8.3.21 Battery Detection

For applications with removable battery packs, the BQ24650 provides a battery absent detection scheme to reliably detect insertion or removal of battery packs.

Figure 12. Battery Detection Flowchart

When the device has powered up, a 6-mA discharge current is applied to the SRN terminal. If the battery voltage falls below the LOWV threshold within 1 second, the discharge source is turned off, and the charger is turned on at low charge current (125 mA). If the battery voltage gets up above the recharge threshold within 500 ms, there is no battery present and the cycle restarts. If either the 500 ms or 1 second timer time out before the respective thresholds are hit, a battery is detected and a charge cycle is initiated.

Figure 13. Battery Detect Timing Diagram

Take care that the total output capacitance at the battery node is not so large that the discharge current source cannot pull the V_FB voltage below the LOWV threshold during the 1 second discharge time. The maximum output capacitance can be calculated according to Equation 9:

Equation 9.

where

• C_MAX is the maximum output capacitance,
• I_DISCH is the discharge current,
• t_DISCH is the discharge time,
• and R₂ and R₁ are the voltage feedback resistors from the battery to the VFB pin.

The 0.5 factor is the difference between the RECHARGE and the LOWV thresholds at the VFB pin.