bq24170
bq24172
SLUSAD2A –NOVEMBER 2010–REVISED NOVEMBER 2010
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CHARGE UNDER-CURRENT PROTECTION
After the recharge, if the SRP-SRN voltage decreases below 5mV, the low side FET will be turned off for the rest
of the switching cycle. During discontinuous conduction mode (DCM), the low side FET will only turn on for a
short period of time when the boostrap capacitor voltage drops below 4V to provide refresh charge for the
capacitor. This is important to prevent negative inductor current from causing any boost effect in which the input
voltage increases as power is transferred from the battery to the input capacitors. This can lead to an
over-voltage on the AVCC node and potentially cause damage to the system.
BATTERY DETECTION
For applications with removable battery packs, IC provides a battery absent detection scheme to reliably detect
insertion or removal of battery packs. The battery detection routine runs on power up, or if battery voltage falls
below recharge threshold voltage due to removing a battery or discharging a battery.
POR or RECHARGE
Apply 8mA discharge
current, start 1s timer
1s timer
expired
No
VFB < VBATOWV
No
Yes
Yes
Battery Present,
Begin Charge
Disable 8mA
discharge current
Enable 125mA charge
current, start 0.5s timer
0.5s timer
expired
No
VFB > VRECH
No
Yes
Yes
Battery Present,
Begin Charge
Disable 125mA
charge current
Battery Absent
Figure 20. Battery Detection Flowchart
22
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