R1121N Datasheet, PDF (15/16 Pages) RICOH electronics devices division – LOW NOISE 150mA LDO REGULATOR

s TECHNICAL NOTES
When using these ICs, be sure to consider following points:

In these ICs, phase compensation is made for securing stable operation even if the load current is varied. For this purpose,
be sure to use a capacitor COUT with good frequency characteristics
and ESR (Equivalent Series Resistance) of which is in the range
described as follows:
4 CE Vout 1
Ceramic
R1121N301B _Capacitor
3 _Vin
GND
2
Vin
Ceramic Capacitor
1µF
ESR
Iout
Spectrum
S.A. _Analyzer
Measuring Circuit for white noise ; R1121N301B
The relations between IOUT (Output Current) and ESR of Output Capacitor are shown below. The conditions when the white
noise level is under 40µV (Avg.) are marked as the hatched area in the graph.
(note: When the additional ceramic capacitors are connected to the Output Pin with Output capacitor for phase compensation,
the operation might be unstable. Because of this, test these ICs with as same external components as ones to be used on the
PCB.)
<measuring conditions>
(1) VIN = 4V
(2) Frequency band :10Hz to 1MHz
(3) Temperature : 25°C
100.0
R1121N301B
Ceramic 1.0µF
100.0
R1121N301B
Ceramic 2.2µF
10.0
10.0
1.0
1.0
0.1
0
50
100
150
Output Current IOUT (mA)
0.1
0
50
100
150
Output Current IOUT (mA)

Make VDD and GND line sufficient. When the impedance of these is high, there is a case to pick up the noise or not to
work correctly.

Connect the capacitor with a capacitance of 1µF or more between VDD and GND as close as possible.

Set external components, especially Output Capacitor, as close as possible to the ICs and make wiring shortest.
Rev.1.11
- 15 -