SLAA287B December   2005  – April 2022 MSP430BT5190 , MSP430BT5190 , MSP430F1101 , MSP430F1101 , MSP430F1101A , MSP430F1101A , MSP430F1111A , MSP430F1111A , MSP430F112 , MSP430F112 , MSP430F1121 , MSP430F1121 , MSP430F1121A , MSP430F1121A , MSP430F1122 , MSP430F1122 , MSP430F1132 , MSP430F1132 , MSP430F122 , MSP430F122 , MSP430F1222 , MSP430F1222 , MSP430F123 , MSP430F123 , MSP430F1232 , MSP430F1232 , MSP430F133 , MSP430F133 , MSP430F135 , MSP430F135 , MSP430F147 , MSP430F147 , MSP430F1471 , MSP430F1471 , MSP430F148 , MSP430F148 , MSP430F1481 , MSP430F1481 , MSP430F149 , MSP430F149 , MSP430F1491 , MSP430F1491 , MSP430F155 , MSP430F155 , MSP430F156 , MSP430F156 , MSP430F157 , MSP430F157 , MSP430F1610 , MSP430F1610 , MSP430F1611 , MSP430F1611 , MSP430F1612 , MSP430F1612 , MSP430F167 , MSP430F167 , MSP430F168 , MSP430F168 , MSP430F169 , MSP430F169 , MSP430F2001 , MSP430F2001 , MSP430F2002 , MSP430F2002 , MSP430F2003 , MSP430F2003 , MSP430F2011 , MSP430F2011 , MSP430F2012 , MSP430F2012 , MSP430F2013 , MSP430F2013 , MSP430F2013-EP , MSP430F2013-EP , MSP430F2101 , MSP430F2101 , MSP430F2111 , MSP430F2111 , MSP430F2112 , MSP430F2112 , MSP430F2121 , MSP430F2121 , MSP430F2122 , MSP430F2122 , MSP430F2131 , MSP430F2131 , MSP430F2132 , MSP430F2132 , MSP430F2232 , MSP430F2232 , MSP430F2234 , MSP430F2234 , MSP430F2252 , MSP430F2252 , MSP430F2252-Q1 , MSP430F2252-Q1 , MSP430F2254 , MSP430F2254 , MSP430F2272 , MSP430F2272 , MSP430F2272-Q1 , MSP430F2272-Q1 , MSP430F233 , MSP430F233 , MSP430F2330 , MSP430F2330 , MSP430F235 , MSP430F235 , MSP430F2350 , MSP430F2350 , MSP430F2370 , MSP430F2370 , MSP430F2410 , MSP430F2410 , MSP430F2416 , MSP430F2416 , MSP430F2417 , MSP430F2417 , MSP430F2418 , MSP430F2418 , MSP430F2419 , MSP430F2419 , MSP430F247 , MSP430F247 , MSP430F2471 , MSP430F2471 , MSP430F248 , MSP430F248 , MSP430F2481 , MSP430F2481 , MSP430F249 , MSP430F249 , MSP430F2491 , MSP430F2491 , MSP430F2616 , MSP430F2616 , MSP430F2617 , MSP430F2617 , MSP430F2618 , MSP430F2618 , MSP430F2619 , MSP430F2619 , MSP430F412 , MSP430F412 , MSP430F413 , MSP430F413 , MSP430F4132 , MSP430F4132 , MSP430F415 , MSP430F415 , MSP430F4152 , MSP430F4152 , MSP430F417 , MSP430F417 , MSP430F423 , MSP430F423 , MSP430F423A , MSP430F423A , MSP430F425 , MSP430F425 , MSP430F4250 , MSP430F4250 , MSP430F425A , MSP430F425A , MSP430F4260 , MSP430F4260 , MSP430F427 , MSP430F427 , MSP430F4270 , MSP430F4270 , MSP430F427A , MSP430F427A , MSP430F435 , MSP430F435 , MSP430F4351 , MSP430F4351 , MSP430F436 , MSP430F436 , MSP430F4361 , MSP430F4361 , MSP430F437 , MSP430F437 , MSP430F4371 , MSP430F4371 , MSP430F438 , MSP430F438 , MSP430F439 , MSP430F439 , MSP430F447 , MSP430F447 , MSP430F448 , MSP430F448 , MSP430F4481 , MSP430F4481 , MSP430F449 , MSP430F449 , MSP430F4491 , MSP430F4491 , MSP430F4616 , MSP430F4616 , MSP430F46161 , MSP430F46161 , MSP430F4617 , MSP430F4617 , MSP430F46171 , MSP430F46171 , MSP430F4618 , MSP430F4618 , MSP430F46181 , MSP430F46181 , MSP430F4619 , MSP430F4619 , MSP430F46191 , MSP430F46191 , MSP430F47126 , MSP430F47126 , MSP430F47127 , MSP430F47127 , MSP430F47163 , MSP430F47163 , MSP430F47166 , MSP430F47166 , MSP430F47167 , MSP430F47167 , MSP430F47173 , MSP430F47173 , MSP430F47176 , MSP430F47176 , MSP430F47177 , MSP430F47177 , MSP430F47183 , MSP430F47183 , MSP430F47186 , MSP430F47186 , MSP430F47187 , MSP430F47187 , MSP430F47193 , MSP430F47193 , MSP430F47196 , MSP430F47196 , MSP430F47197 , MSP430F47197 , MSP430F477 , MSP430F477 , MSP430F478 , MSP430F478 , MSP430F4783 , MSP430F4783 , MSP430F4784 , MSP430F4784 , MSP430F479 , MSP430F479 , MSP430F4793 , MSP430F4793 , MSP430F4794 , MSP430F4794 , MSP430F5232 , MSP430F5232 , MSP430F5234 , MSP430F5234 , MSP430F5237 , MSP430F5237 , MSP430F5239 , MSP430F5239 , MSP430F5242 , MSP430F5242 , MSP430F5244 , MSP430F5244 , MSP430F5247 , MSP430F5247 , MSP430F5249 , MSP430F5249 , MSP430F5252 , MSP430F5252 , MSP430F5253 , MSP430F5253 , MSP430F5254 , MSP430F5254 , MSP430F5255 , MSP430F5255 , MSP430F5256 , MSP430F5256 , MSP430F5257 , MSP430F5257 , MSP430F5258 , MSP430F5258 , MSP430F5259 , MSP430F5259 , MSP430F5304 , MSP430F5304 , MSP430F5308 , MSP430F5308 , MSP430F5309 , MSP430F5309 , MSP430F5310 , MSP430F5310 , MSP430F5324 , MSP430F5324 , MSP430F5325 , MSP430F5325 , MSP430F5326 , MSP430F5326 , MSP430F5327 , MSP430F5327 , MSP430F5328 , MSP430F5328 , MSP430F5329 , MSP430F5329 , MSP430F5333 , MSP430F5333 , MSP430F5336 , MSP430F5336 , MSP430F5338 , MSP430F5338 , MSP430F5340 , MSP430F5340 , MSP430F5341 , MSP430F5341 , MSP430F5342 , MSP430F5342 , MSP430F5418 , MSP430F5418 , MSP430F5418A , MSP430F5418A , MSP430F5419 , MSP430F5419 , MSP430F5419A , MSP430F5419A , MSP430F5435 , MSP430F5435 , MSP430F5435A , MSP430F5435A , MSP430F5436 , MSP430F5436 , MSP430F5436A , MSP430F5436A , MSP430F5437 , MSP430F5437 , MSP430F5437A , MSP430F5437A , MSP430F5438 , MSP430F5438 , MSP430F5500 , MSP430F5500 , MSP430F5501 , MSP430F5501 , MSP430F5502 , MSP430F5502 , MSP430F5503 , MSP430F5503 , MSP430F5504 , MSP430F5504 , MSP430F5505 , MSP430F5505 , MSP430F5506 , MSP430F5506 , MSP430F5507 , MSP430F5507 , MSP430F5508 , MSP430F5508 , MSP430F5509 , MSP430F5509 , MSP430F5510 , MSP430F5510 , MSP430F5630 , MSP430F5630 , MSP430F5631 , MSP430F5631 , MSP430F5632 , MSP430F5632 , MSP430F5633 , MSP430F5633 , MSP430F5634 , MSP430F5634 , MSP430F5635 , MSP430F5635 , MSP430F5636 , MSP430F5636 , MSP430F5637 , MSP430F5637 , MSP430F5638 , MSP430F5638 , MSP430F6433 , MSP430F6433 , MSP430F6435 , MSP430F6435 , MSP430F6436 , MSP430F6436 , MSP430F6438 , MSP430F6438 , MSP430F6630 , MSP430F6630 , MSP430F6631 , MSP430F6631 , MSP430F6632 , MSP430F6632 , MSP430F6633 , MSP430F6633 , MSP430F6634 , MSP430F6634 , MSP430F6635 , MSP430F6635 , MSP430F6636 , MSP430F6636 , MSP430F6637 , MSP430F6637 , MSP430F6638 , MSP430F6638 , MSP430FE423 , MSP430FE423 , MSP430FE4232 , MSP430FE4232 , MSP430FE423A , MSP430FE423A , MSP430FE4242 , MSP430FE4242 , MSP430FE425 , MSP430FE425 , MSP430FE4252 , MSP430FE4252 , MSP430FE425A , MSP430FE425A , MSP430FE427 , MSP430FE427 , MSP430FE4272 , MSP430FE4272 , MSP430FE427A , MSP430FE427A , MSP430FG4250 , MSP430FG4250 , MSP430FG4260 , MSP430FG4260 , MSP430FG4270 , MSP430FG4270 , MSP430FG4616 , MSP430FG4616 , MSP430FG4617 , MSP430FG4617 , MSP430FG4618 , MSP430FG4618 , MSP430FG4619 , MSP430FG4619 , MSP430FG477 , MSP430FG477 , MSP430FG478 , MSP430FG478 , MSP430FG479 , MSP430FG479 , MSP430FW423 , MSP430FW423 , MSP430FW425 , MSP430FW425 , MSP430FW427 , MSP430FW427 , MSP430FW428 , MSP430FW428 , MSP430FW429 , MSP430FW429 , MSP430G2001 , MSP430G2001 , MSP430G2101 , MSP430G2101 , MSP430G2102 , MSP430G2102 , MSP430G2111 , MSP430G2111 , MSP430G2112 , MSP430G2112 , MSP430G2121 , MSP430G2121 , MSP430G2131 , MSP430G2131 , MSP430G2132 , MSP430G2132 , MSP430G2152 , MSP430G2152 , MSP430G2201 , MSP430G2201 , MSP430G2201-Q1 , MSP430G2201-Q1 , MSP430G2211 , MSP430G2211 , MSP430G2212 , MSP430G2212 , MSP430G2221 , MSP430G2221 , MSP430G2231-Q1 , MSP430G2231-Q1 , MSP430G2232 , MSP430G2232 , MSP430G2252 , MSP430G2252 , MSP430G2302 , MSP430G2302 , MSP430G2312 , MSP430G2312 , MSP430G2332 , MSP430G2332 , MSP430G2352 , MSP430G2352 , MSP430G2402 , MSP430G2402 , MSP430G2432 , MSP430G2432 , MSP430G2452 , MSP430G2452 , MSP430L092 , MSP430L092

