National Semiconductor introduced a family of remote-diode temperature sensors that employ the companies TruTherm thermal management technology with transistor-mode beta compensation. The technology solves the problem of inaccurate remote temperature readings caused by variations in the internal diodes in deep sub-micron microprocessors, microcontrollers, application-specific integrated circuits (ASICs) and field-programmable gate arrays (FPGAs). Inaccurate remote temperature readings can lead to higher acoustic noise and reduced system performance.
The Hardware Monitor
The LM94 hardware monitor has a two-wire digital interface that is compatible with system management bus (SMBus) 2.0. Using a sigma-delta analog- to-digital converter (ADC), the LM94 measures the temperature of up to four remote-diode-connected transistors as well as its own die, and up to 16 power supply voltages supporting dual processors. To set fan speed, the LM94 has two pulse-width modulation (PWM) outputs that are each controlled by up to six temperature zones. The fan-control algorithm can be based on a lookup table, a proportional/integral (PI) control loop that supports a temperature control (Tcontrol) function or a combination of both. The LM94 includes digital filters to smooth temperature readings for better control of fan speed, minimizing acoustical noise. The LM94 has four tachometer inputs to measure fan speed and includes limit and status registers for all measured values. It also supports monitoring of the dynamic power supply voltage for the processor (VccP), dual processor thermal throttling monitoring (PROCHOT) functions and general purpose input/output (I/O) pins.
The Remote-Diode Temperature Sensors
Four-Diode Sensing: LM95234
The LM95234 is an 11-bit digital temperature sensor with a two-wire SMBus interface that monitors the temperature of four remote diodes as well as its own temperature. The LM95234 supports three critical temperature (TCRIT) outputs with individual limits for each channel and masking capability. Two of the LM95234's remote temperature channels have programmable digital filters, while the other two channels utilize a fault queue to avoid falsely triggering the TCRIT pins if the temperature of a channel momentarily goes above the corresponding limit.
Two-Diode Sensing: LM95241 and LM95233
The LM95241 is a precision, dual remote-diode temperature sensor with a two-wire serial interface that is compatible with SMBus 2.0. The LM95241 senses three temperature zones, two remote diodes and its own temperature. It has digital filtering and an advanced input stage that includes analog filtering. The LM95241 resolution format for remote temperature readings can be programmed to be 11-bits signed or unsigned with the digital filtering disabled. When the filtering is enabled, the resolution increases to 13-bits signed or unsigned. In unsigned mode, the LM95241 remote diode readings can resolve temperatures above 127 degrees C. Local temperature readings have a resolution of 9-bits plus sign. The LM95233 is a two-diode version of the LM95234.
Single-Diode Sensing: LM95235
The LM95235 is an 11-bit digital temperature sensor with a two-wire SMBus interface that monitors the temperature of a single remote diode as well as its own temperature. The LM95235 features programmable TCRIT and OS thresholds, and can be used to shut down the system, turn on system fans or as a microcontroller interrupt function. The LM95235 is pin compatible with National Semiconductor's industry-standard LM86 and LM89.
Pricing and Availability
Prices for the products start at $1.17 for the LM95241 in 1,000-unit quantities. The LM94 and LM95235 are available now. The LM95233, LM95234 and LM95241 will be available later this fall and are currently sampling.
