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CC3100MOD power supply with taps65720

dong andy
Prodigy 205 points
Other Parts Discussed in Thread: CC3100, TPS65720, LP8340, TPS63000

Hi,

 I am working on PMIC for CC3100 mod and MCU. 

The power source is Lilon battery. The tps65720 has a good performance but the WIFI module(CC3100 MOD) need about 1A current.

So can I use the followings circuit ? Which one? 1->3 or 2->3?

 

  • 0
    TI__Genius 16870 points
    Hi,

    LP8340 is an LDO so it cannot boost the voltage up to 3.3V if the VIN drops below the (minimum dropout of the LDO + 3.3V). Thus, you need to ensure that the VIN is above 3.3V + dropout requirement.

    If running off of a 1S battery the VSYS will follow the battery when no AC VIN is supplied. This means the VSYS can drop to a low voltage < 3V. (depends on your operating range of your battery) In the event that you are operating off of a 1S battery the LP8340 cannot be used for 3.3V output.

    A 3.3V output from a 1S battery requires the use of a non-inverting buck-boost converter, like TPS63000 or similar. The DC input current when in boost mode will be higher than the DC output current. Therefore, supplying the buck-boost from the DCDC1 or VSYS on the TPS65720 is not capable of 1A output from the 3.3V buck-boost because the max Iout of VSYS and DCDC1 is 400mA. Thus, you will need to operate the buck-boost directly from the battery.

    If you are not using the battery input on TPS65720:
    If you never operate off of a 1S battery then, it is possible to keep the DCDC1 or VSYS above 3.3V + dropout. This would mean that you only have to step-down the voltage from the VSYS or DCDC1 to the 3.3V rail. However, an LDO's input current matches that of the output current so, 1A out means the input must be able to supply 1A in. Neither DCDC1 nor VSYS can do this much current therefore, an LDO would be recommended or if an LDO is used it should be powered directly from the AC input supply.

    A buck is recommended for use over an LDO due to the high current of 1A draw at the load. To calculate the input current to the BUCK that is needed for 1A output, assume an efficiency and use the equation: Iin = (Vout * Iout) / (Vin * n) where n is efficiency, Vout = 3.3V, Iout = 1A, and Vin = VSYS voltage in AC powered mode or VIN to the buck if supplied from something other than TPS65720. Use VSYS over DCDC1 here because the higher voltage of VSYS will reduce the required input current.