LM93CIMT National Semiconductor, LM93CIMT Datasheet - Page 12

• Manufacturer Part Number: LM93CIMT
• Description: Microprocessor Support IC
• Manufacturer: National Semiconductor

Specifications of LM93CIMT

• Peak Reflow Compatible (260 C): No
• Supply Voltage Max: 3.6V
• Leaded Process Compatible: No
• Supply Voltage Min: 3V
• Operating Temperature Min: 0��C
• Package / Case: 56-TSSOP
• Operating Temperature Max: 85°C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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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
that a nominal voltage appears at
ages and
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.
±
12V. The inputs are converted to 8-bit digital values such
1
⁄
4
scale for negative voltages. The analog inputs
3
⁄
4
scale for positive volt-
12
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:
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.
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
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
reading is achieved when 1.236V is applied to these inputs.
For optimum performance the +12V should be scaled to
Zone 1
Zone 2
Zone 3
Zone 4
Zone
±
Temperature
12V inputs must be scaled externally. A full scale
+125˚C
−127˚C
+1.0˚C
−1.0˚C
+25˚C
−25˚C
−55˚C
0˚C
Processor 1 remote diode
(REMOTE1+, REMOTE1−)
Processor 2 remote diode
(REMOTE2+, REMOTE2−)
Internal LM93 on-chip sensor
External Digital Sensor written in from SMBus
0001 1001
0000 0001
0000 0000
1100 1001
1000 0001
Description
0111 1101
1110 0111
1111 1111
Binary
±
12V. Input voltages
Hex
7Dh
FFh
E7h
C9h
19h
01h
00h
81h