AP7333
300mA, Low Quiescent Current, Fast Transient
Low Dropout Linear Regulator
AP7333 Rev. 2 9 of 12 NOVEMBER 2009
www.diodes.com © Diodes Incorporated
Application Note
Input Capacitor
A 1μF ceramic capacitor is recommended to connect between
V
IN
and GND pins to decouple input power supply glitch and
noise. The amount of the capacitance may be increased
without limit. This input capacitor must be located as close as
possible to the device to assure input stability and less noise.
For PCB layout, a wide copper trace is required for both V
IN
and
GND. A lower ESR capacitor allows the use of less
capacitance, while higher ESR type requires more
capacitance.
Output Capacitor
The output capacitor is required to stabilize and help transient
response for LDO. The AP7333 is stable with very small
ceramic output capacitors. The recommended capacitance is
from 1μF to 4.7μF, Equivalent Series Resistance (ESR) is from
10mΩ to 200mΩ, and temperature characteristic is X7R or X5R.
Higher capacitance values help to improve load/line transient
response. The output capacitance may be increased to keep
low undershoot/overshoot. Place output capacitor as close as
possible to OUT and GND pins, and keep the leads as short as
possible.
No Load Stability
No minimum load is required to keep the device stable. The
device will remain stable and regulated in no load condition.
Current Limit Protection
When output current at OUT pin is higher than current limit
threshold, the current limit protection will be triggered and
clamp the output current to approximately 600mA to prevent
over-current and to protect the regulator from damage due to
overheating.
Short Circuit Protection
When OUT pin is short-circuit to GND or OUT pin voltage is
less than 200mV, short circuit protection will be triggered and
clamp the output current to approximately 100mA. This feature
protects the regulator from over-current and damage due to
overheating.
Thermal Shutdown Protection
Thermal protection disables the output when the junction
temperature rises to approximately +140°C, allowing the device
to cool down. When the junction temperature reduces to
approximately +125°C the output circuitry is enabled again.
Depending on power dissipation, thermal resistance, and
ambient temperature, the thermal protection circuit may cycle
on and off. This cycling limits the heat dissipation of the
regulator, protecting it from damage due to overheating.
Ultra Fast Start-up
After turned on, the AP7333 is able to provide full power in as
little as tens of microseconds, typically 80µs, without sacrificing
low ground current. This feature will help load circuitry move in
and out of standby mode in real time, eventually extend battery
life for mobile phones and other portable devices.
Fast Transient Response
Fast transient response LDOs can also extend battery life.
TDMA-based cell phone protocols such as Global System for
Mobile Communications (GSM) have a transmit/receive duty
factor of only 12.5 percent, enabling power savings by putting
much of the baseband circuitry into standby mode in between
transmit cycles. In baseband circuits, the load often transitions
virtually instantaneously from 100µA to 100mA. To meet this
load requirement, the LDO must react very quickly without a
large voltage drop or overshoot — a requirement that cannot
be met with conventional, general-purpose LDOs.
The AP7333’s fast transient response from 0 to 300mA
provides stable voltage supply for fast DSP and GSM chipset
with fast changing load.
Small Overshoot and Undershoot
The AP7333 has small and controlled overshoot and
undershoot in load and line transitions. This helps to protect
supplied circuit from damage and operation error caused by
glitches. This feature also permits the usage of small value
output decoupling capacitor with AP7333.
Low Quiescent Current
The AP7333, consuming only around 65µA for all input range
and output loading, provides great power saving in portable
and low power applications.
Wide Output Options
The AP7333, with multiples of fixed output voltage options,
provides a versatile LDO solution for many portable
applications.
