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LM94CIMTX Datasheet(PDF) 9 Page - National Semiconductor (TI) |
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LM94CIMTX Datasheet(HTML) 9 Page - National Semiconductor (TI) |
9 / 24 page 10.0 Recommended Implementation (Continued) 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 ±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 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. www.national.com 9 |
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