LM63 datasheet(10/28 Pages) NSC

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1.0 Functional Description (Continued)

1.3 SMBus INTERFACE

Since the LM63 operates as a slave on the SMBus the

SMBCLK line is an input and the SMBDAT line is bi-

directional. The LM63 never drives the SMBCLK line and it

does not support clock stretching. According to SMBus

specifications, the LM63 has a 7-bit slave address. All bits,

A6 through A0, are internally programmed and cannot be

changed by software or hardware.

The complete slave address is:

00110

1.4 POWER-ON RESET (POR) DEFAULT STATES

For information on the POR default states see Section 2.2

LM63 Register Map in Functional Order.

1.5 TEMPERATURE DATA FORMAT

Temperature data can only be read from the Local and

Remote Temperature registers. The High, Low and T_CRIT

setpoint registers are Read/Write.

Remote temperature data is represented by an 11-bit, two’s

complement word with a Least Significant Bit (LSB) equal to

0.125˚C. The data format is a left justified 16-bit word avail-

able in two 8-bit registers:

Temperature

Digital Output

Binary

Hex

+125˚C

0111 1101 0000 0000

7D00

+25˚C

0001 1001 0000 0000

1900

+1˚C

0000 0001 0000 0000

0100

+0.125˚C

0000 0000 0010 0000

0020

0˚C

0000 0000 0000 0000

0000

−0.125˚C

1111 1111 1110 0000

FFE0

−1˚C

1111 1111 0000 0000

FF00

−25˚C

1110 0111 0000 0000

E700

−55˚C

1100 1001 0000 0000

C900

Local Temperature data is represented by an 8-bit, two’s

complement byte with an LSB equal to 1˚C:

Temperature

Digital Output

Binary

Hex

+125˚C

0111 1101

+25˚C

0001 1001

+1˚C

0000 0001

0˚C

0000 0000

−1˚C

1111 1111

−25˚C

1110 0111

−55˚C

1100 1001

1.6 OPEN-DRAIN OUTPUTS

The SMBDAT, ALERT, and PWM outputs are open-drain

outputs and do not have internal pull-ups. A “High” level will

not be observed on these pins until pull-up current is pro-

vided by an internal source, typically through a pull-up resis-

tor. Choice of resistor value depends on several factors but,

in general, the value should be as high as possible consis-

tent with reliable operation. This will lower the power dissi-

pation of the LM63 and avoid temperature errors caused by

self-heating of the device. The maximum value of the pull-up

resistor to provide the 2.1 V high level is 88.7 k

Ω.

1.7 DIODE FAULT DETECTION

The LM63 can detect fault conditions caused by the remote

diode. If the D+ pin is detected to be shorted to V

DD, or open:

(1) the Remote Temperature High Byte (RTHB) register is

loaded with 127˚C, (2) the Remote Temperature Low Byte

(RTLB) register is loaded with 0, and (3) the OPEN bit (D2)

in the status register is set. Therefore, if the Remote T_CRIT

setpoint register (RCS): (1) is set to a value less than +127˚C

and (2) the ALERT Mask is disabled, then the ALERT output

pin will be pulled low. If the Remote High Setpoint High Byte

(RHSHB) is set to a value less than +127˚C and (2) the

ALERT Mask is disabled, then the ALERT will be pulled low.

The OPEN bit by itself will not trigger an ALERT.

If the D+ pin is shorted to either ground or D−, then the

Remote Temperature High Byte (RTHB) register is loaded

with −128˚C (1000 0000) and the OPEN bit in the ALERT

Status Register will not be set. A temperature reading of

−128˚C indicates that D+ is shorted to either ground or D-. If

the value in the Remote Low Setpoint High Byte (RLSHB)

abled, ALERT will be pulled low.

1.8 COMMUNICATING WITH THE LM63

Each data register in the LM63 falls into one of four types of

user accessibility:

Read Only

Write Only

Read/Write same address

Read/Write different address

A Write to the LM63 is comprised of an address byte and a

command byte. A write to any register requires one data

byte.

Reading the LM63 Registers can take place after the requi-

site register setup sequence takes place. See Section 2.1.1

LM63 Required Initial Fan Control Register Sequence.

The data byte has the Most Significant Bit (MSB) first. At the

end of a read, the LM63 can accept either Acknowledge or

20057009

FIGURE 5. ALERT Output as an SMBus ALERT

Temperature Response Diagram

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