LM93 datasheet(12/92 Pages) NSC

12 / 92 page

12.0 Functional Description

The LM93 provides 16 channels of voltage monitoring, two

remote thermal diode monitors, an onboard ambient tem-

perature sensor, 2 PROCHOT monitors, 4 fan tachometers,

8 GPIOs, THERMTRIP monitor for masking error events, 2

SCSI_TERM inputs, and all the associated limit registers on

a single chip, which communicates to the rest of the base-

board over the System Management Bus (SMBus).

Readings from both the external thermal diodes and the

internal temperature sensor are made available as an 8-bit

two’s-complement digital byte with the LSB representing

1˚C.

All but 4 of the analog inputs include internal scaling resis-

tors. External scaling resistors are required for measuring

±12V. The inputs are converted to 8-bit digital values such

that a nominal voltage appears at 3⁄4 scale for positive volt-

ages and 1⁄4 scale for negative voltages. The analog inputs

are intended to be connected to both baseboard resident

VRDs and to standard voltage rails supplied by a SSI com-

pliant power supply.

The LM93 provides a number of internal registers, which are

detailed in the register section of this document.

12.1 MONITORING CYCLE TIME

When the LM93 is powered up, it cycles through each tem-

perature measurement followed by the analog voltages in

sequence, and it continuously loops through the sequence.

The total monitoring cycle time is not more than 100 ms, as

this is the time period that most external micro-controllers

require to read the register values.

Each measured value is compared to values stored in the

limit registers. When the measured value violates the pro-

grammed limit, a corresponding status bit in the B_ and

H_Error Status Registers is set.

The PROCHOT and dynamic VID/Vccp monitoring is per-

formed independently of the analog and temperature moni-

toring cycle.

12.2

Σ∆ A/D INHERENT AVERAGING

The

Σ∆ A/D architecture filters the input signal. During one

conversion many samples are taken of the input voltage and

these samples are effectively averaged to give the final

result. The output of the

Σ∆ A/D is the average value of the

signal during the sampling interval. For a voltage measure-

ment, the samples are accumulated for 1.5 ms. For a tem-

perature measurement, the samples are accumulated for

8.4 ms.

12.3 TEMPERATURE MONITORING

The LM93 remote diode target is the embedded thermal

diode found in a Xeon class processor. In some cases

instead of using the embedded thermal diode, found on the

Xeon processor, a diode connected 2N3904 transistor type

can also be used. An example of this would be a MMBT3904

with its collector and base tied to the thermal diode RE-

MOTE+ pin and the emitter tied to the thermal diode

REMOTE− pin. Since the MMBT3904 is a surface mount

device and has very small thermal mass, it measures the

board temperature where it is mounted. The non-ideality and

series resistance varies for different diodes. Since the LM93

is optimized for the Xeon processor, when measuring a

2N3904 transistor an offset in the error band of approxi-

mately −4˚C may be observed. This can be corrected for by

programming the appropriate Zone Adjustment Offset regis-

ter.

The LM93 acquires temperature data from three different

sources:

2 external diodes (embedded in a processor or discrete)

1 internal diode (internal to the LM93)

In addition to these three temperatures, a fourth temperature

can be externally written into the LM93 from the SMBus. This

value can be used to control fans, or compared against

limits, etc. The temperature value registers are located at

addresses 50h–53h. The temperature sources are referred

to as “zones” for convenience:

Zone

Description

Zone 1

Processor 1 remote diode

(REMOTE1+, REMOTE1−)

Zone 2

Processor 2 remote diode

(REMOTE2+, REMOTE2−)

Zone 3

Internal LM93 on-chip sensor

Zone 4

External Digital Sensor written in from SMBus

12.3.1 Temperature Data Format

Most of the temperature data for the LM93 is represented in

a common format. The format is an 8-bit, twos complement

byte with the LSB equal to 1.0 ˚C. This applies to tempera-

ture measurements as well as any temperature limit regis-

ters and some configuration registers. Some fan control

configuration registers use four bits and have a binary for-

mat, please see the fan control configuration register de-

scriptions for further details on this 4-bit format.

Temperature

Binary

Hex

+125˚C

0111 1101

7Dh

+25˚C

0001 1001

19h

+1.0˚C

0000 0001

01h

0˚C

0000 0000

00h

−1.0˚C

1111 1111

FFh

−25˚C

1110 0111

E7h

−55˚C

1100 1001

C9h

−127˚C

1000 0001

81h

Note: A value of 80h has a special meaning in the limit registers. It means

that the temperature channel is masked. In addition, temperature readings of

80h indicate thermal diode faults.

12.3.2 Thermal Diode Fault Status

The LM93 provides for indications of a fault (open or short

circuit) with the remote thermal diodes. Before a remote

diode conversion is updated, the status of the remote diode

is checked for an open or short circuit condition. If such a

fault condition occurs, a status bit is set in the status register.

A short circuit is defined as the input pins being connected to

each other. When an open or short circuit is detected, the

corresponding temperature register is set to 80h.

12.4 VOLTAGE MONITORING

The LM93 contains inputs for monitoring voltages. Scaling is

such that the correct value refers to approximately 3/4 scale

or 192 decimal on all inputs except the ±12V. Input voltages

are converted by an 8-bit Delta-Sigma (

∆Σ) A/D. The Delta-

Sigma A/D architecture provides inherent filtering and spike

smoothing of the analog input signal.

The ±12V inputs must be scaled externally. A full scale

reading is achieved when 1.236V is applied to these inputs.

For optimum performance the +12V should be scaled to

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