ZHCST02A September   2023  – December 2023 ISOM8110

PRODUCTION DATA  

  1.   1
  2. 1 特性
  3. 2 应用
  4. 3 说明
  5. 4 Revision History
  6. 5 Device Selection
  7. 6 Pin Configuration and Functions
  8. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Thermal Information
    4. 7.4 Insulation Specifications
    5. 7.5 Safety-Related Certifications
    6. 7.6 Safety Limiting Values
    7. 7.7 Electrical Characteristics
    8. 7.8 Switching Characteristics
    9. 7.9 Typical Characteristics
  9. 8 Parameter Measurement Information
  10. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
    4. 9.4 Device Functional Modes
  11. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Typical Application
        1. 10.1.1.1 Design Requirements
        2. 10.1.1.2 Detailed Design Procedure
        3. 10.1.1.3 Application Curves
    2. 10.2 Power Supply Recommendations
    3. 10.3 Layout
      1. 10.3.1 Layout Guidelines
      2. 10.3.2 Layout Example
  12. 11Mechanical, Packaging, and Orderable Information
    1. 11.1 Tape and Reel Information

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10.1.1.2 Detailed Design Procedure

This section presents the design procedure for using the ISOM811x opto-emulators. External components should be selected to operate ISOM811x within the Recommended Operating Conditions. The following recommendations on component selection focus on the design of a typical feedback control loop for an isolated flyback converter.

When using an optocoupler in a feedback control loop for an isolated power supply, many variables can affect how to properly use the optocoupler, including the output voltage of the power supply and the type of controller the feedback signal is being sent to. For this example, let’s assume the output voltage of this power supply, VOUT, is 5 V, and the PWM controller being used has an integrated error amplifier with a COMP pin that acts as the output of this amplifier.

Sizing RPULLUP

The transistor output of ISOM811x will operate in active, saturation, reverse, and cut-off regions, just like a regular transistor. To ensure the output does not get damaged when it is saturated, the minimum value of RPULLUP can be calculated for a given pull-up voltage, VPULLUP, in Equation 1 below:

Equation 1. RPULLUP> VPULLUP- VCE(SAT)IC(MAX)

For the example of a feedback loop application, we can calculate the minimum required value for RPULLUP for a given VPULLUP of 10 V, the max output voltage of the error amplifier (VCOMP(MAX) of 2.5 V, and the max output current of the error amplifier is internally clamped at 1.6 mA. The equation to calculate RPULLUP is shown in Equation 2 below:

Equation 2. RPULLUP> VPULLUP- VCOMP(MAX)ICOMP(CLAMP)= 10 V - 2.5 V1.6 mA= 4.66 kΩ

Sizing RIN

The input side of ISOM811x is current-driven. To limit the amount of current flowing into the AN pin, it is recommended that a series resistor, RIN, is used in series with the input as shown in Figure 10-1.

Depending on how the ISOM811x device is being used, the value of RIN can vary quite a bit. However, at a high level, to make sure the input does not get damaged, the minimum value of RIN can be calculated for a given input voltage, VIN, in Equation 3 below:

Equation 3. RIN> VIN- VFIC(MAX)

However, in the use case of a feedback loop, RIN directly affects the mid-band gain of the loop. Let’s assume the TL431 has been configured to give a reference voltage, VREF, of 2.5 V and RPULLUP is 5 kΩ. Equation 4 is used to calculate the maximum value of RIN ensuring that VCOMP voltage on the primary side can be pulled to the saturation voltage of the ISOM811x, VCE(SAT).

Equation 4. RIN< (VOUT- VREF-VF) × RPULLUP ×CTRMINVPULLUP - VCE(SAT) = (5 V- 2.5 V-1.2 V) × 5 kΩ ×100%10 V - 0.3 V = 670 Ω