Cell charger and LDO with minimal leakage current

[Wilson__]

Appreciate advises, pointer to information and insight for choosing cell charger chip and LDO regularor for limited size project. 

Input 5 volts from USB wall socket.  After charging done, charger chip will leak minimum current from cell. 

The LDO will step down to 3.3V for MCU which is 1 uA stop mode.  The LDO should draw around 1 uA or less. 

Wonder if traditional linear LDO or Switch Mode, MCU take 2.7V minimum which give 90% duty cycle for minimum cell 3V.  Seem SMPS need 90% or less duty cycle to work.  Any pointer to cook book for inductor size (ampere handling without magnetic core satuation) and inductance   TIA

[Peabody]

The typical single-cell lithium charger is the TP4056.  I measured one and found essentially no current flowing back through the charger when the charger is not powered.

In addition, you will have some kind of protection circuit, such as a DW01, which is always on.  I think those draw about 3uA.

The MCP1700 regulator has quiescent current of about 1.6uA.

Switch-mode regulators usually are not very efficient at very low output currents.

[jbb]

If looking for switch mode controllers, you want to search for “Low Iq” or low quiescent current regulators.

An example: https://www.ti.com/product/TPS62737

Generally, a lower max output current will also correlate with a lower Iq. So if you only need 100mA max for your project then a 0.5A buck converter is likely a better choice than a 3A buck converter. But check the quoted Iq value because they vary wildly.

A big downside of a low Iq switch mode (ie buck) converter is that it probably achieves the very low Iq by going into a pulse skipping mode. This means such a buck converter will output a LOT of voltage ripple (could easily be 100 mV)

[jbb]

Oh yes, I also suggest you come up with an estimate of what your device will draw, like “it’ll draw 100 mA for 0.1% of the time, 10 mA for 0.5% of the time and about 2 uA otherwise.”

Use this information to make models of what the proposed buck converter would do versus what a basic LDO would do.

[aldi]

If the max current draw is low (<150mA) take a look at the NCP170 series. It's my jellybean low-power LDO. The Iq is around 500nA, typical.

[Wilson__]

Many thanks.  0.5uA is great

[mariush]

May want to consider using a Lithium Iron Phosphate battery instead of regular lithium ion, as they'll have 3.2v nominal voltage and 3.65v charge / maximum voltage.

So basically you may be able to get around having to use a ldo and just run your micro from the maximum 3.65v, or maybe just have a diode drop around 0.3v from this voltage, for example a BAT30F4: https://www.digikey.com/en/products/detail/stmicroelectronics/BAT30F4/5170606

You can use cheap chargers like MCP73123 (charge voltage 3.6v) : https://www.digikey.com/en/products/detail/microchip-technology/MCP73123T-22SI-MF/2126111

[Wilson__]

Many thanks.  3.6V is fine.   Many chips are 2.7 to 3.6V.  Does it has matching DW01A protection chip? 

https://support.envistiamall.com/kb/tp4056-dw01a-microusb-5v-1a-18650-lithium-battery-dual-function-charger-board-with-protection-module/

[mariush]

A quick google search came up with Hycon HY2112  : https://www.lcsc.com/search?q=hy2112

See example circuit at page 10 : https://www.lcsc.com/datasheet/lcsc_datasheet_1810010241_HYCON-Tech-HY2112-BB_C161942.pdf

I'm sure there's others that are just as good or similar.

[Wilson__]

Any idea where to get KiCad symbol and footprint for the small 1 x 1 mm package?  Is that package good and in popular use (that overseas assembly service can handle small batch order of a few pieces)?   Why factory has NO cad?  Could it mean only for high end customer with high end pick and place machine?  I meant, they developed the chip with $$$$ and making CAD modl is minor money.

[xvr]

> Any idea where to get KiCad symbol and footprint for the small 1 x 1 mm package?

EasyEDA, https://www.ultralibrarian.com/, https://www.snapeda.com/home/
or make himself

> Why factory has NO cad?

Which one? There are MANY different cads