BQ25872 Datasheet, PDF (24/68 Pages) Texas Instruments – Battery Switch Charger

bq25872
SLUSCQ6 – OCTOBER 2016
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Feature Description (continued)
8.3.5.7 VDROP Protection
VDROP is the voltage difference from VBUS to VOUT and can be used to monitor the health of MOSFET and
power loss of the device. There are two VDROP thresholds, VDROP alarm (VDROP_ALM) and VDROP fault
(VDROP_FLT). VDROP_ALM is an indicator (via I²C register bit and INT) to alert the host that the voltage
differential between VBUS and VOUT is higher than normal, and that the host to should take action to reduce
this drop. VDROP_OVP is a fault threshold that results in the battery switch being disabled within t_{OFF_FET} after a
deglitch time of t_{VDROP_OVP} and CHG_EN set to ‘0’ when VDROP_OVP protection is enabled. Host intervention is
required to set CHG_EN to ‘1’ to enable the battery switch again. If the VDROP_OVP or VDROP_ALM value
written to the register is greater than the max defined value for the register, then the corresponding register will
be set to the highest defined value.
If a threshold has been reached (VDROP_ALM or VDROP_OVP), the appropriate bit in the EVENT_1 register is
updated (set to ‘1’ if threshold is crossed, ‘0’ if threshold is not crossed). If the EVENT_x_MASK bit is not set to
‘1’ for the corresponding bit in the EVENT_x register, then INT will assert low to alert the host of a fault.
VDROP_ALM does not affect the state of the battery switch and only causes INT to assert low when the
threshold is crossed. VDROP_OVP does turn off the battery switch and causes INT to assert low if this threshold
is crossed. Therefore, if VDROP_ALM threshold is set higher than the VDROP_OVP threshold accidentally (user
error), then VDROP_ALM functionality is never triggered since VDROP_OVP threshold will turn off the battery
switch and assert INT low.
NOTE
The threshold of VDROP_OVP and VDROP_ALM is around 13 mV lower than the actual
setting when VDROP ADC is enabled.
8.3.5.8 VBUS Temperature (TS_BUS_FLT) and Battery Temperature (TS_BAT_FLT)
TBUS_OTP and TBAT_OTP protection is active whenever the device has a valid power supply. The purpose of
VBUS temperature is to have connector temperature monitor to improve user experience. TS_BUS and TS_BAT
both rely on a resistor divider that has an external pull-up voltage. Internally, the TS_BUS and TS_BAT pins are
clamped to 2.42 V. Place a negative coefficient thermistor in parallel to the low-side resistor. A fault on the
TS_BUS and TS_BAT pin is triggered on the falling edge of the voltage threshold (signifying a “hot”
temperature).
If the TBUS_OTP or TBAT_OTP threshold is reached, the battery switch will be disabled within t_{OFF_FET} after a
deglitch time of t_{TS_OTP} and CHG_EN is set to ‘0’. Host intervention is required to set CHG_EN to ‘1’ to enable
the battery switch again. If the TS_BUS_FLT or TS_BAT_FLT value written to the register is greater than the
max defined value for the register, then the corresponding register will be set to the highest defined value.
For TS_BUS_FLT and TS_BAT_FLT, if a threshold has been crossed, the appropriate bit in the EVENT_x
register is updated (set to ‘1’ if threshold is crossed, ‘0’ if threshold is not crossed). If the EVENT_x_MASK bit is
not set to ‘1’ for the corresponding bit in the EVENT_1 register, then INT will toggle to alert the host of a fault.
NOTE
TS_BUS_FLT will not trip when TS_BUS ADC is enabled.
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