a brushed DC motor at 48V / 30A with external N-channel MOSFETs? I also want to have 100% duty cycle available.

Due to your voltage requirement, that is the best option.

- Could I remove Rsense and tie the current sense pins to ground?

I will verify internally and come back to you.

- Could I use the DRV8704 with only one H bridge?

Yes, you can tie the xIN pins not utilized to GND so the respective half-bridge OUTx pins are High Z.

0 Ivan Torres over 5 years ago in reply to Hector Hernandez Luque

Prodigy 70 points

Thank you!

I'll go on with the layout then. I look forward to your answer regarding the sense resistors ;)

0 Pablo Armet over 5 years ago in reply to Ivan Torres

TI__Mastermind 37683 points

Hi Ivan,

I would like to add a few more things to Hector's response.

- Is there a better solution for driving a brushed DC motor at 48V / 30A with external N-channel MOSFETs? I also want to have 100% duty cycle available.

The DRV8350 (100V three-Phase Smart Gate Driver) would be a better solution considering your voltage specifications. The 8704 has a recommended VM of 52V max which will be cutting close to your 48V Vm. The DRV8350 has a higher operating voltage which will help increase Vm margin. The DRV8350 is also a more power and cost effective device. It has a split rail architecture which will lower the amount of power dissipation.This device will also allow you to drive only one H-bridge at 100% duty cycle and disable the current regulation.

0 Ivan Torres over 5 years ago in reply to Pablo Armet

Prodigy 70 points

Thank you!

We'll take a look at the DRV8350. It seems harder to program but also more versatile.

0 Adam Sidelsky over 5 years ago in reply to Ivan Torres

TI__Guru 63420 points

Ivan,

I support the DRV835x devices and can answer any questions you have!

Here is a link to the DRV8350 EVM which I would recommend for evaluation: http://www.ti.com/tool/DRV8350S-EVM

The DRV8350 does not have current shunt amplifiers (only the DRV8353 does) so that's one less thing to worry about.

If you would benefit from a single output Buck built into the DRV package, we have the DRV8350R available as well which can be used to generate your board's 12V, 5V, or 3.3V rail from the main VM supply.

Regards,

-Adam

0 Ivan Torres over 5 years ago in reply to Adam Sidelsky

Prodigy 70 points

Thank you so much!

I'll take a look at the EVM and I'll come back if I have any question.

In the other hand, I'd appreciate if you could recommend me a MOSFET for continuous 30A @ 48V to use on the H bridge. I've burned some other MOSFETs with lower currents and I wouldn't like to make the same mistake this time.

0 Adam Sidelsky over 5 years ago in reply to Ivan Torres

TI__Guru 63420 points

Ivan,

These may be over-rated but they are what we use on the DRV8353R EVM and can handle 100A easily: http://www.ti.com/lit/ds/symlink/csd19532q5b.pdf

Regards,

-Adam

0 Ivan Torres over 5 years ago in reply to Adam Sidelsky

Prodigy 70 points

I was worried about the "Continuous drain current" rating that appears in the datasheet:

I'd want to make the PCB as small as possible, but maybe I'll need to make some calculations of the PCB trace width necessary for that current.

0 Adam Sidelsky over 5 years ago in reply to Ivan Torres

TI__Guru 63420 points

Ivan,

Do you plan on running at 100% duty cycle for a long while?

Regards,

-Adam

0 Ivan Torres over 5 years ago in reply to Adam Sidelsky

Prodigy 70 points

I'm using the H bridge for driving a coil used for a magnetic levitation experiment:

While we are testing the control of the coil, the control may set 100% duty for several seconds (let's say 5 seconds)

In nominal operation, we'll only have 100% duty for a few milliseconds.

0 Adam Sidelsky over 5 years ago in reply to Ivan Torres

TI__Guru 63420 points

Ivan,

You would need to monitor the system temperature at the PCB and FETs. The temperature would depend on your PCB and environment.

Regards,

-Adam

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DRV8704: Avoid using Rsense