20112407

Note: 100 pF cap across each thermal diode is optional and should be placed close to the LM94, if used. The maximum capacitance between thermal diode

pins is 300 pF.

Thermal diode recommended implementation

11.0 Functional Description

The LM94 provides 16 channels of voltage monitoring, 4

remote thermal diode monitors, an internal/local ambient

temperature sensor, 2 PROCHOT monitors, 4 fan tachom-

eters, 8 GPIOs, THERMTRIP monitor for masking error

events, 2 sets of 7 VID inputs, an ALERT output and all the

associated limit registers on a single chip, and communi-

cates to the rest of the baseboard over the System Manage-

ment Bus (SMBus). The LM94 also provides 2 PWM outputs

and associated fan control logic for controlling the speed of

system fans. There are two sets of fan control logic, a lookup

table and a PI (proportional/integral) loop controller. The

lookup table and PI controller are interactive, such that the

fans run at the fastest required speed. Upon a temperature

or fan tach error event, the PWM outputs may be pro-

grammed such that they automatically boost to 100% duty

cycle. A timer is included that sets the minimum time that the

fans are in the boost condition when activated by a fan tach

error.

The LM94 incorporates National Semiconductor’s TruTherm

technology for precision “Remote Diode” readings of proces-

sors on 90nm process geometry or smaller. Readings from

the external thermal diodes and the internal temperature

sensor are made available as an 9-bit two’s-complement

digital value with the LSb representing 0.5˚C. Filtered tem-

perature

readings

are

available

as

a

12-bit

two’s-

complement

digital

value

with

the

LSb

representing

0.0625˚C.

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

tors. External scaling resistors are required for measuring

are intended to be connected to both baseboard resident

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

pliant power supply.

The LM94 has logic that ties a set of dynamically moving VID

inputs to their associated Vccp analog input for real time

window comparison fault determination. Voltage mapping for

VRD10, VRD10 extended and VRD11are supported by the

LM94. When VRD10 mode is selected GPI8 and GPI9 can

be used to detect external error flags whose state is be

reflected in the status registers.

Error events are captured in two sets of mirrored status

registers (BMC Error Status Registers and Host Status Reg-

isters) allowing two controllers access to the status informa-

tion without any interference.

The LM94’s ALERT output supports interrupt mode or com-

parator mode of operation. The comparator mode is only

functional for thermal monitoring.

The LM94 provides a number of internal registers, which are

detailed in the register section of this document.

12.0 Please contact your local sales office for complete LM94 applications

information.

13.0 Registers

13.1 REGISTER WARNINGS

In most cases, reserved registers and register bits return zero when read. This should not be relied upon, since reserved registers

can be used for future expansion of the LM94 functions.

Some registers have “N/D” for their default value. This means that the power-up default of the register is not defined. In the case

of value registers, care should be taken to ensure that software does not read a value register until the associated measurement

function has acquired a measurement. This applies to temperatures, voltages, fan RPM, and PROCHOT monitoring.

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