AP7335A View Datasheet(PDF) - Diodes Incorporated.

Part Name

Description

Manufacturer

AP7335A

300mA, LOW QUIESCENT CURRENT, FAST TRANSIENT LOW DROPOUT LINEAR REGULATOR

Diodes Incorporated. 

AP7335A

300mA, LOW QUIESCENT CURRENT, FAST TRANSIENT

LOW DROPOUT LINEAR REGULATOR

Application Note

Input Capacitor

A 1μF ceramic capacitor is recommended between 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 reduce

noise. For PCB layout, a wide copper trace is required for

both IN and GND pins. A lower ESR capacitor type allows

the use of less capacitance, while higher ESR type

requires more capacitance.

Output Capacitor

The output capacitor is required to stabilize and improve

the transient response of the LDO. The AP7335A is stable

with very small ceramic output capacitors. Using a ceramic

capacitor value that is at least 1μF with ESR > 15mΩ on

the output ensures stability. Higher capacitance values

help to improve line and load transient response. The

output capacitance may be increased to keep low

undershoot and overshoot. Output capacitor must be

placed as close as possible to OUT and GND pins.

Region of Stable COUT ESR vs. Load Current

100

Unstable Range

10

1

stable Range

0.1

VIN=5.5V

CIN=COUT=1μF

0.01

0.001

0

Unstable Range

50 100 150 200 250 300

Load Current (mA)

No Load Stability

No minimum load is required to keep the device stable.

The device will remain stable and regulated in no load

condition.

ON/OFF Input Operation

The AP7335A is turned on by setting the EN pin high, and

is turned off by pulling it low. If this feature is not used, the

EN pin should be tied to IN pin to keep the regulator

output on at all time. To ensure proper operation, the

signal source used to drive the EN pin must be able to

swing above and below the specified turn-on/off voltage

thresholds listed in the Electrical Characteristics section

under VIL and VIH.

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

650mA 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, short circuit

protection will be triggered and clamp the output current

to approximately 160mA. 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 +145°C, allowing the

device to cool down. When the junction temperature

reduces to approximately +130°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 enabled, the AP7335A is able to provide full power

in as little as tens of microseconds, typically 220µs,

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 LDO can 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 LDO.

The AP7335A’s fast transient response from 0 to 300mA

provides stable voltage supply for fast DSP and GSM

chipset with fast changing load.

Low Quiescent Current

The AP7335A, consuming only around 35µA for all input

range, provides great power saving in portable and low

power applications.

AP7335A

Document number: DS35267 Rev. 2 - 2

7 of 12

www.diodes.com

July 2011

© Diodes Incorporated

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