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TPS61081: WLED-display backlight driver - configuration calculation

Amarnath Murugadass
Intellectual 480 points
Part Number: TPS61081

Hi Team,

In the system example as stated in section 10.3.3 of the TPS61081 datasheet what will happen if the PWM signal is always On or always Off? What will be the state of the output power to the backlight during those conditions?

Also for R1 and R2 in this configuration is there any calculation need to follow to choose the values along with PWM duty cycle and Rset

Regards,

M Amarnath

  • 0
    TI__Mastermind 34231 points

    Hi Amarnath,

    In section 10.3.3, TPS61081 SS pin is connected a 80kohm resistor and another 80kohm resistor in series with controlled MOSFET. The voltage at the SS pin clamps the internal reference voltage. The soft start bias current is 5uA typically.

    Therefore, is MOSFET is not turned on, the reference voltage is 80k*5uA=0.4V. The device will regulate the FB pin voltage stable at 0.4V. So current flows from Rset is 0.4V/1ohm=0.4A. The LED strings current is also 0.4A.

    When MOSFET turns on, with same calculation approach, the LED strings current is 0.2A.