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TPS7A21-Q1: Ultra low Iq LDO for microamp loads

Faris AtaAllah
Prodigy 40 points
Part Number: TPS7A21-Q1
Other Parts Discussed in Thread: TPS7A02

Tool/software:

Dear TI Team,

We are currently in the final design stages of our IoT edge device and are looking for an ultra-low Iq LDO.

Our power requirements include an input voltage range of 2.5V to 5.5V, a fixed output of 3.3V, and a current rating between 500mA and 1000mA. The most critical requirement is a very low idle current (Iq).

We've encountered an issue with our current LDO. When our device enters sleep mode and the current consumption drops to 15 microamps, the LDO output rises to 3.9V instead of the regulated 3.3V. This indicates it is unable to regulate at such a low current draw.

After reviewing the TI LDO portfolio, the "TPS7A21-Q1" appears to meet our specifications. We would appreciate your expert advice on whether this part is indeed suitable for our application. Or if you recommend other options.

  • 0
    TI__Guru 50025 points

    Hi Faris,

    I have a few questions. 

    1. You mentioned the input voltage range can go down to 2.5V and up to 5.5V. What's the typical or nominal voltage? The lower limit of 2.5V will result in the device not regulating, and at the upper limit of 5.5V could present a thermal issue if it's operated near 500mA. 
    2. What is your "ultra-low Iq" requirement? Do you have a specific target or do you just need the lowest Iq you can get? 
    3. How many loads are you supplying from this power supply? Do you have any budget or board space to use more than one LDO if you are supplying multiple loads? I ask because we have the TPS7A02 which is optimized for ultra-low Iq and comes in a small package, but is only rated for 200mA.

    At first glance, it looks like TPS7A21-Q1 could work for you, but I'll need to see your responses to say with more confidence. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 40 points

    Dear Nick,

    Thank you for your reply, and apologies for any missing information.

    Regarding your questions:

    1. We are running the device using a 18650 Li-ion cell. The normal operating voltage range is between 3.4V and 5V due to having a special circuit which keeps the voltage coming from the battery in that range. The reason i said 2.5V to 5.5V is because this the typical range for the LDOs which we were looking into.
    2. We want to go down to the lower uA range (the LDO we have right now is rated for 1A and has a green operating mode which can go as low as 8 uA for Iq).
    3. We do have multiple loads, some of them are always on, while others have a sleep cycle. Budget and space constraints exist, so we would like to have a single LDO if possible. The TPS7A02 you kindly mentioned, is already in use by us for a different board, however the 200 mA limit is low for the device we are discussing with you. We would like to have at least 500 mA as the rating for the LDO.

    If you can also confirm to us if the TPS7A21-Q1 can still regulate at 10 to 15 uA load current, so we can know whether to consider it or not.

    We will also consider your suggestion about using multiple low power LDOs.

    Kind regards,

    Faris

  • +1 in reply to Faris AtaAllah
    TI__Guru 50025 points

    Hi Faris,

    Understood. TPS7A21-Q1 can regulate with no load - in fact, the quiescent current spec is at no load. So, 10uA to 15uA load is no problem. It looks to me that this device will work for your application. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 40 points

    Thank you for your help Nick, much appreciated.

    We will go with the TPS7A21-Q1 most probably.