ADP1715/ADP1716

Rev. 0 | Page 12 of 20

APPLICATION INFORMATION

CAPACITOR SELECTION

Output Capacitor

The ADP1715/ADP1716 are designed for operation with small,

space-saving ceramic capacitors, but they will function with most

commonly used capacitors as long as care is taken about the

effective series resistance (ESR) value. The ESR of the output

capacitor affects stability of the LDO control loop. A minimum of

2.2 μF capacitance with an ESR of 500 mΩ or less is recommended

to ensure stability of the ADP1715/ADP1716. 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 ADP1715/ADP1716 to large changes in load

current. Figure 32 and Figure 33 show the transient responses for

output capacitance values of 2.2 μF and 22 μF.

2

1

SWITCH SIGNAL TO CHANGE

OUTPUT LOAD FROM 25mA TO 475mA

TIME (2µs/DIV)

Figure 32. Output Transient Response

2

1

SWITCH SIGNAL TO CHANGE

OUTPUT LOAD FROM 25mA TO 475mA

TIME (2µs/DIV)

Figure 33. Output Transient Response

Input Bypass Capacitor

Connecting a 2.2 μF capacitor from the IN pin to GND reduces

the circuit sensitivity to printed circuit board (PCB) layout,

especially when long input traces, or high source impedance, is

encountered. If greater than 2.2 μF of output capacitance is

required, the input capacitor should be increased to match it.

Input and Output Capacitor Properties

Any good quality ceramic capacitors can be used with the

ADP1715/ADP1716, 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.

CURRENT LIMIT AND THERMAL OVERLOAD

PROTECTION

The ADP1715/ADP1716 are protected against damage due to

excessive power dissipation by current and thermal overload

protection circuits. The ADP1715/ADP1716 are designed to

current limit when the output load reaches 750 mA (typical).

When the output load exceeds 750 mA, 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, the output is turned on again and output current is

restored to its nominal value.

Consider the case where a hard short from OUT to ground

occurs. At first the ADP1715/ADP1716 will current limit, so

that only 750 mA is conducted into the short. If self heating of

the junction is great enough to cause its temperature to rise

above 150°C, thermal shutdown will activate, turning off the

output and reducing the output current to zero. As the

junction temperature cools and drops below 135°C, the output

turns on and conducts 750 mA into the short, again causing

the junction temperature to rise above 150°C. This thermal

oscillation between 135°C and 150°C causes a current

oscillation between 750 mA and 0 mA that continues as long

as the short remains at the output.

Current and thermal limit protections are intended to protect

the device against accidental overload conditions. For reliable

operation, device power dissipation should be externally limited

so junction temperatures do not exceed 125°C.

THERMAL CONSIDERATIONS

To guarantee reliable operation, the junction temperature of the

ADP1715/ADP1716 should not exceed 125°C. To ensure the

junction temperature stays below this maximum value, the user