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TPS92611-Q1: Parallel resistor Rp, why it is recommended?

Dustin Yim
Intellectual 2180 points
Part Number: TPS92611-Q1

Hi Experts,

From the data sheet, I have a question about "Parallel resistor R(P) is recommended to consume 1/2 of the total current at maximum supply voltage.".

 I wonder why the Rp is needed?

The Rp connect the In pin and Out pin. 

I simulated this device with Rp (100 ohm). And also without Rp.

Please see the result.

Vsupply = 12V, I(Led) = 100mA, Vpwm = 12V & 1000Hz

- Without Rp. The output current I(D2) have no current when V(pwm) = 0 

Frist graph is PWM signal. Fourth graph is I(D2)

- With Rp. The output current I(D2) have 50mA current when V(pwm) = 0

So, I wonder why the Rp is needed?

I think 100mA on-off PWM signal is enough to light the LED.

  • 0
    TI__Genius 10606 points

    Hi Dustin,

     The Rp is for power dissipation and recommended to use when the power dissipation is too large according to this equation:

    The output LED voltage is unknown now. But considering your Vin, ILED and normally 3LEDs, the power is about 1W which would be near the TSD temperature in ambient temperature 85deg.

    With the Rp calculated like below,

    The power dissipation on the device should be decreased.

    As for PWM,

    BR, Gracie