What is the load transient response of an LDO?

Transient Response of an LDO

Load transient response refers to the sequence of behavior in which the output voltage of an LDO temporarily fluctuates and then returns to its nominal voltage when the load current changes suddenly.
For example, if the load current suddenly increases, the LDO output voltage undershoots before returning to the nominal voltage. On the other hand, if the load current suddenly decreases, the LDO output voltage overshoots before returning to the nominal voltage.

Figure 1:Example of an output voltage waveform in response to changes in load current
Figure 1:Example of an output voltage waveform in response to changes in load current

Mechanism of load transient response

An LDO maintains its output voltage using negative feedback. However, the internal feedback circuit has a limited response speed, which causes a time lag before it can react to changes in load current. This time lag results in transient voltage fluctuations when the load current changes rapidly.

Introduction of an LDO with fast load transient response

We have released the TCR5FM series with high-speed load transient response.
The main characteristics are as follows.

Series TCR5FM series
Package Name DFN4D
Size typ. (mm) 1.0×1.0×0.37
Operating ranges Input voltage VIN (V) 1.55~5.5
Output current IOUT (mA) 500
Operation temperature Topr (°C) -40~125
Electrical characteristics
(Unless otherwise specified,
Tj=25°C、VIN= 3.3V、VOUT=2.8V)
Output voltage VOUT (V) 0.9~5.0
Output voltage accuracy
VOUT (%)
IOUT=1~500mA
Tj=-40~125°C
±2.2
Quiescent current
IB(ON) typ. (μA)
IOUT=0mA 10
Stand-by current
IB(OFF) typ. (μA)
VCT=0V 0.1
Drop-out voltage
VDO typ. (mV)
IOUT=500mA 220
Load transient response
⊿VOUT typ. (mV)
IOUT=1mA→500mA, tr=1μs -60
IOUT=500mA→1mA, tf=1μs 40
IOUT=0mA→100mA, tr=1μs -75
IOUT=100mA→0mA, tf =1μs 25
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