LTC1798 Series

6

1798fc

Figure 1. Reference Output Load Transient Response, 1µF Output Capacitor

10ms/DIV

100mV/DIV

1mA

0mA

1798 F01a

Longer Battery Life

Series references have an advantage over shunt style

references. To operate, shunt references require a resistor

between the power supply and the output. This resistor

must be chosen to supply the maximum current that is

demanded by the circuit being regulated. When the circuit

being controlled is not operating at this maximum current,

theshuntreferencemustalwayssinkthiscurrent,resulting

in high power dissipation and short battery life.

The LTC1798 series low dropout references do not require

a current setting resistor and can operate with any supply

circuitry being regulated does not demand current, the

LTC1798 series reduces its dissipation and battery life is

extended. If the reference is not delivering load current it

BLOCK DIAGRAM

–

+

IN

6

1798 BD

2

4

OUT

3 (LTC1798)

FB

2.385V

GND

R1

R2

NOTE: R1 AND R2 ARE NOT CONNECTED FOR LTC1798

0.5ms/DIV

100mV/DIV

1mA

0mA

1798 F01b

APPLICATIONS INFORMATION

dissipates only 10.8µW when operating on a 2.7V supply

for LTC1798-2.5, yet the same connection can deliver

10mA of load current when demanded.

Output Bypass Capacitor

TheLTC1798seriesisdesignedtobestablewithorwithout

capacitive loads. With no capacitive load, the reference

is ideal for fast settling applications, or where PC board

space is at a premium.

In applications with significant output loading changes, an

outputbypasscapacitorofupto1µFcanbeusedtoimprove

theoutputtransientresponse.Figure1showstheresponse

ofthereferencetoa1mAto0µAloadstepwitha1µFoutput

capacitor.Ifmorethan1µFofoutputcapacitanceisrequired,

a resistor in series with the capacitor is recommended