TL431BQLP datasheet(26/85 Pages) TI2

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9.2.2 Shunt Regulator/Reference

REF

CATHODE

ANODE

VSUP

RSUP

(

Vref

0.1%

TL431

= 1 +

Vref

)

Figure 9-3. Shunt Regulator Schematic

9.2.2.1 Design Requirements

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

Table 9-2. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Reference Initial Accuracy

1.0 %

Supply Voltage

24V

Cathode Current (Ik)

5mA

Output Voltage Level

2.5V- 36V

Load Capacitance

10μF

Feedback Resistor Values and Accuracy (R1 & R2)

10kΩ

9.2.2.2 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

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 9-3, 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 9-3. 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.

TL431, TL432

SLVS543S – AUGUST 2004 – REVISED MAY 2024

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