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DRV8908-Q1: DRV8908 internal MOSFET body diode sink current value

Jessica Wu74
Expert 3450 points
Part Number: DRV8908-Q1

Hi Team,

My customer want to  use DRV8908-Q1 as below to drive a relay. The relay current is about 200mA. Customer would use the internal half bridge as low side. and they want to check what is the maximum current for the freewheeling internal body diode. Since when the low side MOSFET is off, there would has current flow throw the body diode, so customer want to check the peak current for the body diode. Could you please kindly help on this? Thank you very much for your help.

Best regards

Jie

  • 0
    TI__Genius 17178 points

    Hey Jie,

    The body diode is rated the same as the FET, in this case 1.5A if not paralleled with other channels.  The 200mA current should not be an issue.  

    The freewheel diode current should not be higher than OCP limit. However, if the motor has the possibility to become a generator when low side MOSFET is off, the excess current flowing to VM can cause VM to rise higher than abs max and cause damage to the IC.   

    Regards,

    Jacob

  • 0 in reply to Jacob Thompson
    TI__Expert 3450 points

    Hi Jacob,

    For DRV8908-Q1, customer has further question need to check, below is customer design for output, they would use 4 channel(out1,out5,out4,out6) to connect to MD, and the left channel connect 1.2K pull up resistor to VM(9V~16V). With this kind design, customer see there has open load fault, could you possible help to share some comments why there would has open fault for this design? Thank you very much again for your help to confirm.

    Best regards

    Jie

  • 0 in reply to Jessica Wu74
    TI__Genius 17178 points

    Hey Jie,

    It looks like the DRV8908 only has passive open-load detection (OLD) that detects open load prior to enabling the outputs, and it should only trigger when VOLx_LS(-) < VOLx_LS   in this case.  So the first thing I would do is measure the voltage at those two points and see if they're different for some reason.  Check section 8.3.3.5.3 Passive OLD for more details on this. 

    What is the inductance and/or resistance of the relay?  We sometimes see issues with OLD when the load has a very low inductance, and I'm wondering if the relay is low-inductance.  

    I don't see anything wrong with the diagram posted.  

    Regards,

    Jacob T