NXP – PCT2075 Family of Thermal Sensors for the I2C Bus

NXP_PCT20xxFamily

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The PCT2075 Family of thermal sensors have a wide range of applications from precision laboratory grade instruments to safety and maintenance monitoring in many industrial systems, and even in wearables. The heart in each case is the sensor IC, which converts local temperatures to digital data sent over the popular I2C bus.

Reliable and repeatable temperature measurement is easy to add to any system using a small footprint mixed-signal IC, called a thermal sensor. The I2C bus (which probably already exists in the design), and a little firmware overhead complete the design. Measurements are made automatically using the well-known Band Gap analog circuit and a high resolution analog to digital converter, all integrated on a single die.

With a temperature measurement range of -25°C to +100°C, a resolution of 0.125°C (11-bits), initial accuracy of ±1°C, very low power consumption of 200μA at 5V, and very small package footprint, thermal sensors excel in even the most demanding applications running on battery power. An added bonus is the shutdown mode, which reduces power consumption to just one micro-amp. Ideal for handheld instruments and wearable personal electronics.

At the other end of the spectrum, for large installations such as cloud storage, servers, and telecom equipment, a thermal sensor IC monitors ambient temperatures. Energy conscious systems can measure temperature rises inside cabinets and plenums, anticipate required air flow, and control variable speed fans that provide cooling while conserving energy.

Demand for multi-point temperature measurements, requiring more than one thermal sensor IC, are easily accommodated thanks to expanded addressing for the individual thermal sensors. This is important for applications such as LED backlighting in large LCD panels, blade PCBs with multiple high density and hot ICs, and high speed memory arrays found in emerging solid state drives (SSDs). The latest thermal sensors offer up to 27 unique addresses using just three address pins on these popular 8-pin devices.

When size is a premium the tiny TSOP6 package is only 2.9 x 1.5 x 1.0mm, yet offers three unique addresses, allowing interconnection of multiple devices on the same I2C bus.

Mixed-signal IC temp sensors have programmable registers for an over-temperature alarm, with a dedicated hardware output. This feature provides a failsafe system shutdown, even if the communication bus or processor monitoring the thermal sensor is disabled as a consequence of the rising temperature fault condition. A programmable ‘queue’ (number of violations before triggering an alarm) stops nuisance tripping of the alarm when temperatures fluctuate around the set trip point.

The industry standard “LM75”, available from several vendors, has been redesigned with the new features described here, as the NXP PCT2075 family. See below for PCT2075 packages shown in comparative sizes.

PCT2075-packages-shown-in-comparative-size

PCT2075DPCT2075DPPCT2075TPPCT2075GV
SO8TSSOP8HWSON8TSOP6
SOT96-1SOT505-1SOT1096-2SOT1353-1
4.9 x 3.9 x 1.253.0 x 3.0 x 1.12.0 x 3.0 x 0.82.9 x 1.5 x 1.0

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FEATURES

  • Pin-for-pin replacement for LM75
  • Power supply range from 2.7V to 5.5V
  • Fast-mode plus I2C interface
  • Stand-by current 1uA, operating current 200uA typical
  • Expanded addresses (27 versus original 8 on LM75)
  • Many package options

BENEFITS

  • Upgrade from an industry standard device
  • Legacy 5V systems, and newer low voltage designs
  • Very low power compared with LM75
  • Strong I2C driver operates on legacy and Fm+ I2C buses
  • Allows a large array of temp sensors on the same bus
  • SO8, TSSOP8, 2 x 3mm HWSON8, and TSOP6

 

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