SLOS805C July   2012  – August 2016 OPA1662-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description Continued
  6. 6 Pin Configuration and Functions
  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: VS = ±15 V
    6. 7.6 Electrical Characteristics: VS = 5 V
    7. 7.7 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Operating Voltage
      2. 8.3.2 Input Protection
      3. 8.3.3 Noise Performance
      4. 8.3.4 Basic Noise Calculations
      5. 8.3.5 Total Harmonic Distortion Measurements
      6. 8.3.6 Capacitive Loads
      7. 8.3.7 Electrical Overstress
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Power Dissipation
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

9 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.

9.1 Application Information

The OPA1662-Q1 is a unity-gain stable, precision dual op amp with very low noise. Applications with noisy or high-impedance power supplies require decoupling capacitors close to the device pins. In most cases, 0.1-µF capacitors are adequate. Figure 43 shows a simplified schematic of the OPA1662-Q1 (one channel shown) while Figure 49 shows an additional application idea.

9.2 Typical Application

OPA1662-Q1 ai_audio_dac_bos489_v2.gif Figure 49. Audio DAC Current to Voltage Converter and Output Filter

9.2.1 Design Requirements

Table 1 lists the design parameters for this example.

Table 1. Design Parameters

PARAMETER EXAMPLE VALUE
Supply voltage ±15 V to ±36 V
Differential input currents 0 mA to 30 mA
Resistors value tolerance 1%
Ceramic capacitor XR5 or XR7 50 V

9.2.2 Detailed Design Procedure

This circuit is designed for converting differential input current into a single ended output voltage. The resistor values are chosen to be relatively low for minimizing the total circuit noise. The filtering capacitors are chosen to maintain adequate bandwidth from 10 Hz to 20 kHz for audio signals.

The first stage converts the audio DAC output current into a voltage with a gain calculated by Equation 1:

Equation 1. OPA1662-Q1 eq_1_SLOS805.gif

where

  • R = 820 Ω
  • C = 2200 pF
  • S is Laplace variable

RC filters the audio DAC output ripple and cutoff frequency = OPA1662-Q1 eq_2_SLOS805.gif = 80 KHz

The second differential stage transfer function is calculated by Equation 2:

Equation 2. OPA1662-Q1 eq_3_SLOS805.gif

The denominator of this transfer function OPA1662-Q1 eq_4_SLOS805.gif is a quadratic equation and the general form is calculated by Equation 3:

Equation 3. OPA1662-Q1 eq_5_SLOS805.gif

where

  • ωo = 2πFo is the resonance frequency
  • and Q is the quality factor

The gain peak depends on the quality factor in Equation 4:

Equation 4. OPA1662-Q1 eq_6_SLOS805.gif

The resonance frequency is calculated by Equation 5:

Equation 5. OPA1662-Q1 eq_7_SLOS805.gif

These equations help to maintain adequate bandwidth and keep the differential gain flat so the quality factor is from 0.7 to 1. The resonance frequency must be at least twice the desired bandwidth.

The chosen components give a quality factor of 0.89 and a resonance frequency of 53 KHz.

The overall transfer function is shown in Equation 6:

Equation 6. OPA1662-Q1 eq_8_SLOS805.gif

The OPA1662-Q1 eq_10_SLOS805.gif and is 398 mV/mA.

The poles are at 53 KHz and 80 KHz.

9.2.3 Application Curves

OPA1662-Q1 app_curve_1_SLOS805.png
CH1 = positive input current IOUTL+ = 1.5 V / 150 Ω
CH2 = negative input current IOUTL– = 1.5 V / 150 Ω
CH3 = output single-ended voltage
Figure 50. Output Voltage at 10 mApp and 10 Hz
OPA1662-Q1 app_curve_2_SLOS805.png
CH1 = positive input current IOUTL+ = 1.5 V / 150 Ω
CH2 = negative input current IOUTL– = 1.5 V / 150 Ω
CH3 = output single-ended voltage
Figure 51. Output Voltage at 10 mApp and 20 KHz