AP7333

300mA, Low Quiescent Current, Fast Transient

Low Dropout Linear Regulator

AP7333 Rev. 2

9 of 12

NOVEMBER 2009

www.diodes.com

Application Note

Input Capacitor

A 1

μF ceramic capacitor is recommended to connect between

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.

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 1

μF to 4.7μF, Equivalent Series Resistance (ESR) is from

10m

Ω 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.