SLVSCV5D March   2015  – October 2016 ATL431 , ATL432

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, ATL431Ax, ATL432Ax
    6. 6.6 Electrical Characteristics, ATL431Bx, ATL432Bx
    7. 6.7 Typical Characteristics
  7. 7 Parameter Measurement Information
  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 Open Loop (Comparator)
      2. 8.4.2 Closed Loop
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Comparator With Integrated Reference (Open Loop)
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Basic Operation
          2. 9.2.1.2.2 Overdrive
          3. 9.2.1.2.3 Output Voltage and Logic Input Level
            1. 9.2.1.2.3.1 Input Resistance
        3. 9.2.1.3 Application Curve
      2. 9.2.2 Shunt Regulator/Reference
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
          1. 9.2.2.2.1 Programming Output/Cathode Voltage
          2. 9.2.2.2.2 Total Accuracy
          3. 9.2.2.2.3 Stability
        3. 9.2.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Related Links
    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

Package Options

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

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

Figure 29 shows the ATL43x used in a 24-V isolated flyback supply. The output of the regulator, plus the forward voltage drop of the optocoupler LED (2.5 + 0.7 = 3.2 V), determine the minimum voltage that can be regulated in an isolated supply configuration. Regulated voltage as low as 5.0 Vdc is possible in the topology shown in Figure 29.

The 431 family of devices are prevalent in these applications, being designers go-to choice for secondary side regulation. Due to this prevalence, this section will further go on to explain operation and design in both states of ATL43x that this application will see, open loop (Comparator + Vref) and closed loop (Shunt Regulator).

ATL43x's key benefit in isolated supplies is the no load power savings gained by the > 20x decrease in IKmin from TL431. More information about this and other benefits can be found in Designing with the "Advanced" TL431, ATL431, SLVA685. Further information about system stability and using a ATL43x device for compensation can be found in Compensation Design With TL431 for UCC28600, SLUA671.

ATL431 ATL432 flyback_atl.gif Figure 29. Flyback With Isolation Using ATL43x
as Voltage Reference and Error Amplifier

9.2 Typical Applications

9.2.1 Comparator With Integrated Reference (Open Loop)

ATL431 ATL432 comparator_app.gif Figure 30. Comparator Application Schematic

9.2.1.1 Design Requirements

For this design example, use the parameters listed in Table 1 as the input parameters.

Table 1. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
Input voltage range 0 V to 3.3 V
Input resistance 100 kΩ
Supply voltage 5 V
Cathode current (IK) 50 µA
High output voltage level (Vin < 2.5 V) Vsup
Low output voltage (Vin > 2.5 V) ~2 V

9.2.1.2 Detailed Design Procedure

When using ATL43x as a comparator with reference, determine the following:

  • Input voltage range
  • Reference voltage accuracy
  • Output logic input high and low level thresholds
  • Current source resistance

9.2.1.2.1 Basic Operation

In the configuration shown in Figure 30 ATL43x will behave as a comparator, comparing the Vref pin voltage to the internal virtual reference voltage. When provided a proper cathode current (Ik), ATL43x will have enough open loop gain to provide a quick response. With the ATL43x's max operating current (Imin) being 35 µA and up to 40 µA over temperature, operation below that could result in low gain, leading to a slow response.

9.2.1.2.2 Overdrive

Slow or inaccurate responses can also occur when the reference pin is not provided enough overdrive voltage. This is the amount of voltage that is higher than the internal virtual reference. The internal virtual reference voltage will be within the range of 2.5 V ±(0.5% or 1.0%) depending on which version is being used.

The more overdrive voltage provided, the faster the ATL43x will respond.

For applications where ATL43x is being used as a comparator, it is best to set the trip point to greater than the positive expected error (that is, +1.0% for the A version). For fast response, setting the trip point to > 10% of the internal Vref should suffice. Figure 31 shows the transition from VOH to VOL based on the input voltage and can be used as a guide for selecting the overdrive voltage.

For minimal voltage drop or difference from Vin to the ref pin, it is recommended to use an input resistor < 1 MΩ to provide Iref.

9.2.1.2.3 Output Voltage and Logic Input Level

In order for ATL43x to properly be used as a comparator, the logic output must be readable by the receiving logic device. This is accomplished by knowing the input high and low level threshold voltage levels, typically denoted by VIH and VIL.

As seen in Figure 31, ATL43x's output low level voltage in open-loop/comparator mode is ~2 V, which is sufficient for some ≥ 5.0 V supplied logic. However, would not work for 3.3 V and 1.8 V supplied logic. In order to accommodate this, a resistive divider can be tied to the output to attenuate the output voltage to a voltage legible to the receiving low voltage logic device.

