Is my programmer being honest? Li-Ion charging algorithm

Thread Starter

Dhaya777

Joined Oct 20, 2014
3
I have designed a portable medical device that uses a LI-Ion battery pack (two packs of 3.4V).
Currently the battery only charges when the capacity falls below 5% of total charge.
This is a nuisance to the patient, who would like the device to charge when ever the charging adaptor
is plugged in regardless of the charge level of battery.

My programmer insists he can't change the algorithm because the IC/microchip he used in the design
doesn't allow such changes.

I contacted the company that makes the chip and this was the reply....

The VDD input is the input supply to the MCP73213. The MCP73213 automatically enters a power-down mode if the voltage on the VDD input falls to within +50 mV of the battery voltage. This feature prevents draining the battery pack when the VDD supply is not present. This device is designed to charge the device when the battery Vref reaches below a certain point.

The MCP73213 employs a constant current/constant voltage charge algorithm. The various charging voltage regulations provide design engineers flexibility to use in different applications. The fast charge, constant current value is set with one external resistor from 130 mA to 1100 mA. The MCP73213 limits the charge current based on die temperature during high-power or high ambient conditions. This thermal regulation optimizes the charge cycle time while maintaining device reliability. The PROG pin of the MCP73213 also serves as enable pin. When high impedance is applied, the MCP73213 will be in Standby mode.

https://www.microchip.com/wwwproducts/en/MCP73213

My electronics knowledge is amazingly basic, please don't hold it against me.
This device is designed to charge the device when the battery Vref reaches below a certain point. This sentence to me says that if the Vref can be changes to a higher level than the device will charge whenever a charging adapter is plugged in.
Am i being foolish?

Any help would be much appreciated.
Thank you for your time.
 

nsaspook

Joined Aug 27, 2009
8,653
My read of the datasheet is that if the PROG pin remains always connected then the auto-recharge will happen at the factor set level. However a manual recharge can be started by making the PROG pin high-Z (open) and then the PROG pin is reconnected to the programming resistance.
 

Thread Starter

Dhaya777

Joined Oct 20, 2014
3
My read of the datasheet is that if the PROG pin remains always connected then the auto-recharge will happen at the factor set level. However a manual recharge can be started by making the PROG pin high-Z (open) and then the PROG pin is reconnected to the programming resistance.
Thank you for taking the time to answer this...silly question, Is this change a software code change or a hardware redesign ?
 
Last edited:

Yaakov

Joined Jan 27, 2019
3,464
I have designed a portable medical device that uses a LI-Ion battery pack (two packs of 3.4V).
Currently the battery only charges when the capacity falls below 5% of total charge.
This is a nuisance to the patient, who would like the device to charge when ever the charging adaptor
is plugged in regardless of the charge level of battery.
It seems the chip initiates a recharge when the battery is about 95% of it's capacity (5% down). This is a battery life management tactic. Lithium batteries charge quickly (~1 hour) to 85% capacity and then take 3 times longer to reach 100%. The battery's life is extended by not constantly applying a topping charge. It is normal and expected that a good charger will not immediately begin a charging cycle if the battery is above 95% charge.
 
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