L432V データシートの表示（PDF） - Niko Semiconductor

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L432V

1.24V Low-Voltage Adjustable Precision Shunt Regulator

Niko Semiconductor 

NIKO-SEM

1.24V Low-Voltage Adjustable

Precision Shunt Regulator

TEST CIRCUITS

VIN

VKA VIN

VKA VIN

I REF

IK

R1 I REF

IK

V REF

R2

L432

VKA

I K (OFF)

- TEST CIRCUIT 1 -

(VKA = VREF)

- TEST CIRCUIT 2 -

(VKA > VREF)

- TEST CIRCUIT 3 -

(OFF STATE CURRENT)

Applications Information – Stability

Selection of load capacitance when using

L432 as a shunt regulator

When the L432 is used as a shunt regulator,

two options for selection of CL are

recommended for optimal stability:

1. No load capacitance across the device,

decouple at the load.

2. Large capacitance across the device,

optional decoupling at the load.

The reason for this is that L432 exhibits

instability with capacitances in the range of

1nF to 1uf (approx.) at light cathode currents

(up to 3mA typical). 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

with a 0.1uF capacitor across it, it will oscillate

transiently during start-up as the cathode

current passes through the instability region.

Selecting a very low

(or preferably, no)capacitance, or alter-

natively a high capacitance (such as 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 de-

coupling from causing the oscillation during

the transient start-up phase. Note : if the

L432 is located right at the load, so the

load decoupling capacitor is directly across

it, then this capacitor will have to be

≦ 100pF or ≧ 1uF.

3

NOV-21-2001

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