[FAQ] BQ25170: Configuration of Pins and Design Questions

Some useful BQ25170 FAQs

• 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 V_{IN_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 V_HOT and V_COLD 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 T_REG (125°C).
  • Thermal shutdown turns off device if IC temperature exceeds T_SHUT (150°C). Device resumes charge when temperature falls below T_SHUT 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 V_{TS_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 V_{IN_LOWV} (3V) and V_OUT + 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 V_{BAT_SHORT} (2.2 V) and LiFePO₄ voltage less than 1.2 V, output current is regulated to I_{BAT_SHORT} (16 mA) for battery short protection.
  • Charge current is limited to the precharge current level when battery voltage is above V_{BAT_SHORT}, but below V_{BAT_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 + V_DO (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

FAQ provided by Garrett Kreger.