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TPS786: TPS78601KTTRG3

Part Number: TPS786

I have a basic doubt. Suppose I am using TPS78601KTTRG3 to generate an output of 3.3 V and the voltage at input pin number 2 is connected to a battery of range 4.2 V (Max, when full charge) to 2.8 V (Min). Also 3.3 V is connected to many active ICs whose total current will be 435 mA. My doubt to you is that will the input current (current through pin number 2) be always greater than output current,i.e., 435 mA), when the battery discharges slowly from 4.2 V to 2.8 V.

Also note that my EN pin is connected to IN pin. So how much will be the EN current be, when the battery discharges slowly from 4.2 V to 2.8 V.

TPS78601KTTRG3
  • Hi Ameet, 

    The UVLO for TPS786 has a maximum value of 2.65V, which means for your Vin at 2.8V, the LDO is on and in dropout. During dropout, the pass-FET switch of the LDO will be on to allow current flowing from Vin to the Vout. You will have some current flowing from Vin to Ground at the same time, so the input current will be higher than your load current during the process that the battery voltage drops from 4.2V to 2.8V. 

    For voltage higher than 1.7V, the EN signal will turn on the part, so the EN will not affect the LDO running in dropout when the input voltage drops to the point it's no longer in regulation. 

    Regards, 
    Jason Song

  • Thanks for replying. But please tell how much will be the EN pin current range since I am connecting a switch to EN pin which is then connected to the same battery (2.8 V to 4.2 V) which is connected to IN pin. The switch is 0.4 VA. The link to the switch part number is given below:

    https://www.digikey.in/product-detail/en/nkk-switches/AS11CP/360-2610-ND/1051309

    The reason for asking you the EN pin current is that, whether the switch AS11CP can withstand that much current.

  • Hi Ameet, 

    Normally we would have an EN current specification at its high state, which means the current spec would be taken at a voltage higher than 1.7V. But I have noticed for this device, the EN current is taken at Ven = 0V. The EN pin leakage current is usually very smaller and in the range of nanoamps to microamps. The switch you pick should have no problem driving the EN pin. 

    Regards, 
    Jason Song