MAX1989MUE+【PDF 6/17 页】IC TEMP SENSOR REMOTE 16TSSOP

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Multichannel Remote/Local

Temperature Sensors

6 _______________________________________________________________________________________

_______________Detailed Description

The MAX1668/MAX1805/MAX1989 are temperature

sensors designed to work in conjunction with an exter-

nal microcontroller (礐) or other intelligence in thermo-

static, process-control, or monitoring applications. The

礐 is typically a power-management or keyboard con-

troller, generating SMBus serial commands by bit-

banging general-purpose input-output (GPIO) pins or

through a dedicated SMBus interface block.

These devices are essentially 8-bit serial analog-to-digi-

tal converters (ADCs) with sophisticated front ends.

However, the MAX1668/MAX1805/MAX1989 also contain

a switched current source, a multiplexer, an ADC, an

SMBus interface, and associated control logic (Figure 1).

In the MAX1668 and MAX1989, temperature data from

the ADC is loaded into five data registers, where it is

automatically compared with data previously stored in

10 over/undertemperature alarm registers. In the

MAX1805, temperature data from the ADC is loaded into

three data registers, where it is automatically compared

with data previously stored in six over/undertemperature

alarm registers.

ADC and Multiplexer

The ADC is an averaging type that integrates over a

64ms 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.

Each channel is automatically converted once the con-

version process has started. If any one of the channels

is not used, the device still performs measurements on

these channels, and the user can ignore the results of

the unused channel. If any remote-diode channel is

unused, connect DXP_ to DXN_ rather than leaving the

pins open.

The DXN_ input is biased at 0.65V above ground by an

internal diode to set up the A/D inputs for a differential

measurement. The worst-case DXP_ to DXN_ differential

input voltage range is 0.25V to 0.95V.

Excess resistance in series with the remote diode caus-

es about +0.5癈 error per ohm. Likewise, 200礦 of offset

voltage forced on DXP_ to DXN_ causes about 1癈 error.

MAX1668/

MAX1989

FUNCTION

1, 3, 5, 7

DXP_

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

leave DXP floating; connect DXP to DXN if no remote diode is used. Place a 2200pF

capacitor between DXP and DXN for noise filtering.

ALERT

SMBus Alert (Interrupt) Output, Open Drain

ADD0

SMBus Slave Address Select Pin

ADD1

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

Excess capacitance (>50pF) at the address pins when floating can cause address-

recognition problems.

STBY

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

standby mode. Low = standby mode, high = operate mode.

SMBCLK

SMBus Serial-Clock Input

SMBDATA

SMBus Serial-Data Input/Output, Open Drain

1, 3

Pin Description

NAME

MAX1805

2, 4, 6, 8

DXN_

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

age above ground.

2, 4

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

resistor is recommended but not required for additional noise filtering.

GND

Ground

N.C.

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

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