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MAX6642
(Rev.:2003)

±1°C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm

Maxim Integrated 

±1°C, SMBus-Compatible Remote/Local

Temperature Sensor with Overtemperature Alarm

When a conversion is complete, the main temperature

register and the extended temperature register are

updated.

Alarm Threshold Registers

Two registers store ALERT threshold values—one each

for the local and remote channels. If either measured

temperature equals or exceeds the corresponding

ALERT threshold value, the ALERT interrupt asserts

unless the ALERT bit is masked.

The power-on-reset (POR) state of the local ALERT

THIGH register is +70°C (0100 0110). The POR state of

the remote ALERT THIGH register is +120°C (0111 1000).

Diode Fault Detection

A continuity fault detector at DXP detects an open cir-

cuit on DXP, or a DXP short to VCC or GND. If an open

or short circuit exists, the external temperature register

is loaded with 1111 1111 and status bit 2 (OPEN) of the

status byte is set to 1. Immediately after POR, the sta-

tus register indicates that no fault is present. If a fault is

present upon power-up, the fault is not indicated until

the end of the first conversion. Diode faults do not set

the ALERT output.

ALERT Interrupts

The ALERT interrupt occurs when the internal or external

temperature reading exceeds a high temperature limit

(user programmed). The ALERT interrupt output signal is

latched and can be cleared only by reading the status

register after the fault condition no longer exists or by

successfully responding to the alert response address. If

the ALERT is cleared by responding to the alert

response address and the temperature fault condition

still exists, ALERT is reasserted after the next tempera-

ture-monitoring cycle. To clear ALERT while the tempera-

Table 1. Main Temperature Register

(High Byte) Data Format

TEMP (°C)

130.00

127.00

126.00

25

0.00

<0.00

Diode fault (short or open)

DIGITAL OUTPUT

1 000 0010

0 111 1111

0 111 1110

0 001 1001

0 000 0000

0 000 0000

1 111 1111

Table 2. Extended Resolution

Temperature Register (Low Byte) Data

Format

FRACTIONAL TEMP (°C)

0.000

0.250

0.500

0.750

DIGITAL OUTPUT

00XX XXXX

01XX XXXX

10XX XXXX

11XX XXXX

ture is above the trip threshold, write a new high limit that

is higher than the current temperature. The ALERT out-

put is open drain, allowing multiple devices to share a

common interrupt line.

Alert Response Address

The SMBus alert response interrupt pointer provides

quick fault identification for simple slave devices like

temperature sensors. Upon receiving an ALERT inter-

rupt signal, the host master can broadcast a Receive

Byte transmission to the alert response slave address

A

B

C

D

EF

G

tLOW tHIGH

SMBCLK

H

I JK

LM

SMBDATA

tSU:STA tHD:STA

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

E = SLAVE PULLS SMBDATA LINE LOW

tSU:DAT

tHD:DAT

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO MASTER

H = LSB OF DATA CLOCKED INTO MASTER

I = MASTER PULLS DATA LINE LOW

Figure 3. SMBus Read Timing Diagram

tSU:STO tBUF

J = ACKNOWLEDGE CLOCKED INTO SLAVE

K = ACKNOWLEDGE CLOCK PULSE

L = STOP CONDITION

M = NEW START CONDITION

_______________________________________________________________________________________ 7

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