A Designer’s Guide to Lithium Ion (Li-ion) Battery Charger

Last Updated: January 6th, 2022 | By: Gina

There is a huge demand for great battery life in implantable medical devices and low-power consumer electronics. In turn a dire need for improved energy efficiency is conferred in the regulation of small rechargeable cells.

The following are the desegregated single-cell Li-ion or Li-polymer chargers which have the operational ability at an input voltage as low as 2.5 V.

  • ISL9205

  • ISL9205A

  • ISL9205B

  • ISL9205C

  • ISL9205D

Since they have a low operating voltage, so it allows the chargers to work with a variety of AC adapters.

Li-ion Battery Charger Detailed Guide

Key Features

  • All-inclusive charger – single-cell Li-ion/polymer batteries

  • Includes pass element & current sensor

  • Low component count& cost

  • Programmable charge current

  • Trickle charge for fully discharged batteries

  • Power presence & charge indications

  • NTC interface (unavailable in some packaged options)

  • Ambient temperature range: -40°C to +85°C

  • DFN, QFN packages

  • Pb-free (RoHS compliant)

  • 25mV voltage accuracy over-temperature & input voltage-range

  • 15mV voltage accuracy at room temperature

  • Programmable end-of-charge current (ISL9205)

  • Charge current thermal fold back for thermal protection (Therma-guard)

  • When no input power attached/charger disabled, less than 3μA leakage current off the battery


  • Mobile Phones

  • MP3 Players

  • Blue-Tooth Devices

  • PDAs

  • Blue-Tooth Devices

  • Stand-Alone Cradle or Travel Chargers

  • Other Handheld Devices

ISL9205 – This family works as a linear charger while the AC- adapter is on a voltage source. Using a standard Li-ion charge profile, the battery is charged i.e. constant current phase followed by a Constant Voltage phase (CC/CV).

During the constant current phase the charge current is determined by the external resistor connected to the IREF pin. When the current limit is less in comparison to the programmed constant current of IC and the adapter output is also a current-limited voltage source.

The ISL9205 functions as a pulse charger where during the constant current phase the charge current is intended by the AC adapter’s current limit. In both the adapter cases the ISL9205 operates using a linear mode.

This also integrates the Thermaguard- offers protection to the IC against over-temperature. For e.g. In case the die temperatures increases above a representative value of +100°C, then the thermal fold back function minimizes the charge current to eliminate the risk of further temperature rise.

The external temperature monitoring function, though unavailable in some package options is a part of the ISL9205. For monitoring the battery or ambient temperature a Negative Temperature Coefficient- NTC thermistor is connected between the TEMP pin and GND. A timer is also included in the ISL9205 fir setting the time reference for various charge time limits.

The timer sits programmable with an external capacitor. For charger control and charger status indication there are two logic inputs and two open-drain logic outputs available. The charger is enables by the EN pin.

The timeout function is enabled by the TOEN pin, this way the charges gets terminated after the pre-set time limits have reached.

When a fault condition is encountered, an open drain output – FAULT pin turns on. There is another pin – STATUS pin that automatically turns on when the charger is transferring current.

Product Options

Part Number Part Status Pkg. Type Carrier Type MOQ Buy Sample
ISL9205DIRZ Active DFN Tube 100 Buy Now
ISL9205DIRZ-T Active DFN Reel 6000 Buy Now

Documentation & Downloads

Title Type Format File Size Date
Datasheets & Errata
ISL9205, ISL9205A, ISL9205B, ISL9205C, ISL9205D Datasheet Datasheet PDF 791 KB Sep 20, 2016
Application Notes & White Papers
Five Easy Steps to Create a Multi-Load Power Solution White Paper PDF 846 KB Aug 14, 2018
AN1684: Nonideality of Ground Application Note PDF 397 KB Jan 19, 2004
AN1681: Grounding Techniques Application Note PDF 509 KB Jan 19, 2004

Boards & Kits

Part Number Title Type Company
ISL9205DEVAL1Z Li-Ion Battery Charger Evaluation Board Evaluation Renesas

Frequently Asked Questions

Q1. Do lithium-ion batteries require a special charger?

Ans1. If you have a lithium battery then you will need a CC/VV- Constant current/Constant voltage charge type along with absorption, simple bulk, and float stages. Several lead acid chargers come with in-built de-sulphating and equalisation stages. They work to pulse high-voltages of 15.3-15.8V into the battery.

Q2. Can a lithium-ion battery be overcharged?

Ans2. If overcharging is the case with your lithium-ion battery then this may result in unsteady conditions inside your battery.

There could be things such as:

  1. Increased pressure
  2. Thermal runaway
  3. Reduced capacity
  4. Shortened lifecycle

All these things will work worst for your battery causing crucial damages.

Q3. How often should I charge my lithium-ion battery?

Ans3. The estimated life of a Lithium-ion battery comes around 2 to 3 years or say around 3oo to 500 charge cycles. For this ‘whichever occurs first’ is the rule.

Over here 1 charge cycle is considered to be a time-period of use fully charged – fully discharged, and fully re-charged again.

Q4. Which is the right way to charge Lithium-ion battery?

Ans4. You should follow the following easy steps for charging a Lithium-ion battery:

  1. Firstly, disconnect the load or turn-off the device for allowing the current to drop unhampered during saturation.
  2. You should charge at a moderate temperature.
  3. You need not fully charge a lithium-ion battery as it does not need to be.
  4. Partial charging is the best.