SNOSAI6J September   2005  – August 2016 LPV7215

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics: 1.8 V
    6. 6.6 Electrical Characteristics: 2.7 V
    7. 6.7 Electrical Characteristics: 5 V
    8. 6.8 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Input Stage
      2. 7.3.2 Output Stage
      3. 7.3.3 Output Current
      4. 7.3.4 Response Time
    4. 7.4 Device Functional Modes
      1. 7.4.1 Capacitive and Resistive Loads
      2. 7.4.2 Noise
      3. 7.4.3 Hysteresis
      4. 7.4.4 Inverting Comparator With Hysteresis
      5. 7.4.5 Noninverting Comparator With Hysteresis
      6. 7.4.6 Zero Crossing Detector
      7. 7.4.7 Threshold Detector
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Square Wave Generator
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Window Detector
      3. 8.2.3 Crystal Oscillator
      4. 8.2.4 IR Receiver
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
      2. 11.1.2 Documentation Support
        1. 11.1.2.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LPV7215 is an ultra-low-power comparator with a typical power supply current of 580 nA. It has the best-in-class power supply current versus propagation delay performance available among TI's low-power comparators. The propagation delay is as low as 4.5 µs with 100-mV overdrive at 1.8-V supply.

8.2 Typical Applications

8.2.1 Square Wave Generator

LPV7215 20123638.gif Figure 37. Square Wave Generator Schematic

8.2.1.1 Design Requirements

A typical application for a comparator is as a square wave oscillator. The circuit in Figure 38 generates a square wave whose period is set by the RC time constant of the capacitor C1 and resistor R4. The maximum frequency is limited by the large signal propagation delay of the comparator and by the capacitive loading at the output, which limits the output slew rate.

8.2.1.2 Detailed Design Procedure

LPV7215 20123639.png Figure 38. Square Wave Oscillator

Consider the output of Figure 38 to be high to analyze the circuit. That implies that the inverted input (VC) is lower than the noninverting input (VA). This causes the C1 to be charged through R4, and the voltage VC increases until it is equal to the noninverting input. The value of VA at this point is in Equation 8.

Equation 8. LPV7215 20123640.gif

If R1 = R2 = R3 then VA1 = 2 VCC/3

At this point the comparator switches pulling down the output to the negative rail. The value of VA at this point, as shown in Equation 9:

Equation 9. LPV7215 20123641.gif

If R1 = R2 = R3 then VA2 = VCC/3

The capacitor C1 now discharges through R4, and the voltage VC decreases until it is equal to VA2, at which point the comparator switches again, bringing it back to the initial stage. The time period is equal to twice the time it takes to discharge C1 from 2 VCC/3 to VCC/3, which is given by R4C1 × ln2. Hence the formula for the frequency is given by Equation 10:

Equation 10. F = 1/(2 × R4 × C1 × ln2)

8.2.1.3 Application Curves

Figure 39 shows the simulated results of an oscillator using the following values:

  1. R1 = R2 = R3 = R4 = 100 kΩ
  2. C1 = 100 pF, CL = 20 pF
  3. V+ = 5 V, V– = GND
  4. CSTRAY (not shown) from Va to GND = 10 pF

LPV7215 D001_SNOSAI6.gif
Figure 39. Square Wave Oscillator Output Waveform

8.2.2 Window Detector

A window detector monitors the input signal to determine if it falls between two voltage levels.

The comparator outputs A and B are high only when VREF1 < VIN < VREF2 or within the window. These are defined as:

Equation 11. VREF1 = R3 / (R1+ R2 + R3) × V+
Equation 12. VREF2 = (R2+ R3) / (R1 + R2 + R3) × V+

Others names for window detectors are: threshold detector, level detectors, and amplitude trigger or detector.

LPV7215 20123647.gif Figure 40. Window Detector
LPV7215 20123648.gif Figure 41. Window Detector Output Signal

8.2.3 Crystal Oscillator

A simple crystal oscillator using the LPV7215 is shown in Figure 42. Resistors R1 and R2 set the bias point at the comparator’s noninverting input. Resistors, R3 and R4 and capacitor C1 set the inverting input node at an appropriate DC average level based on the output. The crystal’s path provides resonant positive feedback and stable oscillation occurs. The output duty cycle for this circuit is roughly 50%, but it is affected by resistor tolerances and to a lesser extent by the comparator offset.

LPV7215 20123631.gif Figure 42. Crystal Oscillator

8.2.4 IR Receiver

The LPV7215 can also be used as an infrared receiver. The infrared photo diode creates a current relative to the amount of infrared light present. The current creates a voltage across RD. When this voltage level crosses the voltage applied by the voltage divider to the inverting input, the output transitions.

LPV7215 20123632.gif Figure 43. IR Receiver