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HS+LS FET on-resistance of DRV8835

yoshihiro hirata
Expert 1425 points
Other Parts Discussed in Thread: DRV8835

HS+LS FET on-resistance of DRV8835

My customer is considering to use DRV8835.
They have a question.

1) Do decrese HS+LS FET on-resistance of DRV8835 when they increase only VM?
     For example;
         VCC=3V, VM=3V, HS+LS FET on resistance(TYP)=370mohm (on datasheet)
         VCC=5V, VM=5V, HS+LS FET on resistance(TYP)=305mohm (on datasheer)
         VCC=3V, VM=5V, HS+LS FET on resistance(TYP)=decrese?

2) If you have some data, please provide me it.
     They will use DRV8835 with VCC=3.3V and VM=5.0V.
     So if there is this condition data made they feel thankful.

Best regards,
Y. Hirata

  • 0
    TI__Guru** 114905 points

     Hi Hirata-san,

    Please see Figure 4. Typical values for Vcc=3V, VM=5V is plotted across temp there.

  • 0 in reply to Rick Duncan
    Expert 1425 points
    Duncan-san,

    Thank you for your quick reply.

    I referred to Figure 4.
    But, I don't understand about 1) of question.
    Could you let me any advices?

    >1) Do decrese HS+LS FET on-resistance of DRV8835 when they increase only VM?
    > For example;
    > VCC=3V, VM=3V, HS+LS FET on resistance(TYP)=370mohm (on datasheet)
    > VCC=5V, VM=5V, HS+LS FET on resistance(TYP)=305mohm (on datasheer)
    > VCC=3V, VM=5V, HS+LS FET on resistance(TYP)=decrese?

    Best regards,
    Y. Hirata
  • 0 in reply to yoshihiro hirata
    TI__Guru** 114905 points
    Hi Hirata-san,

    The HS+LS on-resistance is dependent on both VM and VCC.

    Starting at 370mOhm when VCC=3V, VM=3V, high side on resistance decreases as VM increases from 3V to 5V. So the total HS+LS on resistance is ~340mOhm.
  • 0 in reply to Rick Duncan
    Guru 11215 points

    Hi Rick-san,

    Allow me to cut in.

    Our customer test the output voltage of the DRV8835.

    The test condition of the customer as follows.

    Load : 8 ohm resistor (not motor)

    VM=2V

    VCC: variable

    I attach the result file as below

    DRV8835_VOUT.pdf

    When the VCC is under 2.6V, is it possible to active completely the low side FET?

    Best Regards,

    Naoki Aoyama

  • 0 in reply to NAOKI AOYAMA
    TI__Guru** 114905 points
    Hi Aoyama-san,

    The low side FET is driven by a charge pump using VCC. The charge pump is not at max value until approximately 2.5V.

    The RDSon will be higher in this region, as shown in the attached file and figure 4 of the datasheet.

    FYI -- the high side FET has a similar charge pump that is driven by the higher voltage of VCC or VM. This can affect the measurements collected in the file.
  • 0 in reply to Rick Duncan
    Guru 11215 points
    Hi Rick-san,

    Thank you for your reply.
    I understood how to drive the FET.
    I will feedback the customer this information.

    Thanks,

    Naoki Aoyama