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TPS65132: OUTN Output capability of TPS65132W

Part Number: TPS65132

Hi, 

We are using TPS65132W to supply LCD panel for +6V and -6V bias voltage, as the LCD specification, it consumes 70mA maximum for both +6V and -6V in all white screen condition.

 

As the waveform below, when LCD panel is supplied by 2 external LDOs in all white screen condition, the peak current is 79.2mA (Average around 50mA), it looks current consumption is similar to specification.  

But, as the waveform below, the LCD panel is supplied by OUTN of TPS65132 in all white screen condition, the peak current is around 110mA (Average around 56mA) and more than TPS65132 output capability.

1. Why there is different behavior compared to supplying by LDO? 

2. Is there any side effect if a higher flying cap is used?

3. According to datasheet, the OUTN output capability is 80mA, it is average or peak?

Thanks,

Sam

  • Hello Sam,

    The higher peak current you see is likely due to inherent switching action of the negative charge pump on top of any peaks that are normal operation of the LCD panel.

    80mA specification of VNEG output is average current and higher peaks of small duration are not a problem.

    Kind Regards,

    Liaqat

  • Hi Liaqat,

    "80mA specification of VNEG output is average current and higher peaks of small duration are not a problem."

    As you mentioned above, could you define what is small duration? is it quantifiable? ex. 6V 150mA 1ms is acceptable.

    Thanks,

    Sam

  • Hi Sam,

    There is no specification for peak current as it is somewhat dependent on system characteristics like capacitance at VNEG output. What happens is that if the peak current magnitude/duration is higher/longer than what device can source, output voltage will start to sag. So I would suggest to measure output voltage  in your system under worst case peak current conditions and if the output does not go out of regulation, it should be good.  As far as specification goes, we only specify average current that each rails can support.

    Kind Regards,

    Liaqat