Datasheet

ADP320
Rev. A | Page 15 of 20
APPLICATIONS INFORMATION
CAPACITOR SELECTION
Output Capacitor
The ADP320 triple LDO is designed for operation with small,
space-saving ceramic capacitors, but the parts function with
most commonly used capacitors as long as care is taken in
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 ADP320 triple LDO.
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 ADP320 triple LDO to
large changes in the load current. Figure 42 show the transient
response for an output capacitance value of 1 µF.
CH1 100mA Ω CH2 50mV
CH4 10mVCH3 10mV
M40µs A CH1 44mA
1
2
3
4
T 9.8%
B
W
B
W
B
W
B
W
09874-042
I
LOAD1
V
OUT1
V
OUT2
V
OUT3
Figure 42. Output Transient Response,
I
LOAD1
= 1 mA to 200 mA, I
LOAD2
= 1 mA, I
LOAD3
= 1 mA,
CH1 = I
LOAD1
, CH2 = V
OUT1
, CH3 = V
OUT2
, CH4 = V
OUT3
Input Bypass Capacitor
Connecting a 1 µF capacitor from VIN1/VIN2, VIN3, and
VBIAS 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 may be used with the ADP320
triple LDO, 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 43 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)
09874-043
Figure 43. Capacitance vs. Voltage Bias Characteristic