LTC1550LIGN datasheet(10/12 Pages) LINER

10 / 12 page

LTC1550L/LTC1551L

APPLICATIONS INFORMATION

Figure 7. Output Ripple vs Input Bypass Capacitance

INPUT CAPACITANCE (

µF)

0.1

100

1550L/51L F08

VCC = 5V

TA = 25°C

COUT = 10µF

Output Ripple vs Input Bypass Capacitor

The input bypass capacitor (CIN) can also have a fairly

significant impact on the output ripple. CIN provides most

of the LTC1550L/LTC1551L’s supply current while it is

charging the flying capacitor (C1). Inadequate input

bypassing can cause the VCC supply to dip when the

charge pump switches, causing the output linear regulator

to momentarily stop regulating. CIN should be mounted as

close to the LTC1550L/LTC1551L VCC and GND pins as

possible and its value should be significantly larger than

C1. Surface mount tantalum or ceramic capacitors with

low ESR generally provide adequate performance. Figure 7

shows the LTC1550L/LTC1551L peak-to-peak output ripple

vs CIN, taken using the test circuit in Figure 3 with ILOAD set

at 5mA. COUT is a 10µF in parallel with a 0.1µF ceramic

capacitor.

A 2.2

µF surface mount ceramic capacitor at VCC generally

provides adequate output ripple performance for most

applications.

4.5V

≤ VCC ≤ 5.25V

REG

CPOUT

SHDN

VCC

C1+

VOUT

LTC1550L-4.1

– 4.1V BIAS

GND

C1–

COUT

µF

1550L/51L TA02

CCP

0.1

µF

GaAs

TRANSMITTER

0.1

µF

CIN

2.2

µF

0.1

µF

– 4.1V Output GaAs FET Bias Generator

TYPICAL APPLICATION

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