Datasheet MAX31889 (Maxim) - 8

link to page 8 link to page 9 MAX31889 ±0.25°C Accurate I2C Temperature Sensor
Detailed Description
The MAX31889 temperature sensor provides 16-bit Celsius temperature measurements with ±0.25°C accuracy over a -20°C to +105°C temperature range and ±0.65°C accuracy over a -40°C to +125°C temperature range. A host can communicate with the sensor over an I2C/SMBus-compatible 2-wire interface with serial data (SDA) and serial clock (SCL) lines to read the FIFO, which contains up to 32, 2-byte temperature readings. In addition to the FIFO, the interface provides access to the 2-byte high alarm trigger and 2-byte low alarm trigger registers (AH and AL) and a temperature sensor setup register. The Alarm High, Alarm Low, and Setup registers are volatile, so they don’t retain data when the device is powered down. The MAX31889 offers two programmable GPIO pins. The default state of the GPIO pins at power-up determines the 2 LSBs in the I2C address of the device. GPIO1 allows for an optional external convert temperature trigger while GPIO0 can be configured as an interrupt for selectable status bits.
Operation Measuring Temperature
The sensor powers up in a low-power standby state. To initiate a temperature measurement, the master must write a '1' to the CONVERT_T bit in the TEMP_SENSOR_SETUP [0x14] register. At temperature range of -40°C to 0°C, do not sample at more than 1Hz, as the total time for a sample to be ready after sending a conversion command can be up to 1s. At temperature range of 0°C to 125°C, do not sample at more than 20Hz, as the total time for a sample to be ready after sending a conversion command can be up to 50ms. Following the conversion, which takes 15ms (typ), the resulting temperature data is stored in the FIFO, and the device returns to the standby state. CONVERT_T automatically clears to '0'. The output temperature data is calibrated in degrees Celsius. The temperature data is stored as a left-justified, 16-bit sign-extended two’s complement number in the FIFO Data register (see Figure 1). The data is two's complement where the MSB indicates the sign of the temperature, with an MSB of 1 indicating a negative temperature and an MSB of 0 indicating a positive temperature. To calculate the temperature from the measurement data, convert the two's complement value to the decimal value and use the following equation for 16-bit resolution. T = Decimal Value x 0.005 For example, if the result is 0x1CE8, convert to decimal to get 7400, then T = 7400 x 0.005, or 37°C. Table 1 gives examples of digital output data and the corresponding temperature reading. TEMPERATURE DATA REGISTER FORMAT Bit15 Bit14 Bit13 Bit12 Bit11 Bit10 Bit9 Bit8 MSB T15 T14 T13 T12 T11 T10 T9 T8 Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 LSB T7 T6 T5 T4 T3 T2 T1 T0 Figure 1. Temperature Data Register Format 19-100693 www.maximintegrated.com Maxim Integrated | 8 Document Outline General Description Applications Benefits and Features Simplified Block Diagram Absolute Maximum Ratings Package Information μDFN Electrical Characteristics Electrical Characteristics (continued) Typical Operating Characteristics Typical Operating Characteristics (continued) Pin Configuration μDFN Pin Description Functional Diagrams Detailed Description Operation Measuring Temperature Alarm Signaling GPIO I2C I2C Slave Address I2C/SMBus Compatible Serial Interface Detailed I2C Timing Diagram Bit Transfer START and STOP Conditions Early STOP Conditions Acknowledge Bit I2C Write Data Format I2C Read Data Format FIFO Description Register Map Register Map Register Details STATUS (0x0) INTERRUPT ENABLE (0x1) FIFO WRITE POINTER (0x04) FIFO READ POINTER (0x05) FIFO OVERFLOW COUNTER (0x06) FIFO DATA COUNTER (0x07) FIFO DATA (0x08) FIFO CONFIGURATION 1 (0x09) FIFO CONFIGURATION 2 (0x0A) SYSTEM CONTROL (0x0C) ALARM HIGH MSB (0x10) ALARM HIGH LSB (0x11) ALARM LOW MSB (0x12) ALARM LOW LSB (0x13) TEMP SENSOR SETUP (0x14) GPIO SETUP (0x20) GPIO CONTROL (0x21) ROM ID 1 (0x31) ROM ID 2 (0x32) ROM ID 3 (0x33) ROM ID 4 (0x34) ROM ID 5 (0x35) ROM ID 6 (0x36) PART IDENTIFIER (0xFF) Applications Information Measurement Considerations Typical Application Circuit Ordering Information Revision History