AN835 Datasheet, PDF(1/4 Page) Silicon Laboratories – COMBINING THREE VERY LOW SUPPLY CURRENT ANALOG ICS INTO A USB-POWERED THERMOSTAT

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AN835 Datasheet, PDF (1/4 Pages) Silicon Laboratories – COMBINING THREE VERY LOW SUPPLY CURRENT ANALOG ICS INTO A USB-POWERED THERMOSTAT

AN835

COMBINING THREE VERY LOW SUPPLY CURRENT

ANALOG ICS INTO A USB-POWERED THERMOSTAT

1. Introduction

In areas where ambient temperatures reach in the high 80 degrees Fahrenheit, such as Central America, South

America, Asia, the Middle East, and certain areas in the United States, a portable fan would help. It may seem

challenging to those new to the world of analog circuits and analog circuit design to conceptualize a solution using

fundamental circuits and ICs; however, the following provides a step-by-step implementation of a basic

temperature-based fan thermostat/controller. This approach makes use of the popular USB port available in many

portable devices to create a USB-powered fan thermostat/controller that can bring relief to the user. By using a

simple temperature sensor coupled with a simple low power circuit that consists of the TS6001-2.5 voltage

reference, the TS1001 low power operational amplifier, and the TS9001 comparator, you may find the design of a

5V USB-powered fan thermostat/controller to be easy, interesting, and useful.

2. Overview

The TS9001-1âs low input offset voltage (VOS) and low input current (IIN+/-) create a circuit with outstanding input

sensitivity while consuming only 0.68ÂµA of supply current. An internal 1.252V reference voltage allows for simple

interface and less components for setting the threshold voltage for the comparator. Its rail-to-rail inputs support a

wide range of input common-mode bias configurations and the widest possible range of input signals. In addition,

the precision dc specifications of the TS1001, such as its low 0.5mV input offset voltage, its low 0.025nA input bias

current, and its high open-loop gain of 90dB all combine to produce an output voltage that represents the input

temperature accurately. The TS6001 2.5-V precision voltage reference operates as a low-dropout regulator in this

circuit and its line regulation performance eliminates the need for additional bypass capacitances on the TS1001

and the TS9001-1. Figure 1 illustrates the complete circuit.

Figure 1. Very Low Supply Current, USB-Powered Thermostat/Fan Controller Circuit

Rev. 1.0 1/15

AN835

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