Battery form factor, voltage, and internal resistance are all factors that should be considered when selecting a suitable protection method. The following are typical battery types to be used in an nPM2100 application and the main considerations for each option.
1.5 V batteries
- AA and AAA alkaline batteries have very low internal resistance. This means that when installed in reverse, currents can be high and cause damage to the device or overheat the battery.
- Low voltage makes it difficult to control the protection Field-Effect Transistor (FET), especially when the battery is discharged and voltage drops.
- Low voltage makes it difficult to add a diode in series since it causes a voltage drop and reduces usable battery capacity and overall efficiency.
- LR41 and LR44 batteries have a relatively high internal resistance. When installed in reverse, this can reduce the short-circuit current which improves safety.
3 V batteries
- CR batteries typically have a relatively high internal resistance. This limits the short-circuit current, but results in lower Equivalent Series Resistance (ESR) and higher currents when physically larger higher-capacity battery form factors are used.
- Two AA or AAA batteries in series have low internal resistance and high capacity. When installed in reverse, this increases the likelihood of overheating and damage to the nPM2100 PMIC.
- Higher voltage makes the protection FET easier to control, and even a diode in series can be considered in some cases.
Summary of battery options
| Parameter | Single AA or AAA | Two AA or AAA in series | LR44 | CR2032 |
|---|---|---|---|---|
| Open circuit voltage (V) | 0.8 to 1.6 | 1.6 to 3.2 | 0.9 to 1.6 | 2.0 to 3.2 |
| ESR (Ω) | < 1 | < 2 | 15 to 20 | 10 to 80 |