ATL43x's output high voltage is approximately Vsup due to ATL43x being open-collector. If Vsup is much higher than the receiving logic's maximum input voltage tolerance, the output must be attenuated to accommodate the outgoing logic's reliability.

When using a resistive divider on the output, be sure to make the sum of the resistive divider (R1 and R2 in Figure 30) is much greater than Rsup in order to not interfere with ATL43x's ability to pull close to Vsup when turning off.

9.2.1.2.3.1 Input Resistance

ATL43x requires an input resistance in this application in order to source the reference current (Iref) needed from this device to be in the proper operating regions while turning on. The actual voltage seen at the ref pin will be:

Equation 1. Vref = Vin – Iref × Rin

Because Iref can be as high as 0.15 µA, TI recommends to use a resistance small enough that will mitigate the error that Iref creates from Vin. Also, the input resistance must be set high enough as to not surpass the absolute maximum of 10 mA.

9.2.1.3 Application Curve

ATL431 ATL432 comp_plot.gif
RIN = 100 kΩ VSUP = 5.0 V RSUP = 10 kΩ
Figure 31. Open Loop (Comparator Mode) VOUT vs VIN

9.2.2 Shunt Regulator/Reference

ATL431 ATL432 shunt_app.gif Figure 32. Shunt Regulator Schematic

9.2.2.1 Design Requirements

For this design example, use the parameters listed in Table 2 as the input parameters.

Table 2. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
Reference initial accuracy 1.0%
Supply voltage 48 V
Cathode current (IK) 50 µA
Output voltage level 2.5 V to 36 V
Load capacitance 1 nF
Feedback resistor values (R1 and R2) 10 kΩ

9.2.2.2 Detailed Design Procedure

When using ATL43x as a Shunt Regulator, determine the following:

  • Input voltage range
  • Temperature range
  • Total accuracy
  • Cathode current
  • Reference initial accuracy
  • Output capacitance

9.2.2.2.1 Programming Output/Cathode Voltage

In order to program the cathode voltage to a regulated voltage a resistive bridge must be shunted between the cathode and anode pins with the mid point tied to the reference pin. This can be seen in Figure 32, with R1 and R2 being the resistive bridge. The cathode/output voltage in the shunt regulator configuration can be approximated by the equation shown in Figure 32. The cathode voltage can be more accurately determined by taking in to account the cathode current:

Equation 2. VO = (1 + R1 / R2) × Vref – Iref × R1

For this equation to be valid, ATL43x must be fully biased so that it has enough open loop gain to mitigate any gain error. This can be done by meeting the Imin spec denoted in Electrical Characteristics, ATL431Ax, ATL432Ax table.

9.2.2.2.2 Total Accuracy

When programming the output above unity gain (VKA = Vref), ATL43x is susceptible to other errors that may effect the overall accuracy beyond Vref. These errors include:

  • R1 and R2 accuracies
  • VI(dev) - Change in reference voltage over temperature
  • ΔVref / ΔVKA - Change in reference voltage to the change in cathode voltage
  • |zKA| - Dynamic impedance, causing a change in cathode voltage with cathode current

Worst case cathode voltage can be determined taking all of the variables in to account. Setting the Shunt Voltage on an Adjustable Shunt, SLVA445, assists designers in setting the shunt voltage to achieve optimum accuracy for this device.

9.2.2.2.3 Stability

Though ATL43x is stable with no capacitive load, the device that receives the shunt regulator's output voltage could present a capacitive load that is within the ATL43x region of stability, shown in Figure 14 through Figure 21. Also, designers may use capacitive loads to improve the transient response or for power supply decoupling.

Figure 14 through Figure 21 should be used as a guide for capacitor selection and compensation. It is characterized using ceramic capacitors with very-low ESR. When it is desirable to use a capacitor within the unstable region, higher ESR capacitors can be used to stabilize ATL43x or an external series resistance can be added. For more information and guidance on ESR values, see Designing with the "Advanced" TL431, ATL431, SLVA685.

Unlike TL431, the stability boundary is characterized and determined with resistors 250 Ω and greater. Which is more suitable for low cathode current applications.

9.2.2.3 Application Curves

ATL431 ATL432 pulse_50ua.gif
Figure 33. ATL43x Start-up Response IKA = 50 µA
ATL431 ATL432 pulse1ma.gif
Figure 34. ATL43x Start-up Response IKA = 1 mA