TL431BQLPM datasheet(24/82 Pages) TI1

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REF

CATHODE

ANODE

VSUP

RSUP

(

Vref

0.1%

TL431

= 1 +

Vref

)

TL431, TL431A, TL431B

TL432, TL432A, TL432B

SLVS543O – AUGUST 2004 – REVISED JANUARY 2015

www.ti.com

10.2.2 Shunt Regulator/Reference

Figure 27. Shunt Regulator Schematic

10.2.2.1 Design Requirements

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

Table 2. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Reference Initial Accuracy

1.0 %

Supply Voltage

24 V

Cathode Current (Ik)

5 mA

Output Voltage Level

2.5 V - 36 V

Load Capacitance

100 nF

Feedback Resistor Values and Accuracy (R1 & R2)

10 k

10.2.2.2 Detailed Design Procedure

When using TL431 as a Shunt Regulator, determine the following:

•

Input Voltage Range

•

Temperature Range

•

Total Accuracy

•

Cathode Current

•

Reference Initial Accuracy

•

Output Capacitance

10.2.2.2.1

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 27, with R1 & R2

being the resistive bridge. The cathode/output voltage in the shunt regulator configuration can be approximated

by the equation shown in Figure 27. The cathode voltage can be more accuratel determined by taking in to

account the cathode current:

Vo=(1+R1/R2)*VREF-IREF*R1

In order for this equation to be valid, TL43xx 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, TL431C,

TL432C.

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