Datasheet

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
V
OUT
V
IN
= 5V
V
OUT
= 3.3V
C
IN
= 2.2µF
C
OUT
= 2.2µF
06110-045
TIME (2µs/DIV)
2V/DI
V
20mV/DI
V
Figure 32. Output Transient Response
2
1
SWITCH SIGNAL TO CHANGE
OUTPUT LOAD FROM 25mA TO 475mA
V
OUT
V
IN
= 5V
V
OUT
= 3.3V
C
IN
= 22µF
C
OUT
= 22µF
06110-046
TIME (2µs/DIV)
2V/DI
V
20mV/DI
V
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