BQ25820

The TI BQ25820 is a battery charger for 1 to 14 lithium-ion cells in series, with an integrated MPPT (maximum power point tracking) input, which allows a solar panel to charge the battery directly at high efficiency. It supports charge currents of up to 20A, an input operating range of 4.4V to 70V (the input voltage regulation point is programmable up to 65V), and a reverse mode in which the battery powers the system. The chip is configured and monitored over I²C at address 0x6B.

WARNING

Please note that the BQ25820 does not act as a multi-cell manager, charge balancer, or primary battery protection device. All battery pack(s) that you connect to your circuit(s) should always have their own primary battery management systems with multi-stage protections, and fully tested and implemented first.

TI offers their bqStudio (Windows desktop app) for development, testing, and initial-register configurations for their BQ series of charge controllers. You may need to reach out for support on their TI Forums to request a BQ25820 firmware profile (file) to take advantage of their bqStudio software, and begin bench-testing with the TI BQ25820EVM, or your own circuit design.

ESPHome exposes the chip’s:

Voltage and current measurements as sensors,
Battery charge, fault and power state as binary sensors,
Decoded charge and temperature status as text sensors.

The charge current, input limits, MPPT behaviour, charge safety timers and battery temperature thresholds are all configurable.

In order to communicate with the BQ25820, you need to have an I²C component (and its requisite GPIO pins) defined in your configuration.

# Example configuration entry
bq25820:
  charge_current: 1A
  mppt_enabled: true

BQ25820 Component

The bq25820 component polls the chip and applies the charge configuration on startup. Multiple instances may be defined if the device has more than one BQ25820.

Configuration Variables

id (Optional, ID): Manually specify the ID used for code generation. Necessary if you want to define multiple instances of this component; the platforms below then pick one with bq25820_id.
i2c_id (Optional, ID): Manually specify the ID of the I²C bus if you want to use multiple I²C buses.
update_interval (Optional, Time): The interval between polling the chip. Defaults to 60s; set a shorter interval (for example 1s) for more granular battery data. With the watchdog enabled, it must be shorter than the watchdog period. It cannot be never, since the poll writes the configuration again after a charger reset.
charge_current (Optional, Current): The battery charge current. With the reference 5mΩ battery sense resistor this is 400mA to 20A in steps of 50mA; the range and step scale with bat_sns_res. When not set, the chip keeps its power-on value and the resistor on the ICHG pin sets the current.
bat_sns_res (Optional, Resistance): The battery sense (shunt) resistor, between 0.01mΩ and 10mΩ. Must match the hardware: the battery current readings and the charge and precharge current settings are scaled by it. Defaults to 5mΩ.
ac_sns_res (Optional, Resistance): The input sense (shunt) resistor, between 0.01mΩ and 10mΩ. Must match the hardware: the input current readings and input_current_limit are scaled by it. Defaults to 2mΩ.
watchdog (Optional, Enum): The period of the chip’s I²C watchdog, one of disabled, 40s, 80s or 160s. The component feeds the watchdog on every poll, so update_interval must be shorter than the period, or the configuration is rejected. If the microcontroller stops polling, the chip falls back to its power-on charge settings when the watchdog expires; the component writes the configuration again once polling resumes. true is accepted as 160s and false as disabled. Defaults to disabled.
charge_voltage (Optional, Voltage): The VFB regulation trim point, in steps of 2mV between 1.504V and 1.566V. The battery charge voltage itself is set by the external VFB resistor divider; this option only trims the regulation limit. Defaults to 1.536V.
input_current_limit (Optional, Current): The input current limit. The charger reduces the charge current to keep the input current below it. With the reference 2mΩ input sense resistor this is 1A to 50A in steps of 125mA; the range and step scale with ac_sns_res. When not set, the chip keeps its power-on value (the maximum).
input_voltage_limit (Optional, Voltage): The lowest input voltage the charger allows, in steps of 20mV between 4.4V and 65V. The charger reduces the charge current to keep the input above it. The input undervoltage and overvoltage window is set by external resistors on the ACUV and ACOV pins, not by I²C. Defaults to 4.4V.
precharge_current (Optional, Current): The current used while the battery is below the precharge voltage. With the reference 5mΩ battery sense resistor this is 250mA to 10A in steps of 50mA; the range and step scale with bat_sns_res. When not set, the chip keeps its power-on value (4A with the reference resistor).
reverse_system_voltage (Optional, Voltage): The system voltage target in reverse mode (when the battery powers the system), in steps of 20mV between 3.3V and 65V. Defaults to 5V.
charge_enabled (Optional, Boolean): Enable the charger. Defaults to true.
hiz_enabled (Optional, Boolean): Enable HIZ (high impedance) mode, which disconnects the input source; the battery then powers the system. Defaults to false.
charge_timer (Optional, Enum): The charge safety timer, one of 5h, 8h, 12h or 24h. If the battery is still charging after this time, charging stops and the charge_safety_timer binary sensor activates. Defaults to 8h.
topoff_timer (Optional, Enum): The top-off timer, one of disabled, 15m, 30m or 45m. Defaults to disabled.
ideal_diode (Optional, Boolean): Enable the ideal diode mode. Defaults to false.
mppt_enabled (Optional, Boolean): Enable MPPT on the input. Defaults to false - enable this when the input is a solar panel.
mppt_sweep_timer (Optional, Enum): How often the MPPT input sweep runs, one of 3m, 10m, 15m or 20m. Defaults to 3m.
force_mppt_sweep (Optional, Boolean): Run one MPPT sweep at startup. Defaults to false.
temp_en (Optional, Boolean): Enable the TS (temperature) input. The TS pin expects an NTC thermistor from TS to PGND with a resistor from REGN to TS; the ts_t* thresholds are rated for a 10kΩ NTC with a 10kΩ resistor. Defaults to true.
ts_t1 (Optional, Enum): One of -10C, -5C, 0C or 5C. Below this temperature, charging is disabled. Defaults to 0C.
ts_t2 (Optional, Enum): One of 5C, 10C, 15C or 20C. Below this temperature, the charge current is limited to the precharge current. Defaults to 10C.
ts_t3 (Optional, Enum): One of 40C, 45C, 50C or 55C. Above this temperature (the warm region), charging continues at the charge current with a reduced charge voltage. Defaults to 45C.
ts_t5 (Optional, Enum): One of 50C, 55C, 60C or 65C. Above this temperature, charging is disabled. Defaults to 50C.

