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Original question:

DRV110: Rs value

DRV110: Current limiting resistor calculations in variable Temperature

Zeinab Ramshani
Prodigy 100 points
Part Number: DRV110
Other Parts Discussed in Thread: TIDA-01621, ,

Tool/software:

Hi,

I have couple of questions related to current limiting resistor calculations: 

1) in " TI Designs: TIDA-01621, Smart Holding-Brake Control and Diagnostics Reference Design for Servo Drives and Robotics" page.12, 

it states" IGATE_AVG of 7.5 mA," however at F=20KHZ, Vmin=30V and with SI7414DN-T1-E3, ( VGs=10V, Gate charge=16C).  I cannot follow the calculation based on the provided Excell sheet, " DRV1xx Device Parameter Selector". 

2) on the same design IAUX is close to zero since there are not many components using the regulated current beside the Solenoid. correct?

3) overall, when the Enable is used, so it might change between ON and Off, and also the Temperature might go very above the 45 C, is it better to do the calculations using the provided formula on data sheet page 12 , get the Rsmin and Rsmax,  and consider the Vzenermin and Vzenermax   according to Table.1 to get 4 sets of data for Rs

or simply using the lower half of the table.3 provided resistor values for specific input Voltage?

Thanks

  • 0
    TI__Mastermind 19860 points

    Hello,

    Are you evaluating the DRV110 on the TIDA-01621 reference design? 

    1) The gate charge of 16C seems high, is it meant to be 16uC?

    If trying to calculate the IGATE_AVG current, it can be found by multiplying the MOSFET gate charge by fPWM frequency.

    2) I'm not sure which IAUX current in the design you are referring to but yes, the solenoid is the only load supplied by the DRV110. 

    3) If toggling EN pin, then using Table 3. Recommended Resistor Values in the datasheet is recommended to select current limiting resistor values. With a Vmin=30V, it would be recommended to use 36kΩ.

    Best,

    David

  • 0 in reply to David Medis
    Prodigy 100 points

    Thanks,

    if the Temperature rises and decrease the VZ to 11 instead of 15, dose it still work?

  • +1 in reply to Zeinab Ramshani
    TI__Mastermind 19860 points

    Hi,

    Yes, the values for recommended current limiting resistor values in table 3 are with respect to the supply voltage. 

    Values such as these and more can be evaluated using the DRV110EVM. 

    DRV110EVM Evaluation board | TI.com 

    Best,

    David