Li-ion battery charger with low status battery LED indicator

[tapasxplore]

I am using MCP73831 from microchip, Li-ion battery charger IC. I am looking for a IC which has low power indicator, built into the IC via status LED. Then I got to know about STBC08 from STmicroelectronics, it has two status LED. But it has no low battery indicator.

Its datasheet says:

1) POWER ON
Open drain. When the STBC08 detects an undervoltage lockout
condition or when the external adapter provides an input voltage
higher than 7.2 V or less than the battery voltage, POWER ON goes
to high impedance state

2)  CHRG
Open drain. This pin goes to low impedance when the STBC08 is in
pre-charge or charge mode. 

Can any one help in choosing the right IC for my application.

Design Requirement:
1) Status LED should turn ON when the battery is charging.
2) LED should turn ON when the battery is in low power mode.

Regards,

[Paul Price]

What do you mean to indicate by lighting a LED with  "low battery mode" and seemingly different,  "low battery indicator"?
These indications seemingly relate to the battery while in use in a circuit, rather than in its charging, and so are not the responsibility of a charger IC.

Adding these features to a charger IC can easily be accomplished with a cheap 8-pin MCU with an internal reference for its internal A/D and use only micropower, yet wake itself up periodically to make an accurate check of the battery voltage and indicate it with a LED. Additionally, the LED can indicate a fully charged or low-battery condition and your circuit running in low-power mode with different LED modes of being on, off or blinking in one or more patterns. With a MCU a single LED can serially display the actual battery voltage in a parsed series of numbered blinks, perhaps periodically or by pressing a multi-purposed switch for a certain length of time, and the same MCU can also be used to create a step-down converter to charge the battery as well, eliminating the charger IC.

Also, depending on the battery voltage and acceptable accuracy and your visually acceptable precision of indicating a low-battery voltage state, and in consideration of your current use requirements, a circuit can be created with maybe two transistors two LED's and about 3 to 4 resistors.

 Of course there are dedicated IC's aplenty to do this job as well.

If the voltage is >2V then a single LED or LED + PNP transistor and a LED's brightness can indicate a low-battery condition. A high-efficiency LED can give a bright indication with <1mA of current use. Using two transistors and high-valued resistors, a low-battery threshold can light a LED and further save battery use and only light the LED when the battery is low.

If you are adverse to the complexity of getting a MCU to do this job, you can also use a CMOS 555 timer and get it to slowly blink a LED by using a single PNP transistor to keep the 555 timer in a 60uA low-current state until a low-voltage threshold of the battery is detected..takes just one more transistor and a resistor or two.

[tapasxplore]

Hi Paul,

I am planning to go for STM1061 (http://www.st.com/en/reset-and-supervisor-ics/stm1061.html from ST microelectronics which is a low voltage detectors. I am not planning to use micro-controller in my circuit, hence need standalone system.

Regards,

[Peabody]

If the voltage is >2V then a single LED or LED + PNP transistor and a LED's brightness can indicate a low-battery condition. A high-efficiency LED can give a bright indication with <1mA of current use. Using two transistors and high-valued resistors, a low-battery threshold can light a LED and further save battery use and only light the LED when the battery is low.

What would a one or two-transistor circuit look like to have an LED light up when a lipo battery voltage goes below 3V?