Drop in replacement Li-Ion Battery Charger IC - Page 1
Forum section: electronics / projects

author: Kuusou
author_rank: Regular Contributor
timestamp: February 11, 2021, 07:29:34 am
content: I was hoping someone would be able to clear up a few questions/concerns I have about replacing anMCP73831T-2ACI_OTwith aLN2054.Below is my schematic for my current layout using the MCP73831T-2ACI_OT.The pins of both chips match, however I'm not sure whether the led indicator system I'm currently using will work with the LN2054. Currently the yellow led lights up during charging, and when complete turns off and instead the green led is lit up.The datasheet for the MCP73831T-2ACI_OT states that:"STAT is an output for connection to an LED for chargestatus indication. Alternatively, a pull-up resistor can beapplied for interfacing to a host microcontroller.STAT is a tri-state logic output on the MCP73831 andan open-drain output on the MCP73832."The LN2054 datasheet reads:"Open-Drain Charge Status Output. When the battery is charging, the CHRG pin is pulled low by an internalN-channel MOSFET. When the charge cycle is completed, a weak pull-down of approximately 20µA is connected to theCHRG pin, indicating an “AC present” condition. When the LN2054 detects an under voltage lockout condition, CHRG isforced high impedance."If I understand correctly a tri-state pin means that it can either go low or high or become high impedance, and that the LN2054 datasheet is essentially saying the same thing of its status pin as well. Is this correct? Will this still work as intended? As far as I can tell there shouldn't be any issues but I would like confirmation from a second set of eyes.My last question is regarding the PROG pin, for the MCP73831T-2ACI_OT. I'm using a 2k resistor, however in the LN2054 datasheet it states:"Charge Current Program, Charge Current Monitor and Shutdown Pin. The charge current is programmedby connecting a 1% resistor, RPROG, to ground. When charging in constant-current mode, this pin servos to 1V. In allmodes, the voltage on this pin can be used to measure the charge current using the following formula:IBAT = (VPROG/RPROG) * 1000"What does it mean by a 1% resistor? Will the same 2k resistor I was using before be sufficient? In the LN2054 datasheet on page 5 under the electrical characteristics table, the 'BAT pin Current' section appears to list a 2k resistor as the value needed so that it charges between 465 and 535 mA. I just wanted to make sure this is correct and that the resistor value of 2k would also work for the LN2054 IC.Any help is very much appreciated.

author: tooki
author_rank: Super Contributor
timestamp: February 11, 2021, 06:39:21 pm
content: I don’t mean any disrespect, but if you don’t know what “1%” means in the context of a resistor, your electronics skill level is not yet where it needs to be to safely work on Li-ion charging circuits. If you get something wrong, there’s a significant risk of fire. I hope you’ll take a step back and work on other, safer stuff for the moment.

author: tooki
author_rank: Super Contributor
timestamp: February 11, 2021, 06:55:24 pm
content: As for the LEDs, no, the open-drain chip won’t illuminate to indicate a complete charge, as there’s no path for current for the green LED. You’d have to modify the circuit with a pull-up resistor. Look at the table on page 15 of the Microchip datasheet: the open-drain variant has no condition where the output is pulled high. But without a true tri-state output, there’s no way to have either the yellow LED or the green LED or neither to turn on; with the open-drain, you can choose any two of those, but not all three.

author: mvs
author_rank: Frequent Contributor
timestamp: February 11, 2021, 07:19:03 pm
content: Quote from: Kuusou on February 11, 2021, 07:29:34 amNo, it is not correct. Tri-state output can sink current, source corrent and be disabled. Open-Drain output has only 2 states. It can sink current and be disabled.If you replace MCP73831 with MCP73832 or LN2054 green LED will not work.QuoteIt is a resistor with +/-1% tolerance. This resistors are a bit more expensive then general purpose 5% resistors.

author: Kuusou
author_rank: Regular Contributor
timestamp: February 11, 2021, 07:53:21 pm
content: Quote from: tooki on February 11, 2021, 06:39:21 pmThis circuit is copied from an Adafruit Powerboost 1000c so I'm not exactly building this from scratch. I do appreciate the concern, I'm asking on this forum before doing anything to make sure everything is correct.

author: tooki
author_rank: Super Contributor
timestamp: February 13, 2021, 03:18:54 pm
content: It’s not even the same charger IC, so you are, in essence, building from scratch.