MAX6649MUA/V+【PDF 8/16 页】IC SENSOR REMOTE SMBUS 8UMAX

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+145癈 Precision SMBus-Compatible Remote/

Local Sensors with Overtemperature Alarms

Alarm Threshold Registers

Four registers store ALERT threshold valuesone high-

temperature (T

HIGH

) and one low-temperature (T

LOW

)

measured temperature equals or exceeds the corre-

sponding ALERT threshold value, the ALERT interrupt

asserts.

The MAX6646/MAX6647 local (internal) ALERT T

HIGH

remote (external) ALERT T

HIGH

0101 1111, or +95癈.The MAX6649 POR state of both

ALERT T

HIGH

registers is 0101 0101, or +85癈. The POR

state of the local and remote T

LOW

registers for all

devices is 0000 0000, or 0癈.

Two additional registers store remote and local alarm

threshold data corresponding to the OVERT output. The

values stored in these registers are high-temperature

thresholds. If either of the measured temperatures equals

or exceeds the corresponding alarm threshold value, an

OVERT output asserts. The MAX6646/MAX6647 local

(internal) OVERT register POR state is 0101 0101, or

+85癈, while the remote (external) OVERT register POR

state is 0111 1101, or +125癈. The MAX6649 POR state

of both OVERT registers is 0101 0101, or +85癈.

Diode Fault Alarm

A continuity fault detector at DXP detects an open cir-

cuit between DXP and DXN, or a DXP short to V

GND, or DXN. If an open or short circuit exists, the

external temperature register is loaded with 1111 1111.

If the fault is an open-circuit fault bit 2 (OPEN), the sta-

tus byte is set to 1. In the MAX6649, ALERT is activated

at the end of the conversion. Immediately after POR,

the status 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.

ALERT Interrupts

The ALERT interrupt occurs when the internal or external

temperature reading exceeds a high- or low-temperature

limit (programmed) or in the MAX6649, when the remote

diode is disconnected (for continuity fault detection). The

ALERT interrupt output signal is latched and can be

cleared only by either reading the status register or by

successfully responding to an alert response address. In

both cases, the alert is cleared if the fault condition no

longer exists. Asserting ALERT does not halt automatic

conversion. The ALERT output is open drain, allowing

multiple devices to share a common interrupt line.

The MAX6646/MAX6647/MAX6649 respond to the

SMBus alert response address, an interrupt pointer

return-address feature (see the Alert Response

Address section). Prior to taking corrective action,

always check to ensure that an interrupt is valid by

reading the current temperature.

Fault Queue Register

In some systems, it may be desirable to ignore a single

temperature measurement that falls outside the ALERT

limits. Bits 1 and 2 of the fault queue register (address

22h) determine the number of consecutive temperature

faults necessary to set ALERT (see Tables 3 and 4).

Alert Response Address

The SMBus alert response interrupt pointer provides

quick fault identification for simple slave devices that

lack the complex, expensive logic needed to be a bus

master. Upon receiving an ALERT interrupt signal, the

host master can broadcast a receive byte transmission

to the alert response slave address (0001 100).

Following such a broadcast, any slave device that gen-

erated an interrupt attempts to identify itself by putting

its own address on the bus.

SMBCLK

E F

I J K

SMBDATA

SU:STA

HD:STA

LOW

HIGH

SU:DAT

HD:DAT

SU:STO

BUF

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

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

J = ACKNOWLEDGE CLOCKED INTO SLAVE

K = ACKNOWLEDGE CLOCK PULSE

L = STOP CONDITION

M = NEW START CONDITION

Figure 3. SMBus Read Timing Diagram

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