MAX6647 Просмотр технического описания (PDF) - Maxim Integrated

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MAX6647

+145°C Precision SMBus-Compatible Remote/ Local Sensors with Overtemperature Alarms

Maxim Integrated 

+145°C Precision SMBus-Compatible Remote/

Local Sensors with Overtemperature Alarms

Table 3. Fault Queue Register Bit Definition

(22h)

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

1

Fault queue-length control

bit (see Table 4).

1

FQ0

1

Fault queue-length control

bit (see Table 4).

0

RFU

0

Reserved. Always write

zero to this bit.

The alert response can activate several different slave

devices simultaneously, similar to the I2C 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 acknowl-

edge 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 com-

pletion of the read alert response protocol 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 trig-

ger a system shutdown to prevent component 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

MAX6646/MAX6647/MAX6649. 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 MAX6646/MAX6647/MAX6649 incorporate collision

avoidance so that completely asynchronous operation is

allowed between SMBus operations and temperature

conversions.

Table 4. Fault Queue Length Bit Definition

FQ1 FQ0

0

0

0

1

1

1

1

0

FAULT QUEUE LENGTH (SAMPLES)

1

2

3

1

One-Shot

The one-shot command immediately forces a new con-

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

received while the MAX6646/MAX6647/MAX6649 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 com-

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

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

between conversions, a new conversion begins, the con-

version rate timer is reset, and the next automatic conver-

sion takes place after a full delay elapses.

Configuration Byte Functions

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

register with several functions. Bit 7 is used to mask (dis-

able) interrupts. Bit 6 puts the MAX6646/MAX6647/

MAX6649 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 conversion is complete

and if the fault condition 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 THIGH and TLOW 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 (especially when

converting at the fastest rate). In these circumstances, 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.

9

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