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DRV8703-Q1: Influence of GND Level Difference

hideyuki sakai
Mastermind 6250 points
Part Number: DRV8703-Q1

Dear Sir.

My customer is evalating DRV8703-Q1 as brushed motor pre-driver for their system.

At this time, OEM pointing out the GND level difference between DRV8703-Q1 GND

and Motor GND. It may be around 1 ~ 1.5V.

DRV8703-Q1 GND is a kind of ECU GND. Motor GND is a kind of vehicle Chassis GND.

Both case will be happened, ECU GND > Chassis GNG, ECU GND < Chassis GND.

(I guess it affect negative surge protection diode, etc).

They will not put low side Rsense for current measuring.

Now, They are asking about the influence of such GND level difference on DRV8703-Q1.

Sorry to disturb your job suddenly. Please give your advice.

1. I suppose no influence on DRV8703-Q1 basic function because these are based on

    ECU GND. I wonder my guess is correct?

2. I suppose no influence on DRV8703-Q1 protection function because VDS monitor is

    executed by voltage difference, not absolute voltage level from GND.

    I wonder my guess is correct?

3. I suppose there was an influence on Gate charge because VDS would be shifted.

    I wonder my guess is correct?

4. This is related to above #3.

    I wonder VGS(th) would get the influence? Is there a possibility FET turn-on or

    turn-off was obstruced due to such influence?

Best Regards,

H. Sakai

  • 0
    TI__Guru** 114905 points
    Hi Sakai-san,

    Please clarify the connections "They will not put low side Rsense for current measuring."

    What is connected to SL2, SP, and SN (ECU GND or MOTOR GND)?
    What is connected to the two GND pins and thermal pad (ECU GND or MOTOR GND)?
  • 0 in reply to Rick Duncan
    Mastermind 6250 points

    Dear, Rick-san. 

    Thank you so much for your reply and so sorry for my duplicated sending. 

    These are brief of the connection ;

    SL2 is connected to Low-side NMOS FET's source as Figure41. 

    SP is connected to MOTOR GND. 

    SN is connected to MOTOR GND

    SO is open(not used). 

    REF is connected to AVDD(not utilized MODE1: Independent PWM control). 

    All GND pins on DRV8703-Q1 are connected to ECU GND. 

    Thermal PAD is connected to ECU GND. 

    I am expecting your help at this time. 

    Best Regards, 

    H. Sakai

  • 0 in reply to hideyuki sakai
    TI__Guru** 114905 points
    Hi Sakai-san,

    Thank you for the information.

    1. I suppose no influence on DRV8703-Q1 basic function because these are based on

    ECU GND. I wonder my guess is correct?

    >>> Correct, the basic function should operate.

    2. I suppose no influence on DRV8703-Q1 protection function because VDS monitor is

    executed by voltage difference, not absolute voltage level from GND.

    I wonder my guess is correct?

    >>> The VDS monitors should operate properly as you stated.
    >>> There are a couple of monitors that can be affected by the the GND mismatch. Please note the V(sp_ocp) specification. If the MOTOR GND increases to >0.8V above ECU_GND, an overcurrent event could occur. Also if SL2 increases to >0.8V above ECU_GND, an overcurrent event could occur.

    3. I suppose there was an influence on Gate charge because VDS would be shifted.

    I wonder my guess is correct?

    >>> You are correct.

    4. This is related to above #3.

    I wonder VGS(th) would get the influence? Is there a possibility FET turn-on or

    turn-off was obstruced due to such influence?

    >>> Yes, VGS(th) could be influenced. Turn on could be delayed if MOTOR GND increases with respect to ECU_GND. There is a possibility of FET turn-on if MOTOR GND drops with respect to ECU GND.