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DRV103: Computation of RPWM at other duty cycles and frequencies

Part Number: DRV103

Hi Team,

A customer wants to compute for the value of RPWM resistor for DRV103H to create a 65% duty cycle at 24kHz oscillator frequency. The closest values specified in the datasheet are for 60% or 70% at 25kHz. What is the computation for other frequencies and duty cycle?

Regards,

Danilo

  • Danilo, 

    There are a few equations we need to use to pick an arbitrary duty cycle thats not in the d/s. The duty cycle depends on Rfreq as well.  

    Rfreq calculation from F is below:

    So Rfreq~212kOhm for 24kHz. 

    IREF = 1.3V / RFREQ , RFREQ is the resistor you choose for your frequency (212K)

    IREF ~ 6.12uA. 

    Vduty is the voltage at the pin1 for duty cycle adjust

    Vduty=2.75*IREF * Rduty

    From below, we can get the linear equation for Vduty vs D%, and relate that to RDUTY  / RREF

    D%=0.392*Vpwm - 0.4944

    and from that,

    D%=0.392*2.75*IREF*Rpwm - 0.4944

    D% will be from 0.1-0.9,  btw. Multiply slope/intercept by 100 t0 get 10%-90%

    From above equation i get Vpwm=2.92V, from there we calculate Rpwm = 2.92/(2.75*IREF)= 173kOhms

     

    Hopefully this helps with design process. Note that while Vpwm vs D% is roughly linear, there is always small variability in the IC.

    If this answers your question, please let me know by pressing the green button. 

    Best

    DImitri

  • Thank you for providing me with that information. For the oscillator frequency, I chose a 210k ohm 1% resistor and for the duty cycle adjust, I chose a 174k ohm 1% resistor since they are the closest standard values.

    I have 1 more question. We are using the DRV103H which has the Power PAD. I see in the datasheet that it is internally connected to ground and they don't recommend using the power pad as the main source of ground. Can I still use the ground pin and have the power pad connected to the ground plane or do you recommend having the power pad floating to a separate piece of copper?

    Thank you,

    Steve  

  • Steve, 

    You would want to connect the GND pin and powerPad to gnd plane. powerPad should be connected to ground plane for thermals, the ground plane is used as a heatsink. 

    If this answers your question, please let me know by pressing the green button. 

    Best

    Dimitri