BQ25570_14 Datasheet, PDF (24/41 Pages) Texas Instruments – Ultra Low Power Harvester Power Management IC with Boost Charger, and Nano-Powered Buck Converter

bq25570
SLUSBH2C – MARCH 2013 – REVISED JANUARY 2014
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threshold voltages for two use cases 1) when a depleted battery is attached and the charger enters cold start
and 2) when a batttery charged above VBAT_UV is attached. For the best operation of the system, the
VBAT_OK should be used to determine when a load can be applied or removed. A detailed description of the
three voltage thresholds and the procedure for designing the external resistors for setting the three voltage
thresholds are described next.
5.5V
VBAT_OV
BOOST CONVERTER OFF
VBAT_OK_HYS
VBAT_OK
VBAT_UV
VSTOR=VBAT
VSTOR
VBAT_OK
(VSTOR rising)
MAIN BOOST
CONVERTER
ON
VSTOR_CHGEN
0V
V_DIODE
VBAT
COLD START ON
VIN_DC > 330mV
time
Figure 40. Charger Operation after a Depleted Storage Element is Attached
5.5V
VBAT_OV
VBAT_OK_HYS
VBAT_OK
VBAT_UV
BOOST CONVERTER OFF
VSTOR=VBAT
MAIN BOOST
CONVERTER
ON
VBAT_OK
(VSTOR rising)
0V
Attach Storage Element
time
Figure 41. 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 is closed) and with the
VSTOR node above ground results in the PFET between VSTOR and VBAT 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 capacitance to account for
transients. If the voltage applied at VIN_DC is greater than VSTOR or VBAT then current may flow until the
voltage at the input is reduced or the voltage at VSTOR and VBAT rise. This is considered an abnormal condition
and the boost charger does not operate.
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