+145°C Precision SMBus-Compatible Remote/

Local Sensors with Overtemperature Alarms

10

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 appli-

cations. The conversion rate byte’s POR state is 07h or

4Hz. The MAX6646/MAX6647/MAX6649 look only at the 3

LSBs of this register, so the upper 5 bits are “don’t care”

bits, which should be set to zero. The conversion rate tol-

erance is ±25% at any rate setting.

Valid A/D conversion results for both channels are avail-

able two total conversion times (250ms nominal, 312ms

maximum) after initiating a conversion, whether conver-

sion is initiated through the RUN bit, one-shot com-

mand, or initial power-up. Changing the conversion rate

can also affect the delay until new results are available.

REGISTER

ADDRESS

POR STATE

FUNCTION

RLTS

00h

0000 0000

0°C

Read local (internal) temperature

RRTE

01h

0000 0000

0°C

Read remote (external) temperature

RSL

02h

N/A

—

Read status byte

RCL

03h

0000 0000

—

Read configuration byte

RCRA

04h

0000 0111

—

Read conversion rate byte

RLHN

05h

0101 0101

+85°C

Read local (internal) ALERT high limit

RLLI

06h

0000 0000

0°C

Read local (internal) ALERT low limit

0101 1111

+95°C

Read remote (external) ALERT high limit (MAX6646/MAX6647)

RRHI

07h

0101 0101

+85°C

Read remote (external) ALERT high limit (MAX6649)

RRLS

08h

0000 0000

0°C

Read remote (external) ALERT low limit

WCA

09h

N/A

—

Write configuration byte

WCRW

0Ah

N/A

—

Write conversion rate byte

WLHO

0Bh

N/A

—

Write local (internal) ALERT high limit

WLLM

0Ch

N/A

—

Write local (internal) ALERT low limit

WRHA

0Dh

N/A

—

Write remote (external) ALERT high limit

WRLN

0Eh

N/A

—

Write remote (external) ALERT low limit

OSHT

0Fh

N/A

—

One-shot

REET

10h

0000 0000

0°C

Read remote (external) extended temperature

RIET

11h

0000 0000

0°C

Read local (internal) extended temperature

0111 1101

+125°C

Read/write remote (external) OVERT limit (MAX6646/MAX6647)

RWOE

19h

0101 0101

+85°C

Read/write remote (external) OVERT limit (MAX6649)

RWOI

20h

0101 0101

+85°C

Read/write local (internal) OVERT limit

HYS

21h

0000 1010

10°C

Overtemperature hysteresis

QUEUE

22h

1000 0110

—

Fault queue

—

FEh

0100 1101

—

Read manufacture ID

—

FFh

0101 1001

—

Read revision ID

Table 5. Command-Byte Bit Assignments

BIT

NAME

POR STATE

FUNCTION

7 (MSB)

MASK

0

Masks ALERT interrupts when set to 1.

6

RUN

0

Standby mode control bit; if set to 1, standby mode is initiated.

5 to 0

RFU

0

Reserved.

Table 6. Configuration-Byte Bit Assignments (03h)