LM89

SNIS128D – AUGUST 2002 – REVISED JUNE 2014

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Version

A6

A5

A4

A3

A2

A1

A0

LM89CIM, LM89CIMM

1

0

0

1

1

0

0

LM89-1CIMM, LM89-

1

0

0

1

1

0

1

1DIMM

9.3.5 Temperature Data Format

Temperature data can only be read from the Local and Remote Temperature registers; the setpoint registers

(T_CRIT, LOW, HIGH) are read/write.

Remote temperature data is represented by an 11-bit, two's complement word with an LSB (Least Significant Bit)

equal to 0.125°C. The data format is a left justified 16-bit word available in two 8-bit registers:

Temperature

Digital Output

Binary

Hex

+125°C

0111 1101 0000 0000

7D00h

+25°C

0001 1001 0000 0000

1900h

+1°C

0000 0001 0000 0000

0100h

+0.125°C

0000 0000 0010 0000

0020h

0°C

0000 0000 0000 0000

0000h

−0.125°C

1111 1111 1110 0000

FFE0h

−1°C

1111 1111 0000 0000

FF00h

−25°C

1110 0111 0000 0000

E700h

−55°C

1100 1001 0000 0000

C900h

Local Temperature data is represented by an 8-bit, two's complement byte with an LSB (Least Significant Bit)

equal to 1°C:

Temperature

Digital Output

Binary

Hex

+125°C

0111 1101

7Dh

+25°C

0001 1001

19h

+1°C

0000 0001

01h

0°C

0000 0000

00h

−1°C

1111 1111

FFh

−25°C

1110 0111

E7h

−55°C

1100 1001

C9h

9.3.6

Open-Drain Outputs

The SMBData, ALERT and T_CRIT_A 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 provided by some external source, typically a pull-

up resistor. Choice of resistor value depends on many system factors but, in general, the pull-up resistor should

be as large as possible. This will minimize any internal temperature reading errors due to internal heating of the

LM89. The maximum resistance of the pull-up to provide a 2.1V high level, based on LM89 specification for High

Level Output Current with the supply voltage at 3.0V, is 82k

Ω(5%) or 88.7kΩ(1%).

9.3.7 Diode Fault Detection

The LM89 is equipped with operational circuitry designed to detect fault conditions concerning the remote diode.

register is loaded with +127°C, the Remote Temperature Low Byte (RTLB) register is loaded with 0, and the

OPEN bit (D2) in the status register is set. As a result, if the Remote T_CRIT setpoint register (RCS) is set to a

value less than +127°C the ALERT and T_Crit output pins will be pulled low, if the Alert Mask and T_Crit Mask

are disabled. If the Remote HIGH Setpoint High Byte Register (RHSHB) is set to a value less than +127°C then

ALERT will be pulled low, if the Alert Mask is disabled. The OPEN bit itself will not trigger and ALERT.

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