6

Remote/Local Temperature Sensor

with SMBus Serial Interface

MAX1617A

Maxim Integrated

Pin Description

General Description

The MAX1617A is a temperature sensor designed to

work in conjunction with an external microcontroller

(µC) or other intelligence in thermostatic, process-con-

trol, or monitoring applications. The µC is typically a

power-management or keyboard controller, generating

SMBus serial commands by “bit-banging” general-pur-

pose input/output (GPIO) pins or via a dedicated

SMBus interface block.

Essentially an 8-bit serial analog-to-digital converter

(ADC) with a sophisticated front end, the MAX1617A

contains a switched current source, a multiplexer, an

ADC, an SMBus interface, and associated control logic

(Figure 1). Temperature data from the ADC is loaded

into two data registers, where it is automatically com-

pared with data previously stored in four over/under-

temperature alarm registers.

ADC and Multiplexer

The ADC is an averaging type that integrates over a

60ms period (each channel, typical) with excellent

noise rejection.

The multiplexer automatically steers bias currents

through the remote and local diodes, measures their

forward voltages, and computes their temperatures.

Both channels are automatically converted once the

conversion process has started, either in free-running

or single-shot mode. If one of the two channels is not

used, the device still performs both measurements, and

the user can simply ignore the results of the unused

channel. If the remote diode channel is unused, tie DXP

to DXN rather than leaving the pins open.

The DXN input is biased at 0.65V(typ) above ground by

an internal diode to set up the analog-to-digital (A/D)

inputs for a differential measurement. The typical

DXP–DXN differential input voltage range is 0.25V to

0.95V. To ensure proper operation over full temperature

SMBus Serial-Data Input/Output, Open Drain

SMBDATA

12

SMBus Serial-Clock Input

SMBCLK

14

Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode.

Low = standby mode, high = operate mode.

STBY

15

SMBus Address Select Pin (Table 8). ADD0 and ADD1 are sampled upon power-up. Excess capacitance

(>50pF) at the address pins when unconnected may cause address-recognition problems.

ADD1

6

Ground

GND

7, 8

SMBus Slave Address Select Pin

ADD0

10

SMBus Alert (interrupt) Output, Open Drain

ALERT

11

Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode voltage above

ground.

DXN

4

Combined Current Source and A/D Positive Input for Remote-Diode Channel. Do not leave DXP uncon-

nected; tie DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for

noise filtering.

DXP

3

PIN

Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1µF capacitor. A 200

Ω series resistor is recom-

mended but not required for additional noise filtering.

2

No Connection. Not internally connected. May be used for PC board trace routing.

N.C.

1, 5, 9,

13, 16

FUNCTION

NAME