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Quiescient current multplied by hundreds when in drop-out zone

Thibault Lestavel1
Prodigy 60 points

Hi,

I have a design where a 3.3V LDO is directly connected to a Lithium Ion battery in an embedded device. The device will be used 2min per day so quiescient/idle current is key. 

The issue is that when the LDO input voltage is close to its supposed output voltage (LDO drop-out zone), the quiescient current is skyrocketting: The EN pin is tied to the battery voltage.I also tried with a competitor reference, I do have the same behavior:

Vbattery (Vin) Ibat (Iin)
TLV75533
2.8V 136µA
3.0V 146µA
3.2V 154µA
3.4V 22µA
3.6V 22µA
COMPETITOR
2.8V 209µA
3.0V 222µA
3.2V 273µA
3.4V 1.7µA
3.6V 1.7µA

  1. I feel like I'm missing something about the inner element inside the LDO that is leaking out in such condition, can you enlight me?
  2. Is there alternative LDO architecture that can be suitable for my application ? (relatively low Iq from 2.8V to 4.2V)

Thanks,

Thibault

  • 0
    TI__Guru 50090 points

    Hi Thibault,

    Most LDO's do this when in drop-out. In Drop-out the LDO is working hard to regulate, VOUT, but it can't. How much load current do you require? The reason I am asking is we do have the TPS7A02 which is a much lower IQ LDO, but not capable of the same peak load current.

    Please share your peak load current and I will see if I can recommend something better,

  • 0 in reply to JCHK
    Prodigy 60 points

    Hi JCHK,

    I'm supposed to power a BLE chipset so peak current is lower than 200mA.

    There is a significant price difference between "regular" low Iq LDO and the one you are proposing.

    Moreover, I still do not understand what element inside the LDO is causing such increase and if there would be any mean to bypass it.

    Thanks for your reply

  • 0 in reply to Thibault Lestavel1
    TI__Guru 50090 points

    Hi Thibault,

    This is common with most LDO's as when operating in drop-out they need to minimize over-shoot if there is a step increase on VIN. For example, if the device is plugged in to be charged, the LDO needs to make sure that this voltage does not pass straight through to the load. 

    A slightly cheaper super low IQ LDO is the TPS7A03. Here is the behavior of IQ in drop-out:

    Do you think this can work?