LM25085A: Motor drive using SWPS

na na78

Guru 16770 points

Part Number: LM25085A

The customer considers DC motor drive system using LM25085A.

The requirement for LM25085A is as follows.

INPUT:17V-25.2V

OUTPUT : 16.2V/3A (8A peak)

EN function

4276.e2e.xlsx

It does not have motor driver, just applied power to motor directly and rotation is controlled by EN of LM25085A.

To wait output stable before applying voltage to motor, FET is inserted at Vout. FET ON/OFF is controlled by MCU.

In addition, to protect the impact of back EMF from motor, diode is inserted prior the motor.

Do you think it is feasible?

Could you please give me your feedback if you had concern?

BestRegards

over 6 years ago

0 Robert Blattner over 6 years ago

TI__Expert 6245 points

Hello Na Na,

The converter is fine. Make sure that the output cap is within specifications outlined in the datasheet. You do not specify what you want the output for the converter to be so I am assuming that it will be over 5 V. In this case, the power FET in series with the motor should be moved to the bottom of the motor, a freewheeling diode back to the converter’s output would be useful to keep the peak voltage across the FET from spiking, or if you wish to leave the FET where it is, replace it with a PFET and level shifter. See below.

Regards, Robert

0 Robert Blattner over 6 years ago in reply to Robert Blattner

TI__Expert 6245 points

Picture did not post so trying again...

0 Robert Blattner over 6 years ago in reply to Robert Blattner

TI__Expert 6245 points

Hello NaNa,

Since you have not had any new question over the last few days, I am assuming that your question has been answered.

Regards, Robert

0 na na78 over 6 years ago in reply to Robert Blattner

Guru 16770 points

Hi Robert

Sorry for late response.

I'm considering FETs by TI that can be support the requirement.
Regarding to Power FET, I think there is no recommendation. Is my understanding correct?
Do you have general purpose FET you can recommend?

BestRegards

0 Robert Blattner over 6 years ago in reply to na na78

TI__Expert 6245 points

Hello NaNA,

The primary specification of concern is on-resistance and block voltage. This determins if the device can handle the current and voltage that you want. Also, I show a p-channel in the diagram since it is easier to switch. An n-channel may require a charge pump. Also, the circuit becomes a little more complicated if voltage exceeds the rated gate voltage of the FET.

Regards, Robert

0 na na78 over 6 years ago in reply to Robert Blattner

Guru 16770 points

Hi Robert

Thank you for your reply.

I will continue consideration to feasible design.

BestRegards

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LM25085A: Motor drive using SWPS