Datasheet

ADP220/ADP221 Data Sheet
Rev. H | Page 12 of 20
APPLICATIONS INFORMATION
CAPACITOR SELECTION
Output Capacitor
The ADP220/ADP221 are designed for operation with small,
space-saving ceramic capacitors, but the parts function with
most commonly used capacitors as long as care is taken with
regards to the effective series resistance (ESR) value. The ESR
of the output capacitor affects stability of the LDO control loop.
A minimum of 0.70 µF capacitance with an ESR of 1 Ω or less
is recommended to ensure stability of the ADP220/ADP221.
Transient response to changes in load current is also affected by
output capacitance. Using a larger value of output capacitance
improves the transient response of the ADP220/ADP221 to large
changes in the load current. Figure 29 and Figure 30 show the
transient responses for output capacitance values of 1 µF and
4.7 µF, respectively.
2
1
3
CH1 200mA Ω
B
W
CH2 50.0mV
B
W
CH3 10.0mV
B
W
M200ns A CH1 132mA
T 26.60%
T
I
LOAD1
= 1mA TO 200mA, I
LOAD2
= 1mA
I
LOAD1
V
OUT1
V
OUT2,
C
OUT
= 1µF
07572-029
Figure 29. Output Transient Response
I
LOAD1
= 1 mA to 200 mA, I
LOAD2
= 1 mA
CH1 = I
LOAD1
, CH2 = V
OUT1
, CH3 = V
OUT2
, C
OUT
= 1 µF
2
1
3
CH1 200mA Ω
B
W
CH2 50.0mV
B
W
CH3 10.0mV
B
W
M1.00µs A CH1 132mA
T 11.40%
T
I
LOAD1
= 1mA TO 200mA, I
LOAD2
= 1mA
I
LOAD1
V
OUT1
V
OUT2,
C
OUT
= 4.7µF
07572-030
Figure 30. Output Transient Response
I
LOAD1
= 1 mA to 200 mA, I
LOAD2
= 1 mA
CH1 = I
LOAD1
, CH2 = V
OUT1
, CH3 = V
OUT2
, C
OUT
= 4.7 µF
Input Bypass Capacitor
Connecting a 1 µF capacitor from VIN to GND reduces the
circuit sensitivity to the PCB layout, especially when long input
traces or high source impedance are encountered. If an output
capacitance greater than 1 µF is required, the input capacitor
should be increased to match it.
Input and Output Capacitor Properties
Any good quality ceramic capacitor can be used with the ADP220/
ADP221, as long as the capacitor meets the minimum capacit-
ance and maximum ESR requirements. Ceramic capacitors are
manufactured with a variety of dielectrics, each with a different
behavior over temperature and applied voltage. Capacitors must
have an adequate dielectric to ensure the minimum capacitance
over the necessary temperature range and dc bias conditions.
X5R or X7R dielectrics with a voltage rating of 6.3 V or 10 V are
recommended. Y5V and Z5U dielectrics are not recommended,
due to their poor temperature and dc bias characteristics.
Figure 31 depicts the capacitance vs. voltage bias characteristic
of an 0402 1 µF, 10 V, X5R capacitor. The voltage stability of a
capacitor is strongly influenced by the capacitor size and voltage
rating. In general, a capacitor in a larger package or higher voltage
rating exhibits better stability. The temperature variation of the
X5R dielectric is about ±15% over the −40°C to +85°C tempera-
ture range and is not a function of the package or voltage rating.
1.2
1.0
0.8
0.6
0.4
0.2
0
0 2 4 6 8 10
VOLTAGE (V)
CAPACITANCE (µF)
07572-031
Figure 31. Capacitance vs. Voltage Bias Characteristic