When is 2 less than 1? The low power riddle

Every time we use an automatic soap, paper or water dispenser by waving our hands in front of the sensor, the system consumes power from the electronics that allow us to keep things cleaner. These applications, including any energy harvesting system or any other power sensitive applications like battery powered equipment all need to minimize power consumption. Usually it means more integration and fewer parts. So how can more be less when it comes to lowering system power? My colleague Marc Royer's answer is the little 3x3mm2 WQFN packaged ADS7924 that saves the day by allowing the already very low power microcontroller to sleep and saving up to 28% of overall power consumption!

The ADS7924 is a 12 bit SAR ADC which consumes only 0.5mW of power to begin with. It saves on externally component count by integrating 4 input mux so only one ADC is required and only one op amp driver or signal conditioning circuit is required. The onboard oscillator supplies the master clock, eliminating even more components and system power.


Figure 1: Internal Block Diagram of the ADS7924

Intelligent monitoring allows developers to auto-sequence the 4 channel inputs to the mux and digitally set individual threshold levels for each channel. Micro power monitoring sets scan period for the 4 channels. A 1ms scan rate consumes 25µW while a 10ms scan rate consumes only 5µW. If the threshold is exceeded, an alarm is set off causing an interrupt. The microcontroller only wakes up when it is necessary, does its part, and peacefully goes back to sleep.  


Figure 2: Sensor Data Acquisition with and Op Amp Driving an RC Filter (taken from Figure 39 in the datasheet)

Next time you're designing a non-continuous, monitoring system take a second look at your design: you might just be able to dissipate less with ADS7924!

  • How to express "automatic soap" this phrase?

  • hii ma'am i am a postgraduate student . i want to get hands on experience with practical knowledge. i am confused . please do guide from where should i start. i an new to this field..

    .best regards


  • Years ago, I did micropower A/D conversion without needing an ADC at all.  I used a cmos switch on a precision reference driven at a varying duty cycle by a uP i/o port, integrated the difference between the filtered switch wave and the input signal, and applied the integrator output to a micropower schmitt trigger which was input to the uP to adjust the duty cycle.  The uP system and convertor together needed less than 2 milliwatts, tracked a slowly varying signal within 1 part in 3E4, and acquired a full-scale step-change in about 1/2 second by increasing the bias current of the integrator when lock was lost.  It made it possible to build a 4 - 20 mA current loop device that needed less than 6 volts across its terminals to operate.  We patented it in the early '80s, so it's public domain now if anyone has a use for it.