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TPS61176 driver is not driving LCD backlight ?

Deebak Chandar1
Prodigy 130 points
Other Parts Discussed in Thread: TPS61176

Dear all,

            we used TPS61176 in our design to drive the LCD, TPS61176 is designed to generate 26.4V and ISET pin is set for 20mA. But at the output SW pin we are getting only 3.69V, we are applying input of 3.8V.

           LCD backlight comes up for few seconds when PWM/EN pin is high, after few seconds LCD turning off that time PWR/EN pin goes low.

           Also wepulled to high directly to the PWR/EN and tried but only one flicker comes when it boots. We are doubting that, IC going to shutdown mode. Anybody faced this problem ?

           In PWR/EN pin is this mandatory to apply PWM signal only because we tried with pulling it to high as well.

            These are all the following voltages at all the pins of TPS61176.

Pin1 PWM/EN 0
Pin2 VLDO 3.3
Pin3 ISET 1.1
Pin4 COMP 0
Pin5,pin6 IFB6,IFB5 1.12
Pin7,Pin9 IFB4,IFB3 0.9
Pin10,Pin11 IFB2,IFB1 0.8
Pin12 OVP 0.28
pin8,pin13 GND 0
Pin14,Pin15 SW,VIN 3.69

Can anybody help us where we are going wrong ?

Thanks & Regards,

Deebak chandar T

  • 0
    TI__Prodigy 520 points

    When the PWM signal is pulled low for more than 20ms, the IC is disabled and enters into shutdown mode. So I will suggest you pull the PWM/EN pin high with a constant logic high signal.

    If it still can't start up, please check with the waveforms in OVP and IFBX. I'm wondering that the OVP is triggered. If there's no LED string open, then smaller value for R79 will be better.