Sensor

The chip’s voltage and current measurements are exposed as sensors. The current values are derived from the sense resistors configured above.

sensor:
  - platform: bq25820
    vbat:
      name: "Battery Voltage"
    ibat:
      name: "Battery Current"

Configuration Variables

At least one sensor must be set.

bq25820_id (Optional, ID): The ID of the bq25820 component defined above. Required only when there is more than one.
vbat (Optional): The battery voltage in V. All options from Sensor.
vsys (Optional): The system output voltage in V. All options from Sensor.
vac (Optional): The input voltage in V. All options from Sensor.
ibat (Optional): The battery current in A, positive while charging and negative while discharging. All options from Sensor.
iac (Optional): The input current in A. All options from Sensor.
temp_in_c (Optional): The battery thermistor temperature on the TS pin in °C. Requires temp_en: true and a connected NTC. The defaults match a 10kΩ NTC with a B constant of 3435 and a 10kΩ resistor. All options from Sensor, and:
- b_constant (Optional, float): The B constant of the NTC thermistor. Defaults to 3435.
- reference_resistance (Optional, Resistance): The resistance of the NTC thermistor at reference_temperature. Defaults to 10kΩ.
- reference_temperature (Optional, Temperature): The temperature at which the NTC thermistor has reference_resistance. Defaults to 25°C.
- resistor (Optional, Resistance): The resistor from REGN to TS, above the NTC thermistor. Defaults to 10kΩ.

Binary Sensor

The charge, fault and power state of the chip is exposed as binary sensors.

binary_sensor:
  - platform: bq25820
    charging:
      name: "Charging"
    charged:
      name: "Charged"

Configuration Variables

At least one binary sensor must be set.

