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MAX6642ATT90-T Datasheet(PDF) 5 Page - Maxim Integrated Products |
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MAX6642ATT90-T Datasheet(HTML) 5 Page - Maxim Integrated Products |
5 / 14 page Detailed Description The MAX6642 is a temperature sensor for local and remote temperature-monitoring applications. Communication with the MAX6642 occurs through the SMBus-compatible serial interface and dedicated alert pins. ALERT asserts if the measured local or remote temperature is greater than the software-programmed ALERT limit. The MAX6642 converts temperatures to digital data either at a programmed rate of eight conversions per second or in single conversions. Temperature data is represented by 8 data bits (at addresses 00h and 01h), with the LSB equal to +1°C and the MSB equal to +128°C. Two additional bits of remote temperature data are available in the “extended” register at address 10h and 11h (Table 2) providing resolution of +0.25 °C. ADC and Multiplexer The averaging ADC integrates over a 60ms period (each channel, typ), with excellent noise rejection. The multiplexer automatically steers bias currents through the remote and local diodes. The ADC and associated circuitry measure each diode’s forward volt- age and compute the temperature based on this volt- age. Both channels are automatically converted once the conversion process has started, either in free-run- ning or single-shot mode. If one of the two channels is not used, the device still performs both measurements, and the user can ignore the results of the unused chan- nel. If the remote-diode channel is unused, connect DXP to GND rather than leaving DXP open. The conversion time per channel (remote and internal) is 125ms. If both channels are being used, then each channel is converted four times per second. If the external conversion-only option is selected, then the remote temperature is measured eight times per sec- ond. The results of the previous conversion are always available, even if the ADC is busy. Low-Power Standby Mode Standby mode reduces the supply current to less than 10µA by disabling the ADC and timing circuitry. Enter standby mode by setting the RUN bit to 1 in the config- uration byte register (Table 4). All data is retained in memory, and the SMBus interface is active and listen- ing for SMBus commands. Standby mode is not a shut- down mode. With activity on the SMBus, the device draws more supply current (see the Typical Operating Characteristics). In standby mode, the MAX6642 can be forced to perform ADC conversions through the one-shot command, regardless of the RUN bit status. If a standby command is received while a conversion is in progress, the conversion cycle is truncated, and the data from that conversion is not latched into a tempera- ture register. The previous data is not changed and remains available. Supply-current drain during the 125ms conversion peri- od is 500µA (typ). In standby mode, supply current drops to 3µA (typ). SMBus Digital Interface From a software perspective, the MAX6642 appears as a set of byte-wide registers that contain temperature data, alarm threshold values, and control bits. A stan- dard SMBus-compatible 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. The MAX6642 employs four standard SMBus protocols: Write Byte, Read Byte, Send Byte, and Receive Byte. (Figures 1, 2, and 3). The shorter Receive Byte protocol allows quicker transfers, provided that the correct data ±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm _______________________________________________________________________________________ 5 Pin Description PIN NAME FUNCTION 1VCC Supply Voltage Input, +3V to +5.5V. Bypass VCC to GND with a 0.1µF capacitor. A 47 Ω series resistor is recommended but not required for additional noise filtering. 2 GND Ground 3 DXP Combined Remote-Diode Current Source and ADC Input for Remote-Diode Channel. Place a 2200pF capacitor between DXP and GND for noise filtering. 4 SCLK SMBus Serial-Clock Input. May be pulled up to +5.5V regardless of VCC. 5 SDA SMBus Serial-Data Input/Output, Open Drain. May be pulled up to +5.5V regardless of VCC. 6 ALERT SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds user-set limits. See the ALERT Interrupts section. —EP Exposed Pad. Internally connected to GND. Connect to a PCB ground pad for optimal performance. Not intended as an electrical connection point. |
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