DRV8251: Maximum Value of MOSFET on Resistance

Shinichi Inoue

Guru 20131 points

Part Number: DRV8251
Other Parts Discussed in Thread: , DRV8231

Dear Specialists,

My customer is considering DRV8251 and DRV8251A, and has a question.

I would be grateful if you could advise.

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Regarding DRV8251 and DRV8251A,

Could you please let me know maximum value of MOSFET (high side and low side) on resistance.

The datasheet describes only typical value.

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I appreciate your great help in advance.

Best regards,

Shinichi

over 1 year ago

+1 Pablo Armet over 1 year ago

TI__Mastermind 37683 points

Hi Shinichi,

Based on our char data, the abs max Rdson for the 8251A is ~370mΩ and for the DRV8231 ~440mΩ. These max specification were taken with small quantity of samples so device to device variations will change the values. Since these specs are not provided in the datasheet, we cannot guarantee to always be accurate.

Regards,

Pablo Armet

0 Brian Dang over 1 year ago in reply to Pablo Armet

Genius 5040 points

Pablo Armet said:
Based on our char data, the abs max Rdson for the 8251A is ~370mΩ

Hi Pablo,

It makes no sense that the abs Rdson of 370mohm is lower than the typical 450 mohms listed. Where do you get this 370mohms?

Brian

+1 Pablo Armet over 1 year ago in reply to Brian Dang

TI__Mastermind 37683 points

Brian,

The RDSon measurements I provided is per FET not LS+HS FET. For this device, the RDSon for both HS and LS are the same. So adding total max RDSon will be 740mΩ.

Regards,

Pablo Armet

0 Brian Dang over 1 year ago in reply to Pablo Armet

Genius 5040 points

Thanks, and it makes perfectly sense now.

Brian

0 Shinichi Inoue over 1 year ago in reply to Brian Dang

Guru 20131 points

Hi Pablo,

Thank you for your reply.

Could I confirm.

DRV8251A Rdson(H+L) = 370mΩ+370mΩ = 740mΩ

You mentioned DRV8231, not DRV8251.

Could you please let me know Rdson of DRV8251.

I appreciate your great help and cooperation.

Best regards,

Shinichi

+1 Pablo Armet over 1 year ago in reply to Shinichi Inoue

TI__Mastermind 37683 points

Shinichi,

The DRV8231 will be 440mΩ + 440mΩ = 880mΩ.

BR,

Pablo

0 Shinichi Inoue over 1 year ago in reply to Pablo Armet

Guru 20131 points

Hi Pablo,

I'd like to confirm Rdson of DRV8251.

Is the Rdson of DRV8251 the same value as DRV8251A（ 370mΩ+370mΩ）or the other value?

Could you please let me know.

I appreciate your great help.

Best regards,

Shinichi

0 Brian Dang over 1 year ago in reply to Shinichi Inoue

Genius 5040 points

Hi,

I'm curious of why you can't use the typical FET on resistance for the design? Why it's critical to know the max value in this case as thermal management should be with high safety margin anyway?

0 Shinichi Inoue over 1 year ago in reply to Brian Dang

Guru 20131 points

Hi Brian,

This is a customer request, so I don't know the details, but I comment in general.

When the ON resistance of the MOSFET increases, the VM voltage decreases. I think that will increase the heat generation and reduce the torque of the motor.
Therefore, I think it is necessary to consider the worst value.

Hi Pablo,

Could you please provide the maximum Rdson of DRV8251.

Is Rdson of DRV8251 （ 370mΩ+370mΩ）?

The customer would like to know if there is a difference in maximum Rdson between DRV8251 and DRV8251A.

I appreciate your great help and cooperation.

Best regards,

Shinichi

+1 Pablo Armet over 1 year ago in reply to Shinichi Inoue

TI__Mastermind 37683 points

Shinichi,

Shinichi Inoue said:
Is the Rdson of DRV8251 the same value as DRV8251A（ 370mΩ+370mΩ）or the other value?

The RDSon of both A and non-A variants is the same.

Regards,

Pablo Armet

0 Shinichi Inoue over 1 year ago in reply to Pablo Armet

Guru 20131 points

Hi Pablo,

Thank you for your reply.

This is the information I'd like to obtain.

I'll share with the customer.

I appreciate your great help and cooperation.

Best regards,

Shinichi

0 Brian Dang over 1 year ago in reply to Shinichi Inoue

Genius 5040 points

Shinichi Inoue said:
When the ON resistance of the MOSFET increases, the VM voltage decreases.

Hi,

Could you provide a reference about when FET on resistance increase (i.e. FET body temperature increases) then VM voltage decreases? VM is supply by an external source in this case I assume.

Brian

0 Shinichi Inoue over 1 year ago in reply to Brian Dang

Guru 20131 points

Hi Brian,

The DRV8251 and DRV8251A have a built-in H-bridge.
When VM is input, it is output to the motor through the built-in FET.
So the VM voltage should drop by the internal FET RDSON multiplied by the motor current.
When we define the OUT pin voltage as VM’
VM' = VM- (Rdson x Imotor)
Therefore, as Rdson increases, VM' decreases and power consumption increase.

I don’t know any more information as it depends on the customer.

Best regards,

Shinichi

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DRV8251: Maximum Value of MOSFET on Resistance