bq25820_id (Optional, ID): The ID of the bq25820 component defined above. Required only when there is more than one.
charging (Optional): Active while the charger is charging the battery, in any phase from trickle to top-off. All options from Binary Sensor.
charged (Optional): Active while the battery is fully charged. All options from Binary Sensor.
low_battery (Optional): Active while the charger is in trickle or precharge, which means the battery voltage is below the precharge threshold. It is only reported while charging. All options from Binary Sensor.
pg (Optional): Active while the input power is good, that is present and within its operating window. All options from Binary Sensor.
reverse (Optional): Active while the chip is in reverse mode, powering the system from the battery. All options from Binary Sensor.
vac_undervoltage (Optional): Active while the input voltage is below the undervoltage window. All options from Binary Sensor.
vac_overvoltage (Optional): Active while the input voltage is above the overvoltage window. All options from Binary Sensor.
ibat_overcurrent (Optional): Active on a battery overcurrent fault. All options from Binary Sensor.
vbat_overvoltage (Optional): Active on a battery overvoltage fault. All options from Binary Sensor.
thermal_shutdown (Optional): Active while the chip is in thermal shutdown. All options from Binary Sensor.
charge_safety_timer (Optional): Active when the charge safety timer has expired. All options from Binary Sensor.
drv_supply_invalid (Optional): Active on a driver supply invalid fault. All options from Binary Sensor.

Text Sensor

Decoded status strings for the charge cycle and the battery temperature.

text_sensor:
  - platform: bq25820
    charge_status:
      name: "Charge Status"

Configuration Variables

At least one text sensor must be set.

bq25820_id (Optional, ID): The ID of the bq25820 component defined above. Required only when there is more than one.
charge_status (Optional): The charge cycle state: Not Charging, Trickle, Precharge, Fast Charge, Taper, Top-Off or Done, and Unknown for a reserved code. All options from Text Sensor.
temp_status (Optional): The battery temperature state: Normal, Warm, Cool, Cold or Hot, and Unknown for a reserved code. Requires temp_en: true and a connected NTC. All options from Text Sensor.

Full Example

bq25820:
  id: bq25820_charger
  # --- Current sensing ---
  charge_current: 3A         # leave out to keep the ICHG pin setting
  bat_sns_res: 5mΩ           # battery sense shunt resistor (0.01-10 mΩ)
  ac_sns_res: 2mΩ            # input sense shunt resistor (0.01-10 mΩ)
  watchdog: 160s             # chip falls back to defaults if not fed;
                             # must be longer than update_interval
  # --- Charge limits ---
  charge_voltage: 1.536V     # trims the VFB regulation point; the pack
                             # charge voltage is set by the external VFB
                             # resistor divider
  input_current_limit: 8A    # input (DPM) current limit
  input_voltage_limit: 40V   # input (VINDPM) regulation point
  precharge_current: 1A
  reverse_system_voltage: 3.3V
  charge_enabled: true
  hiz_enabled: false         # HIZ: disconnect the input source
  charge_timer: 12h          # charge safety timer
  topoff_timer: disabled
  ideal_diode: false
  # --- MPPT ---
  mppt_enabled: true
  mppt_sweep_timer: 10m
  force_mppt_sweep: false    # run one panel sweep at startup
  # --- Temperature ---
  # TS pin: 10k NTC from TS to PGND with a 10k resistor from REGN to TS
  temp_en: true
  ts_t1: 0C
  ts_t2: 10C
  ts_t3: 45C
  ts_t5: 50C

sensor:
  - platform: bq25820
    bq25820_id: bq25820_charger
    vbat:
      name: "Battery Voltage"
    vsys:
      name: "System Voltage"
    vac:
      name: "Input Voltage"
    ibat:
      name: "Battery Current"
    iac:
      name: "Input Current"
    temp_in_c:
      name: "Pack Temperature"
      b_constant: 3435
      reference_resistance: 10kΩ
      reference_temperature: 25°C
      resistor: 10kΩ

binary_sensor:
  - platform: bq25820
    bq25820_id: bq25820_charger
    charging:
      name: "Charging"
    charged:
      name: "Charged"
    low_battery:
      name: "Low Battery"
    pg:
      name: "Power Good"
    reverse:
      name: "Reverse Mode"
    vac_undervoltage:
      name: "Input Undervoltage"
    vac_overvoltage:
      name: "Input Overvoltage"
    ibat_overcurrent:
      name: "Battery Overcurrent"
    vbat_overvoltage:
      name: "Battery Overvoltage"
    thermal_shutdown:
      name: "Thermal Shutdown"
    charge_safety_timer:
      name: "Charge Safety Timer"
    drv_supply_invalid:
      name: "Driver Supply Invalid"

text_sensor:
  - platform: bq25820
    bq25820_id: bq25820_charger
    charge_status:
      name: "Charge Status"
    temp_status:
      name: "Temperature Status"

BQ25820

BQ25820 Component

Configuration Variables

Sensor

Configuration Variables

Binary Sensor

Configuration Variables

Text Sensor

Configuration Variables

Full Example

See Also