BQ25872 Datasheet, PDF (17/68 Pages) Texas Instruments – Battery Switch Charger

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bq25872
SLUSCQ6 – OCTOBER 2016
Feature Description (continued)
8.3.2 Battery Switch (Q1 + Q2)
The device contains an integrated 13mΩ battery switch that is capable of handling up to 7 A of current. This
battery switch can be controlled by the host via CHG_EN I²C bit. The device can be disabled, including the
battery switch and the I²C core, by pulling the EN pin low. To turn on the battery switch charger for conduction,
the EN pin must be pulled high, CHG_EN bit must be set to ‘1’, and no fault conditions must be present (unless
they have been disabled in EVENT_1_EN register). See EVENT_1 and EVENT_2 registers for a list of
faults/events. In the event of a fault/event, the battery switch will be automatically disabled, and the host will be
notified via the INT for error reporting if the corresponding event bit is unmasked in the EVENT_x_MASK
registers.
In order to ensure that the IBUS OCP threshold is not falsely tripped during turn-on of the battery switch, the
device employs a soft-start scheme where the battery switch is slowly turned to minimize the inrush current. The
rise time of VOUT is t_{ON_VOUT}.
8.3.3 Integrated 10-bit ADC for Monitoring
With the integrated 10-bit ADC of the device, the user application can monitor the voltage of VUSB, the voltage
and current of VBUS, voltage of VOUT and VUSB, and the voltage and current of the battery. The ADC is also
used for temperature reporting of the internal junction temperature, battery temperature (via external resistor
divider and NTC thermistor), and VBUS connector temperature (via external resistor divider and NTC thermistor).
The integrated ADC has a conversion time of t_{ADC_CONV} for each parameter (except IBAT_ADC which has
conversion time of 2 x t_{ADC_CONV} ). The total conversion time of all parameters (in 1-shot mode) is between 80 µs
and 140 µs. The rate at which the ADC output registers are updated depends on the settings of ADC_AVG_EN,
ADC_SAMPLES, and the parameter conversions that have been enabled in the ADC_MASK register.
To enable the ADC, the ADC_EN bit must be set to ‘1’. The ADC is allowed to operate if either V_VUSB >
VUSB_PRESENT, V_VBUS > VBUS_PRESENT or V_VOUT > VOUT_PRESENT is valid. If ADC_EN is set to ‘1’ before VUSB or
VBUS or VOUT reach their respective PRESENT threshold, then ADC conversion will be postponed until one of
the power supplies reaches their respective PRESENT threshold. If EN pin is asserted low, then ADC conversion
is not allowed.
The integrated ADC has two conversion rate options – 1-shot conversion (only one conversion) and continuous
conversion (back-to-back conversions). To select the appropriate conversion rate, the ADC_RATE bit must be
set accordingly (‘0’ for 1-shot, ‘1’ for continuous). If ADC_AVG_EN is set to ‘0’, the ADC will convert
instantaneous measurements. If ADC_AVG_EN is set to ‘1’, the average measurement of a parameter (in both
continuous and 1-shot mode) will be determined by the setting of ADC_SAMPLES. If the user reads the output
registers before the ADC averaging is complete, then the read-back value would be unchanged from the
previous converted measurement. However, the value in the register will not change during the read-back of the
register(s). If the measured signal is outside of the range of the ADC output register in question, the reported
value in the ADC will be clamped to the min/max of the range specified. When ADC_EN is changed from 1 to 0,
the ADC registers will maintain their values from the previous converted measurement.
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