bq25505
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SLUSBJ3B –AUGUST 2013–REVISED JANUARY 2014
5.5V
VBAT_OV
BOOST CHARGER OFF
VSTOR=VBAT_SEC
MAIN BOOST
CHARGER
ON
VBAT_OK_HYST
VBAT_OK
VBAT_UV
VBAT_OK
VSTOR
VSTOR_CHGEN
0V
VDIODE
VBAT_SEC
COLD START ON
VIN_DC > 330mV
time
Figure 28. Charger Operation after a Depleted Storage Element is Attached
5.5V
BOOST CHARGER OFF
VBAT_OV
VSTOR=VBAT_SEC
VBAT_OK_HYST
MAIN BOOST
CHARGER
VBAT_OK
ON
VBAT_OK
VBAT_UV
0V
time
Attach Storage Element
Figure 29. Charger Operation after a Partially Charged Storage Element is Attached
When no input source is attached, the VSTOR node should be discharged to ground before attaching a storage
element. Hot-plugging a storage element that is charged (e.g., the battery protector PFET is closed) and with the
VSTOR node above ground results in the PFET between VSTOR and VBAT_SEC remaining off until an input
source is attached. In addition, if a system load attached to VSTOR has fast transients that could pull VSTOR
below VBAT_UV, the internal PFET switch will turn off in order to recharge the CSTOR capacitor to
VSTOR_CHGEN. See the application section for guidance on sizing the VSTOR and/or VBAT_SEC capacitance
to account for transients. If the voltage applied at VIN_DC is greater than VSTOR or VBAT_SEC then current
may flow until the voltage at the input is reduced or the voltage at VSTOR and VBAT_SEC rise. This is
considered an abnormal condition and the boost charger does not operate.
Battery Undervoltage Protection
To prevent rechargeable batteries from being deeply discharged and damaged, and to prevent completely
depleting charge from a capacitive storage element, the IC has an internally set undervoltage (VBAT_UV)
threshold plus an internal hysteresis voltage (VBAT_UV_HYST). The VBAT_UV threshold voltage when the
battery voltage is decreasing is internally set to 1.95V (typical). The undervoltage threshold when battery voltage
is increasing is given by VBAT_UV plus VBAT_UV_HYST. For most applications, the system load should be
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