3A Ultra Low Dropout Linear Regulator

TJ4230

Apr. 2011 – Rev. 1. 0

6/9

HTC

APPLICATION INFORMATION

Introduction

TJ4230 is intended for applications where high current capability and very low dropout voltage are required. It

provides a simple, low cost solution that occupies very little PCB estate. Additional features include an enable

pin to allow for a very low power consumption standby mode, an adjustable pin to provide a fully adjustable

output voltage, and SENSE pin to provide better remote load regulation characteristics.

Component Selection

Input Capacitor :

A large bulk capacitance over than 10uF should be closely placed to the input supply pin of the TJ4230 to

ensure that the input supply voltage does not sag. Also a minimum of 10uF ceramic capacitor is

bulk capacitor on the rail. Additionally, input droop due to load transients is reduced, improving load transient

response. Additional capacitance may be added if required by the application.(See Fig.1)

Output Capacitor :

A minimum ceramic capacitor over than 10uF should be very closely placed to the output voltage pin of the

TJ4230. Increasing capacitance will improve the overall transient response and stability.

Decoupling (Bypass) Capacitor :

In very electrically noisy environments, it is recommended that additional ceramic capacitors be placed from

VIN to GND. The use of multiple lower value ceramic capacitors in parallel with output capacitor also allows to

achieve better transient performance and stability if required by the application.(See Fig.1)

Feed-Forward Capacitor

To get the higher PSRR than the inherent performance of TJ4230, it is recommended that additional ceramic

feed-forward capacitor be placed from VOUT pin to ADJ pin. The capacitance of feed-forward capacitor with

range of 10pF to 1uF allows to achieve better PSRR performance when required by the application.(See

Fig.2)

Fig. 1. Application with Decoupling Capacitor,

Fig. 2. Application with Feed-Forward Capacitor,

CC1 & CC2

CFF

Delayed Start-Up

When power sequence control is required or rising time of input supply voltage is over than 100usec, it is

recommended to apply delayed start-up by using Cdelay as shown in Fig. 3. It can adjust proper delay by

Rp-Cdelay time constant. And also it can prevent any unexpected transient characteristics at output voltage

when the rising time of input supply voltage is as long as 100usec or longer.

Fig. 3. Application with Delayed Start-Up

10uF

EN

SENSE

TJ4230

GND

VIN

VOUT

CC2

10uF

CC1

10uF

10uF

EN

ADJ

TJ4230

GND

VIN

VOUT

R2

R1

CC2

CFF

CC1

10uF

10uF

EN

ADJ

TJ4230

GND

VIN

VOUT

R2

R1

CFF