LM93 datasheet(9/95 Pages) TI1

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LM93

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SNAS210E – DECEMBER 2003 – REVISED MARCH 2013

Functional Description

The LM93 provides 16 channels of voltage monitoring, two remote thermal diode monitors, an onboard

ambient temperature 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 baseboard 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 resistors. External scaling resistors are required for

measuring ±12V. The inputs are converted to 8-bit digital values such that a nominal voltage appears at ¾

scale for positive voltages and ¼ 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 compliant

power supply.

The LM93 provides a number of internal registers, which are detailed in the Registers section of this

document.

3.1

MONITORING CYCLE TIME

When the LM93 is powered up, it cycles through each temperature 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

Each measured value is compared to values stored in the limit registers. When the measured value

violates the programmed limit, a corresponding status bit in the B_ and H_Error Status Registers is set.

The PROCHOT and dynamic VID/Vccp monitoring is performed independently of the analog and

temperature monitoring cycle.

3.2

ΣΔ A/D INHERENT AVERAGING

The

ΣΔ 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

ΣΔ A/D

is the average value of the signal during the sampling interval. For a voltage measurement, the samples

are accumulated for 1.5 ms. For a temperature measurement, the samples are accumulated for 8.4 ms.

3.3

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 REMOTE+ 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 approximately

−4°C may be observed. This can be corrected for by programming the appropriate

Zone Adjustment Offset register.

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:

Functional Description

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