CHARGER — Battery charger

Host software enables charging through register BCHGENABLESET. Battery charging starts when VBUS voltage is present and higher than VBAT by at least VBUS_VALIDR. Charging stops in case VBUS-VBAT is less than VBUS_VALIDF either because VBUS drops or VBAT rises. Once charging has started, host software must use register EVENTSBCHARGER0CLR to initialize battery charger events.

When charging is enabled, charging will not start if the battery voltage is less than VBAT_LOW. Charging batteries with a voltage lower than VBAT_LOW is enabled by setting register BCHGVBATLOWCHARGE. When charging starts, it enters trickle charging. Constant current charging starts when the battery voltage is above V_{TRICKLE_FAST}. After the battery voltage reaches V_TERM, the charger enters constant voltage charging. The battery voltage is maintained while monitoring current flow into the battery. When the current into the battery drops below I_TERM, charging is complete. Charging is disabled using register BCHGENABLECLR.

If charging is enabled on a fully charged battery, up to 100 ms of trickle charge and up to 4 ms of constant current charging is applied.

V_TERM is configured through TWI according to the battery type in use, see register BCHGVTERM.

For a higher battery temperature range, a lower termination voltage (V_TERMR) is available and configured separately in register BCHGVTERMR. V_TERM and V_TERMR can be set to the same value.

The charge current limit is set between 32 mA and 800 mA in 2 mA steps. Charging current I_CHG is configured with TWI with a default value of 32 mA.

CHARGER must be disabled before changing the current setting in registers BCHGISETMSB and BCHGISETLSB. The setting takes effect when charging is enabled.

The charge current is configured using a 9-bit value. The following shows how the register value for BCHGISETMSB can be calculated, where I_CHG is the charge current in mA:

The following shows how the register value for BCHGISETLSB can be calculated, where I_CHG is the charge current in mA:

Some example charging currents are found in the following table.

Trickle charging current, I_TRICKLE, is 10% of I_CHG. Trickle charging is active when VBAT < V_{TRICKLE_FAST} (default 2.9 V).

Termination current, I_TERM, is programmable to 10% (default) or 20% of I_CHG. Termination current is active in the constant voltage phase of charging. Charging stops when the charging current reaches this value.

These parameters are configured in registers BCHGVTRICKLESEL and BCHGITERMSEL.

CHARGER supports three types of NTC thermistors for battery temperature (T_BAT) monitoring. Only one can be enabled at a time.

The host software must select the corresponding setting that matches the battery thermistor before enabling charging in register ADCNTCRSEL. The following thermistor resistors are supported.

If a thermistor is not used, the NTC pin must be tied directly to ground or through a resistor. The functionality must be disabled in register BCHGDISABLESET. This does not impact Charger thermal regulation.

The following battery temperature thresholds can be set: T_COLD ≤ T_COOL ≤ T_WARM ≤ T_HOT.

These limits can be set between −20°C and +60°C, and setting adjacent thresholds to identical values is allowed. For example, setting T_WARM = T_HOT means that there is no warm region. Charging does not happen below T_COLD or above T_HOT. Charging can be paused at T_WARM instead of T_HOT by setting register BCHGCONFIG.

The thresholds are written into corresponding registers. The battery temperature variable, K_NTCTEMP, is calculated using the following equation:

Here, R_T is the thermistor resistance at a desired temperature and R_B (internal bias resistor) equals the thermistor resistance at 25°C. See NTCCOLD, NTCCOOL, NTCWARM, and NTCHOT for more information. Default values in the registers match the JEITA guideline and are intended for the 10 kΩ thermistor defined in Supported thermistor resistors.

The charging current can be reduced by 50% between NTCCOLD and NTCCOOL. The termination voltage can be configured independently between NTCWARM and NTCHOT. Default is I_COOL (50% of I_CHG), but this can be disabled.

Battery temperature is measured by the on-chip System Monitor at regular intervals during charging. The latest result is available in registers ADCNTCRESULTMSB and ADCGP0RESULTLSBS.

