• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 64 subscribers
  • Views 770 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TLV61225 efficiency trouble at light load. Is TPS61221 a better choice?

Nick Sayer
Prodigy 40 points
Other Parts Discussed in Thread: TLV61225, TPS61221, TPS61098

I've got a product powered by a single AA battery that mostly draws something on the order of a dozen µA or so most of the time but has 35 ms load pulses of 5 mA.

I've been using the NCP1402 with great success, but it's EOL, so I'm redesigning the power supply. I built a prototype with the TLV61225. With a 1.8 volt bench supply, the NCP board draws 30 µA. The TLV61225 prototype draws 80 µA. Tripling the standby power is obviously unacceptable. I'm using a 10 µH inductor and 22 µF ceramic output filter cap.

I've ordered some TPS61221 to try. Luckily they're pin compatible. The datasheet looks promising, but are they going to be closer in efficiency to the NCP? What else can I do to improve the light load efficiency of this design?

  • 0
    Prodigy 40 points

    The TPS61221s arrived today. They're better, but only barely - still well over double the NCP1402 light-load current draw.

    I tried changing the output filter cap and inductor in various combinations, but that made almost no difference.

    Anybody have any ideas?

  • 0 in reply to Nick Sayer
    TI__Mastermind 46905 points
    The TPS61098 series have better light load efficiency, you can have a look at this device.

    at VIN=1.8V, VOUT=3.3V, IOUT=30uA condition, the input current of TPS61221 should be 70uA level.
    i don't believe the NCP device is lower than 50uA. even considering 100% efficiency, its input current will be 3V*30uA/1.8V = 50uA.

    The larger inductor or output capacitor don't help much to the light load efficiency.
  • 0 in reply to Jasper Li
    Prodigy 40 points

    The load current is far, far lower than 30 µA. It's likely on the order of 10 µA or less. The load is an ATTiny45 with a 32 kHz system clock in idle mode.

    But for 35 ms about once per second the load current will jump up to 5 mA or so. But most of the time, it's near nothing.

  • 0 in reply to Jasper Li
    Prodigy 40 points
    Would it make sense to use the TPS61098 in it's "low power" mode - with the LDO permanently disabled?
  • 0 in reply to Nick Sayer
    TI__Mastermind 46905 points
    i guess the problem may be related to measurement method because of power save mode operation. refer to this application note "www.ti.com.cn/.../slva828.pdf" about measurement of input current.

    yes. you can disable the LDO of TPS61098 if not require it to power other load in your system.