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TPS43340-Q1: TPS43340-Q1 Low Power Mode

Yang Wu
Expert 3320 points
Part Number: TPS43340-Q1

Hi team,

About TPS43340-Q1's Low Power Mode, I have some questions. Could you explain when HS Switch will be turned off in Low Power Mode? 

Datasheet says [Whenever the VSENSEx value falls below the reference, the high-side MOSFET turns on for a pulse duration inversely proportional to the difference across VIN-S2 for Buck 1 and VIN-S4 for Buck2. ], how this Ton can be decided? In some TI devices, there has a min peak current limit to decide Ton, here I am still confused how Ton can be determined. 

Could you have some detailed explanation?

Thanks a lot,

Best regards,

Yang

  • 0
    TI__Genius 13850 points

    Hi Yang,

    Discontinuous mode is specified as a portion of the load current when device enters and exits to/from LPM mode.

    Datasheet has no explicit number for HSFet Ton time or current pulse level. As this depends on VIN/VOUT ratio, SW frequency and chosen external components the information of this is expressed as percentage of the load current and will vary over different applications.

    Do you have more information about application where this device will be used? VIN and VOUT and other parameters?

  • 0
    TI__Mastermind 28260 points

    Hello,

    When the inductor current hits zero crossing and both upper an lower FETS are off more than 60% of the clock cycle, the device enters in low power mode. In low power mode LPM, the error amplifier is idle and an internal hysteretic comparator is activated to regulate the output voltage. The load is very light and the output capacitor is slowly discharging. When the output voltage is below the setting level (Vfb < Vref), the hysteretic comparator turns on the upper FET. The statement in datasheet can be explained with this formula L dI/dt = Vin - Vout. Or L x Ipeak/Ton = Vin - Vout. Ton = L x Ipek/(Vin - Vout) so Ton is inversely proportional to Vin - VSx. The hysteretic comparator turns off the upper FET once the capacitor is charged and Vfb = Vref.

    Regards