When the battery temperature rises over T_WARM or T_HOT, or falls below T_COOL or T_COLD, an interrupt is sent.

Heat dissipation from the linear charger is managed by setting a maximum temperature limit for the die. This limit must not exceed device and PCB temperature requirements.

To enable automatic thermistor and die temperature monitoring during charging, set register TASKAUTOTIMUPDATE. This should also be set after setting the automated period.

Die temperature monitoring has a default limit of T_CHGSTOP. Charging stops when the die temperature reaches the limit. It resumes when the die cools down to T_CHGRESUME.

T_CHGSTOP controls the junction temperature rise and limits the temperature rise on the PCB and device mechanics. The device can be configured to send an interrupt when the limit is met.

The die temperature variable, K_DIETEMP, is calculated with the following equation:

Here, T_D represents the die temperature limit in degrees Celsius.

Registers DIETEMPSTOP and DIETEMPSTOPLSB are concatenated to create a 10-bit value that defines the charging stop temperature T_CHGSTOP. Registers DIETEMPRESUME and DIETEMPRESUMELSB are concatenated to create a 10-bit value that defines the charging resume temperature T_CHGRESUME. The host software reads register DIETEMPSTATUS to determine if the die temperature is above T_CHGSTOP.

A CHARGER error condition occurs when one of the following are present:

• Trickle charge timeout, see t_OUTTRICKLE
• Safety timer expires, see t_OUTCHARGE

After an error is detected, charging is disabled. The charging error indication is activated and the charging indication is deactivated. Error conditions are cleared when VBUS is disconnected and reconnected again.

Errors are reported in register BCHGERRREASON and BCHGERRSENSOR. Host software clears errors with register TASKCLEARCHGERR and releases the charger from the error state with register TASKRELEASEERR.

When the safety timer expires, the host must make sure it is safe to charge before resetting register TASKCLEARSAFETYTIMER.

When CHARGER is enabled and the LEDs are configured, the LEDs indicate the charging status.

The LED[n] pins sink 5 mA of current when active. They are high impedance when disabled. This is suitable for driving LEDs or connecting to host GPIOs in a weak pull-up configuration. The LED anode must be connected to a voltage rail that allows forward bias. If a general purpose open drain output is needed, the LED pins can be used with a pull-up resistor connected to a voltage rail. See LEDDRV — LED drivers for more information.

Charging terminates automatically when the battery voltage reaches V_TERM and charging current is less than I_TERM. An interrupt is issued to the host.

Unless disabled through bit DISABLE.RECHARGE, charging restarts automatically when VBAT is less than V_RECHARGE and an interrupt is sent to the host.

CHARGER manages battery current flow to maintain VSYS voltage.

The battery is isolated when VBUS is connected and the battery is fully charged. Under this condition, VBUS supplies VSYS. When VBUS is disconnected, VSYS is supplied by its decoupling capacitors until it is connected to VBAT. The connection is triggered by VSYS reaching VSYS_{BELOW_VBAT} level and is completed within t_SWITCH.

After VBUS has been connected (and debounced), VSYS is disconnected from VBAT and supplied by its decoupling capacitors until supplied by VBUS, which happens within t_SWITCH.

The system load requirements are prioritized over battery charge current when VBUS is connected and the battery is charging. During charging, if the system current load exceeds IBUS_LIM, the battery charge current decreases to maintain the VSYS voltage. CHARGER reduces the current to maintain an internal voltage of V_CHDROPOUT above the VBAT voltage. If more current is required, CHARGER enters the SUPPLEMENT state to provide current from the battery, up to IBAT_LIM.

There are two selectable levels, IBATLIM_LOW and IBATLIM_HIGH, to limit battery discharge current and optimize current measurement and fuel gauge performance.

The discharge current limit is configured through registers BCHGISETDISCHARGEMSB and BCHGISETDISCHARGELSB.

If the system load exceeds the discharge current limit, VSYS voltage drops below VSYS_POF causing the device to reset, as described in POF — Power-fail comparator.

The two discharge current settings are found in the following table.