MAX6692YMUA+T Datasheet MAX6648MUA+, MAX6692YMUA+, MAX6692MUA+ | P7-P9

MAX6648/MAX6692

Precision SMBus-Compatible Remote/Local

Temperature Sensors with Overtemperature Alarms

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2) If the MAX6648/MAX6692 are in run mode, read the

status byte. If the BUSY bit indicates that a conversion

is in progress, wait until the conversion is complete

(BUSY bit set to zero) before reading the temperature

data. Following a conversion completion, immediately

read the contents of the temperature data registers. If

no conversion is in progress, the data can be read

within a few microseconds, which is a sufficiently short

period of time to ensure that a new conversion cannot

be completed until after the data has been read.

SMBCLK

AB CD

FG H

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 2. SMBus Write Timing Diagram

Write Byte Format

Read Byte Format

Send Byte Format

Receive Byte Format

Slave Address: equiva-

lent to chip-select line of

a 3-wire interface

Command Byte: selects which

Data Byte: data goes into the register

set by the command byte (to set

thresholds, configuration masks, and

sampling rate)

Slave Address: equiva-

lent to chip-select line

Command Byte: selects

which register you are

reading from

Slave Address: repeated

due to change in data-

flow direction

Data Byte: reads from

the register set by the

command byte

Command Byte: sends com-

mand with no data, usually

used for one-shot command

Data Byte: reads data from

the register commanded

by the last Read Byte or

Write Byte transmission;

also used for SMBus Alert

Response return address

S = Start condition Shaded = Slave transmission

P = Stop condition /// = Not acknowledged

Figure 1. SMBus Protocols

S ADDRESS RD ACK DATA /// P

7 bits 8 bits

WRS ACK COMMAND ACK P

8 bits

ADDRESS

7 bits

ACKDATA

8 bits

ACKCOMMAND

8 bits

ACKWRADDRESS

7 bits

S ADDRESS WR ACK COMMAND ACK S ADDRESS

7 bits8 bits7 bits

RD ACK DATA

8 bits

/// P

MAX6648/MAX6692

Precision SMBus-Compatible Remote/Local

Temperature Sensors with Overtemperature Alarms

______________________________________________________________________________________________________________________________________________________________________________

SMBCLK

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

AB CD

HIJ

SMBDATA

SU:STA

HD:STA

LOW

HIGH

SU:DAT

SU:STO

BUF

LMK

E = SLAVE PULLS SMBDATA LINE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO SLAVE

H = LSB OF DATA CLOCKED INTO SLAVE

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

Alarm Threshold Registers

Four registers store ALERT threshold values—one high-

temperature (T

HIGH

) and one low-temperature (T

LOW

)

either measured temperature equals or exceeds the

corresponding ALERT threshold value, the ALERT inter-

rupt asserts.

The power-on-reset (POR) state of both ALERT T

HIGH

registers is full scale (0101 0101, or +85°C). The POR

state of both T

LOW

registers is 0000 0000, or 0°C.

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 POR state of the

OVERT threshold is 0110 1110 or +110°C for the

MAX6648, and 0101 0101 or +85°C for the MAX6692.

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 1000 0000.

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

status byte, it is set to 1 and the ALERT condition 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 exter-

nal temperature reading exceeds a high- or low-tem-

perature limit (user programmed) or 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 only if the

fault condition no longer exists. Asserting ALERT does

not halt automatic conversion. The ALERT output pin is

open drain, allowing multiple devices to share a com-

mon interrupt line.

The MAX6648/MAX6692 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 2 and 3 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.

The alert response can activate several different slave

devices simultaneously, similar to the I

C general call. If

more than one slave attempts to respond, bus arbitration

rules apply, and the device with the lower address

code wins. The losing device does not generate an

MAX6648/MAX6692

Precision SMBus-Compatible Remote/Local

Temperature Sensors with Overtemperature Alarms

______________________________________________________________________________________________________________________________________________________________________________

acknowledge and continues to hold the ALERT line low

until cleared. (The conditions for clearing an ALERT

vary, depending on the type of slave device).

Successful completion of the read alert response proto-

col clears the interrupt latch, provided the condition

that caused the alert no longer exists.

OVERT

Overtemperature Alarm/Warning

Outputs

OVERT asserts when the temperature rises to a value

stored in one of the OVERT limit registers (19h, 20h). It

deasserts when the temperature drops below the

stored limit, minus hysteresis. OVERT can be used to

activate a cooling fan, send a warning, invoke clock

throttling, or trigger a system shutdown to prevent com-

ponent damage.

Command Byte Functions

The 8-bit command byte register (Table 5) is the master

index that points to the various other registers within the

MAX6648/MAX6692. The register’s POR state is 0000

0000, so a receive byte transmission (a protocol that

lacks the command byte) that occurs immediately after

POR, returns the current local temperature data.

The MAX6648/MAX6692 incorporate collision avoid-

ance so that completely asynchronous operation is

allowed between SMBus operations and temperature

conversions.

One-Shot

The one-shot command immediately forces a new con-

version cycle to begin. If the one-shot command is

received while the MAX6648/MAX6692 are in standby

mode (RUN bit = 1), a new conversion begins, after

which the device returns to standby mode. If a one-shot

conversion is in progress when a one-shot command is

received, the command is ignored. If a one-shot com-

mand is received in autonomous mode (RUN bit = 0)

between conversions, a new conversion begins, the

conversion rate timer is reset, and the next automatic

conversion takes place after a full delay elapses.

Configuration Byte Functions

The configuration byte register (Table 6) is a read-write

able) interrupts. Bit 6 puts the MAX6648/MAX6692 into

standby mode (STOP) or autonomous (RUN) mode.

Status Byte Functions

The status byte register (Table 7) indicates which (if

any) temperature thresholds have been exceeded. This

byte also indicates whether the ADC is converting and

whether there is an open-circuit fault detected in the

external sense junction. After POR, the normal state of

all flag bits is zero, assuming no alarm conditions are

present. The status byte is cleared by any successful

read of the status byte, after a conversion is complete

and the fault no longer exists. Note that the ALERT

interrupt latch is not automatically cleared when the

status flag bit indicating the ALERT is cleared. The fault

condition must be eliminated before the ALERT output

can be cleared.

When autoconverting, if the T

HIGH

and T

LOW

limits are

close together, it is possible for both high-temp and

low-temp status bits to be set, depending on the

amount of time between status read operations (espe-

cially when converting at the fastest rate). In these cir-

cumstances, it is best not to rely on the status bits to

indicate reversals in long-term temperature changes.

Instead use a current temperature reading to establish

the trend direction.

Conversion Rate Byte

The conversion rate register (Table 8) programs the

time interval between conversions in free-running

autonomous mode (RUN = 0). This variable rate control

can be used to reduce the supply current in portable-

equipment applications. The conversion rate byte’s

POR state is 07h or 4Hz. The MAX6648/MAX6692 look

BIT NAME

POR

STATE

FUNCTION

7 RFU 1

Reserved. Always write 1 to

this bit.

6 to 3 RFU 0

Reserved. Always write

zero to this bit.

2 FQ1 0

Fault queue-length control

bit (see Table 4).

1 FQ0 0

Fault queue-length control

bit (see Table 4).

0 RFU 0

Reserved. Always write

zero to this bit.

Table 3. Fault Queue Register Bit Definition

(22h)

FQ1 FQ0 FAULT QUEUE LENGTH (SAMPLES)

00 1

01 2

11 3

10 —

Table 4. Fault Queue Length Bit Definition

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P16

MAX6692YMUA+T

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Board Mount Temperature Sensors Remote/Local Temperature Sensor

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