LTC1144

6

1144fa

For more information www.linear.com/LTC1144

TesT circuiT

applicaTions inForMaTion

1

2

3

4

8

7

6

5

+

C1

10µF

C2

10µF

15V

EXTERNAL

OSCILLATOR

1144 F01

LTC1144

Figure 1.

Figure 2. Switched-Capacitor Building Block

Figure 3. Switched-Capacitor Equivalent Circuit

Figure 4. LTC1144 Switched-Capacitor

Voltage Converter Block Diagram

Theory of Operation

To understand the theory of operation of the LTC1144,

a review of a basic switched-capacitor building block is

helpful.

In Figure 2, when the switch is in the left position, capaci-

tor C1 will charge to voltage V1. The total charge on C1

will be q1 = C1V1. The switch then moves to the right,

discharging C1 to voltage V2. After this discharge time,

the charge on C1 is q2 = C1V2. Note that charge has been

transferred from the source V1 to the output V2. The

amount of charge transferred is:

∆q = q1 – q2 = C1(V1 – V2)

If the switch is cycled f times per second, the charge

transfer per unit time (i.e., current) is:

I = f

× ∆q = f × C1(V1 – V2)

Rewriting in terms of voltage and impedance equivalence,

I

=

V1

− V2

1

f

×C1









=

V1

− V2

V2

C2

C1

V1

f

1144 F02

V2

C2

V1

1144 F03

1

f

× C1

switched-capacitor network is as shown in Figure 3.

Examination of Figure 4 shows that the LTC1144 has the

same switching action as the basic switched-capacitor

building block. With the addition of finite switch on-

resistance and output voltage ripple, the simple theory,

although not exact, provides an intuitive feel for how the

device works.

For example, if you examine power conversion efficiency

as a function of frequency (see Figure 5), this simple

SHDN

(6)

OSC

(7)

10X

(1)

BOOST

1144 F04

OSC

(8)

SW1

SW2

(2)

(4)

GND

(3)

(5)

C2

C1

+

+

φ

φ