BQ25703A Datasheet, PDF (24/81 Pages) Texas Instruments – I2C Multi-Chemistry Battery Buck-Boost Charge Controller With System Power Monitor and Processor Hot Monitor

bq25703A
SLUSCU1 – MAY 2017
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8.3.5 Current and Power Monitor
8.3.5.1 High-Accuracy Current Sense Amplifier (IADPT and IBAT)
As an industry standard, a high-accuracy current sense amplifier (CSA) is used to monitor the input current
during forward charging, or output current during OTG (IADPT) and the charge/discharge current (IBAT). IADPT
voltage is 20× or 40× the differential voltage across ACP and ACN. IBAT voltage is 8x/16× (during charging), or
8×/16× (during discharging) of the differential across SRP and SRN. After input voltage or battery voltage is
above UVLO, IADPT output becomes valid. To lower the voltage on current monitoring, a resistor divider from
CSA output to GND can be used and accuracy over temperature can still be achieved.
• V_(IADPT) = 20 or 40 × (V_(ACP) – V_(ACN)) during forward mode, or 20 or 40 × (V_(ACN) – V_(ACP)) during reverse OTG
mode.
• V_(IBAT) = 8 or 16 × (V_(SRP) – V_(SRN)) during forward mode.
• V_(IBAT) = 8 or 16 × (V_(SRN) – V_(SRP)) during forward mode, or reverse OTG mode.
A maximum 100-pF capacitor is recommended to connect on the output for decoupling high-frequency noise. An
additional RC filter is optional, if additional filtering is desired. Note that adding filtering also adds additional
response delay. The CSA output voltage is clamped at 3.3 V.
8.3.5.2 High-Accuracy Power Sense Amplifier (PSYS)
The charger monitors total system power. During forward mode, the input adapter powers system. During
reverse OTG mode, the battery powers the system and VBUS output. The ratio of PSYS current and total power
K_PSYS can be programmed in REG0x31[1] with default 1 μA/W. The input and charge sense resistors (RAC and
RSR) are programmed in REG0x31[3:2]. PSYS voltage can be calculated with Equation 1 where IIN>0 when
adapter is in forward charging, and IBAT>0 when the battery is in discharge when the battery is in discharge.
V_PSYS R_PSYS u K_PSYS(V_ACP uI_IN V_BAT uI_BAT )
(1)
For proper PSYS functionality, RAC and RSR values are limited to 10 mΩ and 20 mΩ.
8.3.6 Input Source Dynamic Power Manage
Refer to Input Current and Input Voltage Registers for Dynamic Power Management.
8.3.7 Two-Level Adapter Current Limit (Peak Power Mode)
Usually adapter can supply current higher than DC rating for a few milliseconds to tens of milliseconds. The
charger employs two-level input current limit, or peak power mode, to fully utilize the overloading capability and
minimize battery discharge during CPU turbo mode. Peak power mode is enabled in REG0x33[5]. The DC
current limit, or I_LIM1, is the same as adapter DC current, set in REG0x0F/0E(). The overloading current, or I_LIM2,
is set in REG0x37[7:3], as in percentage of I_LIM1.
When the charger detects input current surge and battery discharge due to load transient, it applies I_LIM2 for
T_OVLD in REG0x33[7:6], first, and then I_LIM1 for up to T_MAX – T_OVLD time. T_MAX is programmed in REG0x33[1:0].
After T_MAX, if the load is still high, another peak power cycle starts. Charging is disabled during T_MAX,; once T_MAX,
expires, charging continues.
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