SNOSD29E December   2016  – April 2018 TLV8541 , TLV8542 , TLV8544

UNLESS OTHERWISE NOTED, this document contains PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Low Power PIR Motion Detector
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
    1.     Pin Functions: TLV8541 DBV
    2.     Pin Functions: TLV8542 D & RUG
    3.     Pin Functions: TLV8544 PW & D
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
    4. 8.4 Device Functional Modes
      1. 8.4.1 Rail-To-Rail Input
      2. 8.4.2 Supply Current Changes Over Common Mode
      3. 8.4.3 Design Optimization With Rail-To-Rail Input
      4. 8.4.4 Design Optimization for Nanopower Operation
      5. 8.4.5 Common-Mode Rejection
      6. 8.4.6 Output Stage
      7. 8.4.7 Driving Capacitive Load
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application: Battery-Powered Wireless PIR Motion Detectors
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Calculation of the Cutoff Frequencies and Gain of Stage A:
        2. 9.2.2.2 Calculation of the Cutoff Frequencies and Gain of Stage B
        3. 9.2.2.3 Calculation of the Total Gain of Stages A and B
        4. 9.2.2.4 Window Comparator Stage
        5. 9.2.2.5 Reference Voltages
      3. 9.2.3 Application Curve
    3. 9.3 Typical Application: 60-Hz Twin T Notch Filter
      1. 9.3.1 Design Requirements
      2. 9.3.2 Detailed Design Procedure
      3. 9.3.3 Application Curve
    4. 9.4 Dos and Don'ts
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Related Links
    4. 12.4 Receiving Notification of Documentation Updates
    5. 12.5 Community Resources
    6. 12.6 Trademarks
    7. 12.7 Electrostatic Discharge Caution
    8. 12.8 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.2.4 Window Comparator Stage

The signal from a moving object in front of the PIR sensor, after amplification and filtering, is connected to a window comparator. The comparator converts the analog signal to digital pulses for interrupting an on-board microcontroller unit (MCU), flagging detection of motion. A different approach is to digitize the analog signal continuously by an analog-to-digital converter (ADC) and implement the comparator functionality in the digital domain. This method has the advantage of enabling the post processing of the data to reduce the chance of false detection. However, continuous conversion and processing of data by the MCU increases the power consumption, lowering the lifetime of the battery substantially.

Rather than using a separate low-power comparator integrated circuits to implement the window comparator section of the circuit, the remaining op amps in the TLV8544 package are used to implement the comparator stage. Benefits of this approach include fewer components and thus reduced system cost.

Although an op amp can sometimes be used as a comparator, an amplifier cannot be used as a comparator interchangeably in all applications because of relatively long recovery time of the amplifier from output saturation and relatively long propagation delay due to internal compensation. Particularly, the nanopower op amps have very slow slew rate, limiting their usage as a comparator in only applications with very low frequency input signal. Fortunately, PIR sensor signals are relatively slow and this should not be an issue.

The new TLV8544 device is particularly suitable for implementing a window comparator in a battery operated PIR motion detector application because of its rail-to-rail operation capability, relatively low offset voltage, low offset voltage drift, very low bias current, and nanopower consumption, all at an optimal cost. The input signal of the comparator stage in the presence of moving heat source across the sensor is shown in Figure 33. The signal is centered at mid-rail and can swing up or down from the center.

The window comparator is a combination of a non-inverting comparator implemented with amplifier D and an inverting comparator implemented with amplifier C, as shown in Figure 32.

TLV8544 TLV8542 TLV8541 PIRsignal-SNAA301-01.gifFigure 33. Ideal Amplified PIR Signal and the Output of the Window Comparator Circuit