ADP1707 Analog Devices, ADP1707 Datasheet - Page 12

• Manufacturer Part Number: ADP1707
• Description: 1 A, Low Dropout, CMOS Linear Regulator with Tracking
• Manufacturer: Analog Devices

ADP1706/ADP1707/ADP1708
APPLICATION 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.
V
FROM 50mA TO 950mA
V
FROM 50mA TO 950mA
Figure 33. Output Transient Response, C
Figure 34. Output Transient Response, C
OUT
OUT
RESPONSE TO LOAD STEP
RESPONSE TO LOAD STEP
TIME (2μs/DIV)
TIME (2μs/DIV)
OUT
OUT
V
V
C
C
V
V
C
C
IN
OUT
IN
OUT
= 4.7 μF
IN
OUT
IN
OUT
= 22 μF
= 3.8V
= 4.7μF
= 3.8V
= 22μF
= 1.6V
= 4.7μF
= 1.6V
= 22μF
Rev. 0 | Page 12 of 20
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 dielec-
trics, 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
Figure 35 shows an application where the ADP1707 tracking
feature is used. An ADP1706 powers the I/O of a microproces-
sor 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 I/O.
CURRENT LIMIT AND THERMAL OVERLOAD
PROTECTION
The ADP1706/ADP1707/ADP1708 are protected against
damage due to excessive power dissipation by current and
thermal overload protection circuits. The ADP1706/ADP1707/
ADP1708 are designed to reach current limit when the output
load reaches 1.5 A (typical). When the output load exceeds
1.5 A, the output voltage is reduced to maintain a constant
current limit.
5V
ADP1706-2.5
RATIO VOLTAGE TRACKING
IN
EN
SS
Figure 35. Voltage Tracking Feature Using ADP1707
GND
OUT
R1
R2
ADP1707-1.2
TRK
IN
EN
GND
2.5V
OUT
V
1.2V
2.5V
1.2V
OUT
I/O POWER RAIL
TIME
CORE RAIL
RATIO
TRACKING