REF

CATHODE

ANODE

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R2

R1

(

R1

0.1%

R2

0.1%

ATL43xLIx

= 1 +

)

17

ATL431LI

ATL432LI

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SLVSDU6D – JULY 2017 – REVISED NOVEMBER 2019

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11.2.3 Shunt Regulator/Reference

Figure 26. Shunt Regulator Schematic

11.2.3.1 Design Requirements

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

Table 3. 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

2 µF

Feedback Resistor Values and Accuracy (R1 and R2)

10 kΩ

11.2.3.2 Detailed Design Procedure

When using ATL431LI as a Shunt Regulator, determine the following:

•

Input Voltage Range

•

Temperature Range

•

Total Accuracy

•

Cathode Current

•

Reference Initial Accuracy

•

Output Capacitance

11.2.3.2.1

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 26, with R1 and

R2 being the resistive bridge. The cathode/output voltage in the shunt regulator configuration can be

approximated by the equation shown in Figure 26. The cathode voltage can be more accuratel determined by

taking in to account the cathode current:

(1)

In order for this equation to be valid, ATL431LI 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 Specifications.