 

  1.   Trademarks
  2. 1Introduction
  3. 2Measurement Circuit
  4. 3Software
    1. 3.1 Main
    2. 3.2 ADC ISR
    3. 3.3 Watchdog Timer ISR
    4. 3.4 Software Flowchart
  5. 4Conclusion
  6. 5References
  7. 6Revision History

1 Introduction

Li-ion is the chemistry of choice for portable applications, because of its high capacity-to-size ratio and a low self-discharge characteristic. Methods to implement battery charging solutions include options such as power management ICs, MCU controlled, and even logic devices. Advantages of the MCU-controlled charging method include safe charging, time efficiency, and low cost.

Battery capacity (C), expressed in milliamp-hours (mAh), is a measure of battery life between charges. Battery current has the units of C-rate. For example, for a 500 mA-h battery, the current corresponding to 1C is 500 mA and the current corresponding to 0.1C is 50 mA.

A Li-ion battery charging process can include three stages:

  • Slow charge: Precharging stage using a current of 0.1C
  • Fast charge: Constant current charging stage using a current of 1C
  • Constant voltage charging stage

During the slow charge stage, the battery is charged with a constant low charge current of 0.1C if the battery voltage is below 2.5 V. If some batteries, like NiCd, are recharged without fully discharging, they suffer from a phenomenon called memory effect, which causes a reduction in the battery capacity. Li-ion batteries do not suffer from memory effect and do not need to be fully discharged before recharging. The slow charge stage is rarely used during the charging process of a Li-ion battery.

The fast charge (constant current) and constant voltage charging are the most important stages during a recharge process. Most Li-ion batteries have a fully charged voltage of 4.1 V or 4.2 V. The battery is first charged with a constant current of 1C until the battery voltage reaches 4.1 V or 4.2 V. The firmware continuously checks the charging current by sensing the voltage at the current sense resistor (Rsense) and adjusting the duty cycle of the PWM output from the MCU. The battery voltage is checked frequently. When the battery's voltage reaches 4.1 V or 4.2 V, the charger switches to constant voltage charging mode.

The battery is then charged with a constant voltage source at a fixed battery voltage of 4.1 or 4.2 V. The battery voltage is checked and maintained at 4.1 V by controlling the duty cycle of the PWM output. During this process the charging current starts to fall due to internal cell resistance. When the charging current falls below 0.1C, the charging process must stop.

GUID-F272BD3C-D48C-4C93-B110-7326AD20C7D4-low.gif Figure 1-1 Current vs Voltage Curve for Li-ion Battery Charging

If charging continues when the battery is fully charged, most of the electrical energy is converted to thermal energy. Overcharging batteries can cause overheating or explosion due to outgassing of the electrolyte and can severely reduce battery life. Li-ion batteries are extremely sensitive to overcharging, and it is critical that the final voltage be controlled to within ±50 mV of 4.1 V or 4.2 V. A battery charger design must be able to determine a fully charged battery to avoid overcharging. A few methods to determine a fully charged condition are:

  • When the current drops to 0.1C during the constant voltage charging stage, the battery can be considered as fully charged.
  • Measure the battery temperature to avoid overheating.
  • Safe timing method: If the charging time is longer than a predetermined time, the battery can be considered as fully charged.