Data Sheet

ADP1706/ADP1707/ADP1708

APPLICATIONS INFORMATION

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Rev. B | 14 of 19

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.

Figure 33. Output Transient Response, COUT = 4.7 µF

Figure 34. Output Transient Response, COUT = 22 µF

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

Figure 35. Voltage Tracking Feature Using the ADP1707

Figure 35 shows an application where the ADP1707 tracking fea-

ture is used. An ADP1706 powers the input/output of a microproc-

essor 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.

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.

Thermal overload protection is included, which limits the junction

temperature to a maximum of 150°C (typical). Under extreme

conditions (that is, high ambient temperature and power dissipation)

when the junction temperature starts to rise above 150°C, the

output is turned off, reducing the output current to zero. When

the junction temperature drops below 135°C (typical), the output is

turned on again and output current is restored to its nominal value.