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DRV8718-Q1: charge pump capbility

Chuqiang Wen
Expert 4830 points
Part Number: DRV8718-Q1
Other Parts Discussed in Thread: LM2902B, LM2903B

Tool/software:

Hi Expert, 

My customer use DRV8718-Q1 as 8 high side controller application. For some loads, it need 2 or 3 MOSFET in parallel, which means single DRV8718 drive up to 12 external MOSFET. 

Except that, customer also consider to use 8718 charge pump to supply external current sense amplifier--LM2902B-Q1(max supply current is 3mA, up to 6 pcs LM2902B here). 

So I would like to check with you what is the max capability of 8718 charge pump? If 8718 need to drive 12 external MOSFET, how much current is left to drive the external amplifiers? 

Thanks! 

Ethan Wen 

  • 0
    TI__Mastermind 28295 points

    Hi,

    Thank you for your questions. 

    >>If 8718 need to drive 12 external MOSFET, how much current is left to drive the external amplifiers? 

    It is a little tough question, because it depends on external FET's gate cap, switching frequency, driver current setting could impact. 

    However, this charge pump can be used for external reverse battery protection which does not consume much current. I do not recommend you to put 3mA x 6pcs LM2903B = 18mA. It is relatively high against VCP SPEC condition. 

    As quick guess, up to 5+mA range should be doable, but may have concern with ~18mA.

    regards

    Shinya Morita

  • 0 in reply to Shinya Morita
    TI__Expert 4830 points

    Hi Morita-san, 

    Thanks for your feedbacks.

    To help better estimation for customer case, may I know the max current capability of internal charge pump? 

    Regards,

    Ethan Wen

  • 0 in reply to Chuqiang Wen
    TI__Mastermind 28295 points

    Hi Ethan,

    On datasheet, PVDD>=13V with 25mA is guide line to keep 10.5V typ and 9.5V(min) . However, really is DRV has some margin. 

    I can say 30mA is acceptable.

    regards

    Shinya Morita

  • 0 in reply to Shinya Morita
    TI__Expert 4830 points

    Hi Morita-san, 

    As further discussion with customer, their FET Qg is about 55nC. These high side usecase don't require PWM operation. There have two typical configuration for their 8718 usage. 

    Configuration 1: All 8718 output are configured to high side use-case. Single 8718 drive 12 MOSFETs max. No PWM requirement. 

    Configuration 2: 6 HB of 8718 are configured to high side, 2 HB of 8718 are configured to full bridge to control 1 motor. No PWM requirement for high side, 20KHZ PWM for motor control. 

    Based on these two configurations, could you please help check how much current from internal charge pump can be used to supply external load? 

    From my understanding, if no PWM requirement, the average gate charge current will be very low. For configuration 1, can DRV8718 support external 10mA max load(3 pcs of LM2902B)? For configuration 2, 2 HB for motor drive--avg current per FET=Qg/t=1.1mA. 2 HB total avg current is about 4*1.1=4.4mA. The average current will be low for the other 6 high side configuration. Is my calculation correct?  

    Thanks!

    Ethan Wen

  • 0 in reply to Chuqiang Wen
    TI__Mastermind 28295 points

    Hi Ethan,

    Thank you for your feedback.

    I am OK if your additional load is up to 10mA by 3pcs LM2902B. As long as using charge pump triple mode, it should be doable.

    regards

    Shinya Morita