参数资料
型号: ADP122-3.3-EVALZ
厂商: Analog Devices Inc
文件页数: 12/24页
文件大小: 0K
描述: BOARD EVALUATION 3.3V ADP122
标准包装: 1
每 IC 通道数: 1 - 单
输出电压: 3.3V
电流 - 输出: 300mA
输入电压: 2.3 ~ 5.5 V
稳压器类型: 正,固定式
工作温度: -40°C ~ 85°C
板类型: 完全填充
已供物品:
已用 IC / 零件: ADP122

ADP122/ADP123
APPLICATIONS INFORMATION
CAPACITOR SELECTION
Output Capacitor
The ADP122/ADP123 are designed for operation with small,
space-saving ceramic capacitors, but these devices can function
with most commonly used capacitors as long as care is taken to
ensure an appropriate effective series resistance (ESR) value. The
ESR of the output capacitor affects the stability of the LDO control
loop. A minimum of 0.70 μF capacitance with an ESR of 1 ? or
less is recommended to ensure stability of the ADP122/ADP123.
The transient response to changes in load current is also affected by
the output capacitance. Using a larger value of output capacitance
improves the transient response of the ADP122/ADP123 to
dynamic changes in load current. Figure 32 and Figure 33 show
the transient responses for output capacitance values of 1 μF and
4.7 μF, respectively.
I OUT
1mA TO 300mA LOAD STEP
1
Data Sheet
Input and Output Capacitor Properties
Any good quality ceramic capacitors can be used with the ADP122/
ADP123, as long as the capacitor meets the minimum capacitance
and maximum ESR requirements. Ceramic capacitors are manu-
factured with a variety of dielectrics, each with 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. Using an
X5R or X7R dielectric with a voltage rating of 6.3 V or 10 V is
recommended. However, using Y5V and Z5U dielectrics is not
recommended for any LDO, due to their poor temperature and
dc bias characteristics.
Figure 34 depicts the capacitance vs. capacitor voltage bias charac-
teristics of a 0603, 1 μF, 6.3 V X5R capacitor. The voltage stability of
a capacitor is strongly influenced by the capacitor size and the
voltage rating. In general, a capacitor in a larger package or of a
higher voltage rating exhibits better stability. The temperature
variation of the X5R dielectric is about ±15% over the ?40°C to
+85°C temperature range and is not a function of package or
voltage rating.
1.10
1.05
2
V OUT
V IN = 3.7V
1.00
0.95
V OUT = 3.3V
0.90
CH1 200mA
? B
W
CH2 50.0mV
B
W
M 400ns A CH1
196mA
0.85
T
14.80%
Figure 32. Output Transient Response, C OUT = 1 μF
I OUT
0.80
0.75
0.70
1mA TO 300mA LOAD STEP
0
1
2
3
4
5
6
7
1
2
BIAS VOLTAGE (V)
Figure 34. Capacitance vs. Capacitor Voltage Bias Characteristics
Equation 1 can be used to determine the worst-case capacitance,
accounting for capacitor variation over temperature, component
tolerance, and voltage.
C EFF = C × (1 ? TEMPCO ) × (1 ? TOL )
(1)
V OUT
where:
CH1 200mA ?
B
W
CH2 20.0mV
M 400ns A CH1 196mA
T 15.00%
V IN = 3.7V
V OUT = 3.3V
C EFF is the effective capacitance at the operating voltage.
TEMPCO is the worst-case capacitor temperature coefficient.
TOL is the worst-case component tolerance.
Figure 33. Output Transient Response, C OUT = 4.7 μF
Input Bypass Capacitor
Connecting a 1 μF capacitor from VIN to GND reduces the circuit
sensitivity to the printed circuit board (PCB) layout, especially
when a long input trace or high source impedance is encountered.
If greater than 1 μF of output capacitance is required, the input
capacitor should be increased to match it.
In this example, the worst-case temperature coefficient (TEMPCO)
over ?40°C to +85°C is assumed to be 15% for an X5R dielectric.
The tolerance of the capacitor (TOL) is assumed to be 10%, and
C is 0.96 μF at 4.2 V from the graph in Figure 34.
Substituting these values in Equation 1 yields
C EFF = 0.96 μF × (1 ? 0.15) × (1 ? 0.1) = 0.734 μF
Rev. E | Page 12 of 24
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