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LM3631 Setting backlight voltages?

Michael Raleigh
Expert 3245 points

Hello,

1) The BL boost ovp is set at 21 volts in the software but as we increase the brightness to the voltage (vout) it passes 21v and goes higher up to 27 V. My question is if we are setting the OVP(over voltage protection) as 21v, the backlight should not go beyond 21v otherwise it can burn the lcd panel. How do we configure this?

2)What values should we select for sel_i and sel_p. We are using 7 leds in a string and according to datasheet sel_i represents the number of leds in the string. and the inductor we are using is 10uH so what values should we use for these two. It is also stated in the datasheet that these two parameters are factory selected for optimized performance but we need to know the values for them because when we set the register 3(0x07) we need the value to add on that register.  Also what effect do these two have on the backlight voltage? 

Thanks,

  • 0
    TI__Intellectual 2140 points

    Is it possible that the the OVP threshold setting is not 21V? Bits[2:1] in register 0x07 should be set to 01. Does the OVP flag get set under the conditions you described?

    The inductor does not make a difference for P/I settings. For 10uH inductor, set bit[2] of register 0x06 to 1. The P/I settings should not need any adjustment (use default values).

    The default settings for all registers are listed in Table 1. According to the table, the default value for register 0x07 is either 0xC7 or 0xC6, depending on the state of the OTP_SEL pin.