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[FAQ] BQ25170: Configuration of Pins and Design Questions
The device can be configured to charge 1 cell Li-Ion and LiFePO using external pins. Can the configuration be changed during operation? Any other things I should note?
How does VIN OVP (input overvoltage protection) function? --- see Data Sheet (SLUSDJ8A) section 7.3.4.1
Max input voltage without damaging device is 30 V.
Device suspends charging when the input supply is above VIN_OV (6.6 V) until the voltage recovers below the input overvoltage threshold.
Device does not have IN-DPM (voltage fold back protection).
How do I use the TS pin for Battery temperature monitoring? --- see Data Sheet section 7.3.2.4
When TS pin voltage is between VHOT and VCOLD thresholds device will follow standard charge cycle. Thresholds typically correspond to 0°C to 45°C.
Voltage at the TS pin outside the operational range results in a recoverable fault. Device suspends charging until battery temperature returns to the acceptable range.
High and low thresholds can be modified using series and parallel resistors Rs and Rp between the TS pin and the NTC thermistor.
Does the IC have internal thermal regulation?
Device monitors internal junction temperature independent of TS battery temperature input pin.
Thermal regulation counteracts overheating by limiting charge current when IC temperature exceeds TREG (125°C).
Thermal shutdown turns off device if IC temperature exceeds TSHUT (150°C). Device resumes charge when temperature falls below TSHUT falling threshold of 135°C.
Does the device have a charge enable pin?
The TS pin has the additional functionality of a charge enable pin. Pull TS below VTS_ENZ (50 mV) to disable the charger.
Toggling the TS pin will reset the charge cycle and safety timer.
The charge disable function of the TS pin provides a means to turn off automatic recharge, which is part of the charging profile by default.
System will need to have a method to reenable charging when desired as device does not monitor battery voltage when disabled via the TS pin.
Can I change ISET and VSET resistor values during operation?
The ISET pin is monitored while charging and changes to R-ISET during operation will immediately change the charge current.
The VSET pin is not continuously monitored during charge, once a resistor has been detected the corresponding regulation voltage is set until a reset event occurs.
How can I monitor charge current?
Voltage developed on the R-ISET resistor maps to output current at a 300 to 1 ratio and can be monitored by an external circuit.
What are the functions of the Charging Status (STAT) Pin? --- see Data Sheet section 7.3.3.2
STAT is an open drain output with low indicating charge in progress, including automatic recharges. Optional indicator LED will be on during charge.
STAT pin will blink at 1 Hz to indicate a fault.
STAT pin in high state indicates charge complete or charge disabled.
How does the Power Good (/PG) Pin operate? --- see Data Sheet section 7.3.3.1
/PG is an open drain output; low state indicates input power is good.
Good input power is above VIN_LOWV (3V) and VOUT + 135 mV and below the input overvoltage threshold.
Does the device regulate charge current when battery voltage is low?
Li-Ion battery voltage less than VBAT_SHORT (2.2 V) and LiFePO4 voltage less than 1.2 V, output current is regulated to IBAT_SHORT (16 mA) for battery short protection.
Charge current is limited to the precharge current level when battery voltage is above VBAT_SHORT, but below VBAT_LOWV, 2.8 V for Li-Ion and 2.0 V for LiFePO4.
What is the device behavior when no battery is connected? --- see Data Sheet Figure 8-3
When no battery is connected to OUT pin the device will quickly cycle in and out of charging with output voltage equal to the VSET regulation voltage.
How can the required power dissipation within the IC be reduced?
Device acts as a linear regulator, efficiency is improved and power dissipation is reduced the closer Vout is to Vin.
Vin will need to be larger than Vout + VDO (dropout voltage) to account for voltage loss internal to the IC.
Largest required power dissipation occurs during the beginning of the fast charge phase when battery voltage is low compared to input voltage
