Ultra low-power Vin regulation

[Stratofour]

Dear members,

I would like to power a Microchip PIC from a 4.2V li-ion cell. I have a few constraints on my PIC selection which direct me in the group of PIC's with a maximum supply voltage of 3.6V. (The availability of a internal clock for USB comm. is one of them, no ext. osc. is needed)

Of course the voltage exeeds the PIC's maximum ratings (Vdd.abs.max:4.0V) when the li-ion cell is fully charged.

The controller is most of the time sleeping with a 32KHz RTC osc. which consumes a rough 10uA. About 6 times a day the current consumption will rise to roughly 10mA for 4 seconds. As you can see the controller is mostly sleeping.

I would like to keep the current consumption to a absolute minimum.

The LDO's I have found expect a Iq of 50uA, which is almost 5 times the standby current the PIC consumes. A DC/DC converter isn't very efficient at these current consumptions.

Does someone know a descent Vin regulation which keeps the powerloss to a absolute minimum in comparison to the controllers consumption? I would also like to use the complete Voltage range of the li-ion (4.2v->3v)Thanks!

 

[snafflekid]

If you want to use the complete voltage range of the Li-ion battery, you need to use a buck-boost converter. You have no other choice.

Another option is to place a supercapacitor across the battery, to supply your temporary high current needs. I calculated that if you draw 10mA for 4s and accept a voltage droop of 0.1V, you need a 0.4F capacitor.

 

[keith1200rs]

Unfortunately you have created conflicting requirements. You have picked a micro with the lowest power consumption but in order to use it you need to consume extra power to convert the voltage. Using a PIC which can work at 5V with slightly higher power consumption may be a better solution than trying to use the lower power PIC and wasting the power somewhere else (in a regulator).

I guess you might be able to construct some sort of crude voltage limiter with a couple of MOSFETs but you would still waste power because it will need some resistors which themselves will consume power.

Keith.

 

[darki_]

Hi,
Maybe you could use NCP698 - 2.5uA quiescent current LDO from ON Semiconductor. These devices operate with Vin up to 6V and Vout from 1.3V to 5V
https://www.onsemi.com/pub_link/Collateral/NCP698-D.PDF
I know that TI has also some 1uA LDOs in their portfolio

Best Regards
Pawel Holeksa