TS431

Taiwan Semiconductor

Document Number: DS_P0000235

4

Version: H15

ADDITIONAL INFORMATION – STABILITY

optional stability:

A)

No load capacitance across the device, decouple at the load.

B)

Large capacitance across the device, optional decoupling at the load.

The reason for this is that TS431/431A/431B exhibits instability with capacitances in the range of 10nF to 1uF (approx.) at light

cathode current up to 3mA (typ). The device is less stable the lower the cathode voltage has been set for. Therefore while the

device will be perfectly stable operating at a cathode current of 10mA (approx.) with a 0.1uF capacitor across it, it will oscillate

transiently during start up as the cathode current passes through the instability region. Select a very low capacitance, or

alternatively a high capacitance (10uF) will avoid this issue altogether. Since the user will probably wish to have local

decoupling at the load anyway, the most cost effective method is to use no capacitance at all directly across the device. PCB

trace/via resistance and inductance prevent the local load decoupling from causing the oscillation during the transient start up

phase.

Note: if the TS431/431A/431B is located right at the load, so the load decoupling capacitor is directly across it, then this

capacitor will have to be ≤1nF or ≥10uF.

APPLICATIONS EXAMPLES

Figure 1. Voltage Monitor

Figure 2. Output Control for Three Terminal Fixed

Regulator