LTC2991.h File Reference

The LTC2991 is used to monitor system temperatures, voltages and currents.
Through the I2C serial interface, the eight monitors can individually measure
supply voltages and can be paired for differential measurements of current sense
resistors or temperature sensing transistors. Additional measurements include
internal temperature and internal VCC. The internal 10ppm reference minimizes
the number of supporting components and area required. Selectable address and
configurable functionality give the LTC2991 flexibility to be incorporated in
various systems needing temperature, voltage or current data. The LTC2991 fits
well in systems needing submillivolt voltage resolution, 1% current measurement
and 1 degree Celsius temperature accuracy or any combination of the three.

I2C DATA FORMAT (MSB FIRST);

Data Out:
Byte #1                                     Byte #2                    Byte #3

START  SA6 SA5 SA4 SA3 SA2 SA1 SA0 W SACK   X X X X C3 C2 C1 C0 SACK   D7 D6 D5 D4 D3 D2 D1 D0 SACK STOP

Data In:
Byte #1                                     Byte #2                                  Byte #3

START  SA6 SA5 SA4 SA3 SA2 SA1 SA0 W SACK   X X X X C3 C2 C1 C0 SACK   REPEAT START  SA6 SA5 SA4 SA3 SA2 SA1 SA0 R SACK

Byte #4                              Byte #5
MSB                                  LSB
D15 D14 D13 D12 D11 D10 D9 D8 MACK   D7 D6 D5 D4 D3 D2 D1 D0 MNACK STOP

START        : I2C Start
REPEAT Start : I2C Repeat Start
STOP         : I2C Stop
SACK         : I2C Slave Generated Acknowledge (Active Low)
MACK         : I2C Master Generated Acknowledge (Active Low)
MNACK        : I2C Master Generated Not Acknowledge
SAx  : I2C Address
W    : I2C Write (0)
R    : I2C Read  (1)
Cx   : Command Code
Dx   : Data Bits
X    : Don't care


Example Code:

Read single-ended voltage from V1.

    // Enable Single-Ended Mode
    ack |= LTC2991_register_set_clear_bits(LTC2991_I2C_ADDRESS, LTC2991_CONTROL_V1234_REG, 0x00, LTC2991_V1_V2_DIFFERENTIAL_ENABLE | LTC2991_V1_V2_TEMP_ENABLE);

    // Flush one ADC reading in case it is stale.  Then, take a new fresh reading.
    ack |= LTC2991_adc_read_new_data(LTC2991_I2C_ADDRESS, LTC2991_V1_MSB_REG, &code, &data_valid, LTC2991_TIMEOUT);

    voltage = LTC2991_code_to_single_ended_voltage(code, LTC2991_SINGLE_ENDED_lsb); // Converts code to voltage from single-ended lsb

Read current from V3-V4.

    resistor = 1; // R_sense across V3-V4 in ohms

    // Enable Differential Mode
    ack |= LTC2991_register_set_clear_bits(LTC2991_I2C_ADDRESS, LTC2991_CONTROL_V1234_REG, LTC2991_V3_V4_DIFFERENTIAL_ENABLE, LTC2991_V3_V4_TEMP_ENABLE);

    // Flush one ADC reading in case it is stale.  Then, take a new fresh reading.
    ack |= LTC2991_adc_read_new_data(LTC2991_I2C_ADDRESS, LTC2991_V4_MSB_REG, &code, &data_valid, LTC2991_TIMEOUT);

    voltage = LTC2991_code_to_differential_voltage(code, LTC2991_DIFFERENTIAL_lsb); // Converts code to voltage from differential lsb
    current = voltage / resistor; // Calculates current

Read temperature from diode connected to V7-V8.

    // Enable temperature mode.
    ack |= LTC2991_register_set_clear_bits(LTC2991_I2C_ADDRESS, LTC2991_CONTROL_V5678_REG, LTC2991_V7_V8_TEMP_ENABLE, 0x00);

    // Flush one ADC reading in case it is stale.  Then, take a new fresh reading.
    ack |= LTC2991_adc_read_new_data(LTC2991_I2C_ADDRESS, LTC2991_V7_MSB_REG, &adc_code, &data_valid, LTC2991_TIMEOUT);

    // Converts code to temperature from adc code and temperature lsb
    temperature = LTC2991_temperature(adc_code, LTC2991_TEMPERATURE_lsb);