ADP1706ACPZ-1.3-R7(RevA) View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
ADP1706ACPZ-1.3-R7 Datasheet PDF : 20 Pages
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ADP1706/ADP1707/ADP1708
APPLICATIONS INFORMATION
CAPACITOR SELECTION
Output Capacitor
The ADP1706/ADP1707/ADP1708 are designed for
operation with small, space-saving ceramic capacitors, but
they function with most commonly used capacitors as long as
care is taken with the effective series resistance (ESR) value.
The ESR of the output capacitor affects stability of the LDO
control loop. A minimum of 4.7 μF capacitance with an ESR
of 500 mΩ or less is recommended to ensure stability of the
ADP1706/ADP1707/ADP1708. 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 ADP1706/ADP1707/ADP1708 to
large changes in load current. Figure 33 and Figure 34 show
the transient responses for output capacitance values of 4.7 μF
and 22 μF, respectively.
VOUT RESPONSE TO LOAD STEP
FROM 50mA TO 950mA
VIN = 3.8V
VOUT = 1.6V
CIN = 4.7μF
COUT = 4.7μF
TIME (2μs/DIV)
Figure 33. Output Transient Response, COUT = 4.7 μF
VOUT RESPONSE TO LOAD STEP
FROM 50mA TO 950mA
VIN = 3.8V
VOUT = 1.6V
CIN = 22μF
COUT = 22μF
TIME (2μs/DIV)
Figure 34. Output Transient Response, COUT = 22 μF
Data Sheet
Input Bypass Capacitor
Connecting a 4.7 μF capacitor from the IN pin to GND reduces
the circuit sensitivity to the printed circuit board (PCB) layout,
especially when long input traces, or high source impedance,
is encountered. If greater than 4.7 μF of output capacitance is
required, it is recommended that the input capacitor be increased
to match it.
Input and Output Capacitor Properties
Any good quality ceramic capacitors can be used with the
ADP1706/ADP1707/ADP1708, as long as they meet the minimum
capacitance and maximum ESR requirements. Ceramic capacitors
are manufactured with a variety of dielectrics, each with different
behavior over temperature and applied voltage. Capacitors must
have a dielectric adequate 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.
VOLTAGE TRACKING APPLICATIONS
RATIO VOLTAGE TRACKING
ADP1706-2.5
IN OUT
5V
EN
2.5V
SS
GND
R1
2.5V
VOUT
R2
1.2V
ADP1707-1.2
1.2V
OUT
TRK
IN
EN
GND
I/O POWER RAIL
RATIO
TRACKING
CORE RAIL
TIME
Figure 35. Voltage Tracking Feature Using the ADP1707
Figure 35 shows an application where the ADP1707 tracking
feature is used. An ADP1706 powers the input/output of a
microprocessor and an ADP1707 powers the core. At startup,
the output of the ADP1706 ramps to 2.5 V, which is divided
down via a voltage divider (R1 and R2) to a lower voltage at the
TRK pin of the ADP1707. The output of the ADP1707 thus follows
the TRK pin and ramps up steadily to 1.2 V. This implementation
ensures that the core of the processor powers up after the input/
output.
Rev. A | Page 14 of 20
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