TL431ACLPRE3 datasheet(22/82 Pages) TI1

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TL431, TL431A, TL431B

TL432, TL432A, TL432B

SLVS543O – AUGUST 2004 – REVISED JANUARY 2015

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Typical Applications (continued)

10.2.1.1 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 5 V

Input Resistance

10 k

Supply Voltage

24 V

Cathode Current (Ik)

5 mA

Output Voltage Level

~2 V – VSUP

Logic Input Thresholds VIH/VIL

10.2.1.2 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

10.2.1.2.1

Basic Operation

In the configuration shown in Figure 25 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 26, where the RSUP=10 kΩ (IKA=500 µA)

situation responds much slower than RSUP=1 kΩ (IKA=5 mA). With the TL43xx's max Operating Current (IMIN)

being 1 mA, operation below that could result in low gain, leading to a slow response.

10.2.1.2.1.1

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 2.5 V ±(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 <10k

to provide Iref.

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