TLV431ACLP datasheet(23/54 Pages) TI

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8.2.2 Shunt Regulator/Reference

Figure 8-5. Shunt Regulator Schematic

8.2.2.1 Design Requirements

For this design example, use the parameters listed in Table 8-2 as the input parameters.

Table 8-2. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Reference Initial Accuracy

1.0%

Supply Voltage

Cathode Current (Ik)

1mA

Output Voltage Level

1.24V - 6V

Load Capacitance

100pF

Feedback Resistor Values and Accuracy (R1 and R2)

10kΩ

8.2.2.2 Detailed Design Procedure

When using TLV431 as a Shunt Regulator, determine the following:

• Input voltage range

• Temperature range

• Total accuracy

• Cathode current

• Reference initial accuracy

• Output capacitance

8.2.2.2.1 Programming Output/Cathode Voltage

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 8-5, 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 8-5. The cathode voltage can be more accurately determined by taking the cathode

current in to account

VO = (1 + R1 / R2) × Vref – Iref × R1 (1)

For Equation 1 to be valid, TLV431 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 Recommended Operating Conditions table.

8.2.2.2.2 Total Accuracy

When programming the output above unity gain (Vka = Vref), TLV431 is susceptible to other errors that may

effect the overall accuracy beyond Vref. These errors include:

• R1 and R2 accuracies

• VI(dev) – Change in reference voltage over temperature

• ΔVref / ΔVKA – Change in reference voltage to the change in cathode voltage

• |zKA| – Dynamic impedance, causing a change in cathode voltage with cathode current

Worst-case cathode voltage can be determined taking all of the variables in to account. Application note Setting

the Shunt Voltage on an Adjustable Shunt Regulator (SLVA445) assists designers in setting the shunt voltage to

achieve optimum accuracy for this device.

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TLV431, TLV431A, TLV431B

SLVS139Z – JULY 1996 – REVISED JUNE 2024

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