Sensors monitor temperature of computer DIMMs

STMicroelectronics has developed two high-accuracy application specific digital temperature-sensor chips fully compliant with the JEDEC JC42.4 specification. The ICs are intended for monitoring the temperature of DIMMs used in PCs.

The faster DDR2 and DDR3 DRAM memories installed in PCs and other systems increase the risk of memory overheating, so temperature sensing, which allows the CPU to regulate the speed of the memory traffic or take further action to prevent overheating, has become more important in system design.

The STTS424 is a standalone digital temperature sensor, while the STTS424E02 integrates the temperature sensor with a 2Kbit Serial Presence Detect (SPD) EEPROM that is used on DIMMs to store timing parameters and other information about the module based on JEDEC requirements. Both devices communicate with the CPU chipset through an I?C/SMBus-compatible serial bus and are available in 2mm x 3mm DFN8 and 4.4mm x 3mm TSSOP8 packages.

The STTS424 sensor has a 50 percent lower operating current than competitive devices and the JEDEC JC42.4 standard. The integrated STTS424E02 can replace the 2Kbit SPD EEPROM of existing memory module implementations, adding temperature-sensing capability with minimum board redesign cost and with no increase in components. For programming ease, the temperature sensor and the EEPROM in the STTS424E02 each have their own unique I?C/SMBus address.

The sensor chips integrate an ADC which monitors and digitizes the temperature with a resolution down to 0.25°C, and an accuracy of ± 1°C, over the 75°C to 95°C range. The devices are factory-calibrated and require no external components for temperature measurement. They can operate on a supply voltage from 2.7V to 3.6V, and over a -40°C to 125°C temperature range. The typical supply current at 3.3V is 100?A.

An open-drain EVENT output pin is active either if the monitored temperature exceeds a programmed limit or if it strays outside the upper or lower limit of a customer-programmed Alarm window. The pin can be configured to operate either in a comparator mode for thermostat operation, or in the interrupt mode. The 2Kbit serial EEPROM in the STTS424E02 has the ability to permanently lock the data in the first 128bytes, for use in DDR DIMMs with SPD.

Available now for production orders, the STTS424 is priced at 70 cents and the STTS424E02 at 85 cents, in high volume quantities.