Datasheet MAX1618 (Maxim) - 6

Remote Temperature Sensor with SMBus Serial Interface Pin Description PIN NAME FUNCTION
SMBus Slave Address Select Input. (See Table 6.) ADD0 and ADD1 are sampled upon power-up. Excess 1 ADD0 capacitance (>50pF) at the address pins when floating may cause address-recognition problems. SMBus Slave Address Select Input. (See Table 6.) ADD0 and ADD1 are sampled upon power-up. Excess 2 ADD1
MAX1618
capacitance (>50pF) at the address pins when floating may cause address-recognition problems. 3 GND Ground Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode voltage above 4 DXN ground. Combined Current Source and A/D Positive Input. Do not leave DXP floating. Place a 2200pF capacitor 5 DXP between DXP and DXN for noise filtering. 6 VCC Supply Voltage Input. Bypass to GND with a 0.1µF capacitor. Hardware-Standby Input. Temperature and comparison threshold data are retained in standby mode. 7 STBY Low = standby mode. High = operating mode. 8 SMBCLK SMBus Serial-Clock Input 9 SMBDATA SMBus Serial-Data Input/Output. Open drain. 10 ALERT SMBus Alert (Interrupt) Output. Open drain.
Detailed Description
currents through the remote diode, measures the for- ward voltage, and computes the temperature. The MAX1618 is a temperature sensor designed to work in conjunction with an external microcontroller The DXN input is biased at 0.65V above ground by an (µC) or other intelligence in thermostatic, process-con- internal diode to set up the analog-to-digital (A/D) trol, or monitoring applications. The µC is typically a inputs for a differential measurement. The worst-case power-management or keyboard controller, generating DXP-DXN differential input voltage range is 0.25V to SMBus serial commands by “bit-banging” general-pur- 0.95V. pose input-output (GPIO) pins or through a dedicated Excess resistance in series with the remote diode SMBus interface block. causes about +1/2°C error/Ω. A 200µV offset voltage at Essentially an 8-bit serial analog-to-digital converter DXP-DXN causes about +1°C error. (ADC) with a sophisticated front end, the MAX1618
A/D Conversion Sequence
contains a switched-current source, a multiplexer, an If a Start command is written (or generated automatical- ADC, an SMBus interface, and the associated control ly in the free-running autoconvert mode), the result of logic (Figure 1). Temperature data from the ADC is the measurement is available after the end of conver- loaded into a data register, where it is automatically sion. A BUSY status bit in the status byte shows that the compared with data previously stored in over/under- device is performing a new conversion. The result of the temperature alarm threshold registers. The alarm previous conversion is always available even when the threshold registers can be set for hysteretic fan control. ADC is busy.
ADC and Multiplexer
The averaging ADC integrates over a 30ms period (typ) with excellent noise rejection. The ADC converts at a rate of 16Hz. The multiplexer automatically steers bias
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