LT8491 no-OS driver

Supported Devices

LT8491

Overview

The LT8491 is a buck-boost switching regulator battery charger that implements a constant-current constant-voltage (CCCV) charging profile used for most battery types, including sealed lead-acid (SLA), flooded, gel and lithium-ion.

The device operates from input voltages above, below or equal to the output voltage and can be powered by a solar panel or a DC power supply. On-chip logic provides automatic maximum power point tracking (MPPT) for solar powered applications. The LT8491 can perform automatic temperature compensation by sensing an external thermistor thermally coupled to the battery. The STATUS pin can be used to drive an LED indicator lamp. The device is available in a low profile (0.75mm) 7mm x 11mm 64-lead QFN package.

Applications

LT8491

  • Solar Powered Battery Chargers

  • Multiple Types of Lead-Acid Battery Charging

  • Li-Ion Battery Charger

  • Battery Equipped Industrial or Portable Military Equipment

LT8491 Device Configuration

Driver Initialization

In order to be able to use the device, you will have to provide the support for the communication protocol (I2C).

The first API to be called is lt8491_init. Make sure that it returns 0, which means that the driver was initialized correctly.

Restarting LT8491

The startup sequence is initiated when the VDD pin rises above 2.7V (typical). If the device is already powered on, the startup sequence can be re-initiated via lt8491_restart_chip API. This resets the device register values.

Enabling or Disabling Charger

Enabling or disabling charger is done using lt8491_write_enable API. This can also be read using lt8491_read_enable API. Enabling charger starts battery charging, restricts I2C write access, and commences telemetry acquisition.

Charging Status

The charging status can be read via lt8491_read_charging_status API.

1 indicates that battery charging is ongoing in one of the 4 charging stages (Stage 0 to 3).

0 indicates that the charging is not active, and the power stage has been turned off. This is indicated due to any of the following conditions:

  • The charging logic is disabled

  • The charging has been stopped due to a fault condition

  • The charging has reached the done charging stage

  • The charging logic was recently enabled but the logic hasn’t started Stage 0 charging yet

Charging Stage

The charging stage can be read via lt8491_read_charging_stage API. Values read can be any of the following:

  • ‘0’ - Stage 0

  • ‘1’ - Stage 1

  • ‘2’ - Stage 2

  • ‘3’ - Stage 3

  • ‘d’ - Done Charging

Configuring Telemetry

Specific device registers must contain valid data before the LT8491 can properly calculate telemetry for volts, amprs, power, and efficiency. The contents of these registers don’t affect any aspect of the charger’s operation. The contents of these registers are only used by the LT8491 to calculate the read-only telemetry values.

These register values can be set via setting the resistor values inside lt8491_init_param and using lt8491_configure_telemetry API.

Telemetry Acquisition

  • TBAT - battery temperature in millidegrees Celsius read via lt8491_read_tbat API

  • POUT - power delivered out of the charger in milliWatts read via lt8491_read_pout API

  • PIN - power draw from VIN supply in milliWatts read via lt8491_read_pin API

  • EFF - power conversion efficiency in 0.001 % read via lt8491_read_efficiency API

  • IOUT - current flowing out of the charger in milliamps read via lt8491_read_iout API

  • IIN - current flowing into the charger in milliamps read via lt8491_read_iin API

  • VBAT - battery voltage in millivolts read via lt8491_read_vbat API

  • VIN - input voltage from the supply in millivolts read via lt8491_read_vin API

Using Scratch Pad Register

The scratch pad register can be read and write via lt8491_read_scratch and lt8491_write_scratch APIs, respectively.

Serial Number

LT8491 has a unique serial number that consists of three (3) 16-bit numbers that can be read via lt8491_read_serial_id API.

LT8491 Driver Initialization Example

struct lt8491_device *dev;

struct no_os_uart_init_param uip = {
        .device_id = UART_DEVICE_ID,
        .baud_rate = UART_BAUDRATE,
        .size = NO_OS_UART_CS_8,
        .parity = NO_OS_UART_PAR_NO,
        .stop = NO_OS_UART_STOP_1_BIT,
        .platform_ops = UART_OPS,
        .extra = UART_EXTRA,
};

const struct no_os_i2c_init_param lt8491_i2c_ip = {
        .device_id = I2C_DEVICE_ID,
        .max_speed_hz = 100000,
        .slave_address = 0x10,
        .platform_ops = I2C_OPS,
        .extra = I2C_EXTRA,
};

struct lt8491_init_param lt8491_ip = {
        .i2c_init_param = lt8491_i2c_ip,
        .rsense1_micro_ohms = 5000,
        .rimon_out_ohms = 124000,
        .rsense2_micro_ohms = 3000,
        .rdaco_ohms = 64900,
        .rfbout1_ohms = 113000,
        .rfbout2_ohms = 10000,
        .rdaci_ohms = 7000,
        .rfbin2_ohms = 3480,
        .rfbin1_ohms = 10200,
};

ret = lt8491_init(&dev, &lt8491_ip);
if (ret)
        goto error;

LT8491 no-OS IIO support

The LT8491 IIO driver comes on top of the LT8491 driver and offers support for interfacing IIO clients through libiio.

LT8491 IIO Device Configuration

Channel Attributes

LT8491 has a total of 10 channel attributes:

  • in_temp_raw - raw battery temperature value

  • in_temp_scale - scale that has to be applied to the raw value in order to obtain the temperature value in mC

  • out_current_raw - raw current value flowing out of the charger

  • out_current_scale - scale that has to be applied to the raw value in order to obtain the current value in mA

  • in_current_supply_raw - raw current value flowing into the charger

  • in_current_supply_scale - scale that has to be applied to the raw value in order to obtain the current value in mA

  • out_voltage_raw - raw battery voltage value

  • out_voltage_scale - scale that has to be applied to the raw value in order to obtain the voltage value in mV

  • in_voltage_supply_raw - raw input voltage value

  • in_voltage_supply_scale - scale that has to be applied to the raw value in order to obtain the voltage value in mV

Debug Attributes

The device has a total of 9 debug attributes:

  • pout - Power delivered out of the charger in milliWatts

  • pin - Power draw from VIN supply in milliWatts

  • efficiency - Power conversion efficiency in 0.001 %

  • charging_stage - Charging stage

  • charging_status - Charging status

  • enable - Enable or disable charger

  • reset - Restart LT8491

  • scratch - Scratch pad register

  • serial_id - Serial number

LT8491 IIO Driver Initialization Example

int ret;

struct lt8491_iio_device *lt8491_iio_dev;
struct lt8491_iio_init_param lt8491_iio_ip = {
        .lt8491_init_param = &lt8491_ip,
};

struct iio_app_desc *app;
struct iio_app_init_param app_init_param = {0};

ret = lt8491_iio_init(&lt8491_iio_dev, &lt8491_iio_ip);
if (ret)
        goto exit;

struct iio_app_device iio_devices[] = {
        {
                .name = "lt8491",
                .dev = lt8491_iio_dev,
                .dev_descriptor = lt8491_iio_dev->iio_dev,
        },
};

app_init_param.devices = iio_devices;
app_init_param.nb_devices = NO_OS_ARRAY_SIZE(iio_devices);
app_init_param.uart_init_params = uip;

ret = iio_app_init(&app, app_init_param);
if (ret)
        goto remove_iio_lt8491;

return iio_app_run(app);