2A Ultra Low Dropout Linear Regulator
APPLICATION INFORMATION
Introduction
TJ4220
TJ4220 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/A(Output Load) should be closely placed to the input supply pin of
the TJ4220 to ensure that the input supply voltage does not sag. Also a minimum of 10uF ceramic capacitor is
recommended to be placed directly next to the VIN Pin. It allows for the device being some distance from any
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/A(Output Load) should be very closely placed to the output
voltage pin of the TJ4220. 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 TJ4220, 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,
CC1 & CC2
Fig. 2. Application with Feed-Forward Capacitor,
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
Jun. 2011 – R1.0.6
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HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
