This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS61322: TPS613221A with external Schottky Diode for increased output current

Part Number: TPS61322
Other Parts Discussed in Thread: TPS61099

Hello,

I am using a TPS613221A for stepping up from 2.0V to 3.3V. According to the TPS61322 family datasheet, it is possible to increase the output current capability of the design by adding an external Schottky diode. In fact, an example is given in the family datasheet, but for 5V output.

As per 9.2.1.2.2, the estimated output current for Vin=2.0V, Ilim=0.75A (min), Ilh/2=0.1A, eff=0.7 should be Iout around 276mA (max).

My question is: how much can the output current be increased (estimation) by adding an external Schottky diode? Unfortunately, the family datasheet says nothing in this regard.

Thank you!

  • Hi Jose:

    Thanks for you careful question.

    Adding a external diode is to solve the thermal issue during the heavy load.The current limit won't change with or without the diode.

  • Hi Jose:

    May I know what's your load condition? (Sorry, a little confused about your previous information.)

    If the load is not so heavy, you don't need the external diode.

  • Hello Minqiu,

    This is a very low power circuit which occasionally (several times a day) requires activating a RF transmitter, which requires about 500mA for a few milliseconds. This current is, hence, transitory. I searched for other boost converters in your portfolio, however more powerful ones require a "much" higher idle consumption, around 20uA. Any suggestion in this regard is more than welcome!

    Thank you. Your first answer makes sense, however, I am now really confused with the wording in the datasheet. It'll be great if you add some clarification notes to the datasheet in the future,

    In section 8.3.2 => "The TPS61322xx boost converter can increase the output load capacity by connecting an external schottky diode from SW pin to VOUT pin. Higher than 500 mA output current is supported for 5-V output voltage applications such as USB OTG and HDMI power supply."

    However, in the whole datasheet, it says nothing about the load sharing between the internal MOSFET and the external diode. It also says nothing about the root cause of adding the diode being increasing the thermal capability of the IC.

    Best regards,

    Jose

  • Hi Jose:

    Sorry that the datasheet is not so clear about this. TPS61322 use a PFET as high side switch, and the Rds_on is little big as the size limit. So there is a thermal risk with heavy load current. Adding a Schottky could do some help for that.

    In other hand, we don't control the load sharing between internal MOSFET and external diode. But the Schottky diode will ensure the SW-Vout smaller than 0.3V typically. And the current of inter hgih side FET could be calculated as 0.3V/1ohm=300mA. (Typically)

    As you need  low power consumption, you could have a look at TPS61099. It's ultra-low Iq device, low to 1uA. And up to 93% efficiency from 10 mA to 300 mA loadhigh efficiency.

  • Thank you Minqiu, your answer is great, very detailed and clear.

    I will take into account also the suggested part/alternative (TPS61099).

    Best regards, Jose