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LTC1550L

Low Noise, Switched Capacitor Regulated Voltage Inverters

Linear Technology 

LTC1550L/LTC1551L

APPLICATIONS INFORMATION

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 2.2µF surface mount ceramic capacitor at VCC generally

provides adequate output ripple performance for most

applications.

8

VCC = 5V

7 TA = 25°C

COUT = 10µF

6

5

4

3

2

1

0

0.1

1

10

100

INPUT CAPACITANCE (µF)

1550L/51L F08

Figure 7. Output Ripple vs Input Bypass Capacitance

TYPICAL APPLICATION

– 4.1V Output GaAs FET Bias Generator

4.5V ≤ VCC ≤ 5.25V

+ CIN

2.2µF

1

SHDN

2

VCC

8

REG

7

CPOUT

LTC1550L-4.1

3 C1+

GND 6

4

VOUT

C1– 5

CCP

0.1µF

– 4.1V BIAS

C1

0.1µF

COUT

10µF

CL

0.1µF

GaAs

TRANSMITTER

1550L/51L TA02

10

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