TL431ACLPR datasheet(24/85 Pages) TI2

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9.2.1.1 Design Requirements

For this design example, use the parameters listed in Table 9-1 as the input parameters.

Table 9-1. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Input Voltage Range

0Vto 5V

Input Resistance

10kΩ

Supply Voltage

24V

Cathode Current (Ik)

5mA

Output Voltage Level

~2V– VSUP

Logic Input Thresholds VIH/VIL

9.2.1.2 Detailed Design Procedure

When using TL431 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 9-1 TL431 will behave as a comparator, comparing the VREF pin voltage

to the internal virtual reference voltage. When provided a proper cathode current (IK), TL43xx will have enough

open loop gain to provide a quick response. This can be seen in Figure 9-2, where the RSUP=10 kΩ (IKA=500 µA)

situation responds much slower than RSUP=1 kΩ (IKA=5mA). Operation near and below Imin could result in low

gain, leading to a slow response.

9.2.1.2.1.1 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 2.5V±(0.5%, 1.0% or 1.5%) depending on which version is being used. The

more overdrive voltage provided, the faster the TL431 will respond.

For applications where TL431 is being used as a comparator, it is best to set the trip point to greater than the

positive expected error (i.e. +1.0% for the A version). For fast response, setting the trip point to >10% of the

internal VREF should suffice.

For minimal voltage drop or difference from Vin to the ref pin, it is recommended to use an input resistor <10kΩ

to provide Iref.

TL431, TL432

SLVS543S – AUGUST 2004 – REVISED MAY 2024

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