Datasheet LTC2990 (Analog Devices) - 9

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OPERATION
The LTC2990 monitors voltage, current, internal and detector inhibits I2C communication below the specified remote temperatures. It can be configured through an threshold. During an undervoltage condition, the part is in I2C interface to measure many combinations of these a reset state, and the data and control registers are placed parameters. Single or repeated measurements are pos- in the default state of 00h. sible. Remote temperature measurements use a transistor Remote diode measurements are conducted using mul- as a temperature sensor, allowing the remote sensor to tiple ADC conversions and source currents to compen- be a discrete NPN (ex. MMBT3904) or an embedded PNP sate for sensor series resistance. During temperature device in a microprocessor or FPGA. The internal ADC measurements, the V2 or V4 terminal of the LTC2990 reference minimizes the number of support components is terminated with a diode. The LTC2990 is calibrated to required. yield the correct temperature for a remote diode with an The Functional Diagram displays the main components of ideality factor of 1.004. See the applications section for the device. The input signals are selected with an input compensation of sensor ideality factors other than the MUX, controlled by the control logic block. The control factory calibrated value of 1.004. logic uses the mode bits in the control register to manage The LTC2990 communicates through an I2C serial inter- the sequence and types of data acquisition. The control face. The serial interface provides access to control, sta- logic also controls the variable current sources during tus and data registers. I2C defines a 2-wire open-drain remote temperature acquisition. The order of acquisitions interface supporting multiple slave devices and masters is fixed: TINTERNAL, V1, V2, V3, V4 then VCC. The ADC on a single bus. The LTC2990 supports 100kbits/s in the performs the necessary conversion(s) and supplies the standard mode and up to 400kbit/s in fast mode. The data to the control logic for further processing in the case four physical addresses supported are listed in Table 2. of temperature measurements, or routing to the appropri- The I2C interface is used to trigger single conversions, or ate data register for voltage and current measurements. start repeated conversions by writing to a dedicated trig- Current and temperature measurements, V1 – V2 or V3 ger register. The data registers contain a destructive-read – V4, are sampled differentially by the internal ADC. The status bit (data valid), which is used in repeated mode to I2C interface supplies access to control, status and data determine if the register ’s contents have been previously registers. The ADR1 and ADR0 pins select one of four read. This bit is set when the register is updated with new possible I2C addresses (see Table 2). The undervoltage data, and cleared when read.
APPLICATIONS INFORMATION
Figure 1 is the basic LTC2990 application circuit.
Power Up
RSENSE The VCC pin must exceed the undervoltage (UV) thresh- 15mΩ 2.5V old of 2.5V to keep the LTC2990 out of power-on reset. 5V ILOAD Power-on reset will clear all of the data registers and the 0.1µF V MMBT3904 control register. CC V1 V2 2-WIRE I2C SDA V3 SCL LTC2990 INTERFACE
Temperature Measurements
ADR0 470pF ADR1 V4 GND The LTC2990 can measure internal temperature and up 2990 F01 to two external diode or transistor sensors. During tem- perature conversion, current is sourced through either the
Figure 1.
V1 or the V3 pin to forward bias the sensing diode. The Rev. F For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Pin Configuration Pin Functions Functional Diagram Timing Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts