SLVSDQ6A July 2018 – November 2018 TL431LI , TL432LI

PRODUCTION DATA.

- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Device Comparison Table
- 6 Pin Configuration and Functions
- 7 Specifications
- 8 Parameter Measurement Information
- 9 Detailed Description
- 10Applications and Implementation
- 11Power Supply Recommendations
- 12Layout
- 13Device and Documentation Support
- 14Mechanical, Packaging, and Orderable Information

- DBZ|3

*Figure 26* shows the simplified version of the feedback network. The accuracy of the output voltage is dependent on the regulation voltage accuracy of the TL431LI. A simplified V_{OUT} can be seen in Equation 2 but this equation does not include errors that will deviate the output.

Equation 2.

The primary sources of error are the Error|_{Vref} and Error|_{Iref}. The Error|_{Vref} primarily consists of the errors that affect the internal bandgap voltage reference of the TL431LI. This consists of errors from the initial accuracy, temperature drift, ratio of change in reference voltage to the change in cathode voltage, and dynamic impedance. The benefit of the TL431LI is its low temperature drift, V_{I(dev)}, which allows the V_{ref} to be more accurate across the full temperature range compared to typical TL431LI devices. Equation 3 shows a simplified worst case V_{ref} with initial accuracy and temperature drift.

Equation 3.

The Error|_{Iref} in *Figure 26* is dependent on the I_{ref} and I_{I(dev)} along with R1. The TL431LI has improved I_{ref} and I_{I(dev)} which allows the values of the resistor R1 to be increased to save power. Typically optocoupler feedback design requires the I_{ref} to be taken into account when doing V_{OUT} calculations but the error comes from the deviation from the maximum to typical value of I_{ref}. In addition to this, the I_{I(dev)} is the temperature deviation on the I_{ref} current which will affect the overall reference current into the TL431LI. Equation 4 shows the V_{OUT} of the TL431LI for *Figure 26* which includes the improved I_{ref} and I_{I(dev)}. The V_{OUT} equation assumes that the resistors R1 and R2 have a 0.5% accuracy tolerance.

Equation 4.

Comparing the calculated V_{OUT} without and without error the expected worst case max error is 2.1% which meets the 3% error target.