LTC1144 查看數據表（PDF） - Linear Technology
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LTC1144 Datasheet PDF : 12 Pages
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LTC1144
Test Circuit
C1 +
10µF
1
8
2
7
3 LTC1144 6
4
5
COSC
V+
15V
IS
EXTERNAL
OSCILLATOR RL IL
VOUT
C2
10µF
Figure 1.
1144 F01
Applications Information
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)
REQUIV = 1/(f × C1). Thus, the equivalent circuit for the
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
REQUIV
V1
V2
V1
V2
f
RL
C1
C2
1144 F02
C2 RL
REQUIV
=
f
1
× C1
1144 F03
Figure 3. Switched-Capacitor Equivalent Circuit
Figure 2. Switched-Capacitor Building Block
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
REQUIV
BOOST
10X
(1)
OSC
OSC
(7)
SHDN
(6)
V+
(8)
φ
÷2
φ
SW1
SW2
CAP+
(2)
+
C1
CAP–
(4)
GND
(3)
VOUT
(5)
+ C2
1144 F04
A new variable REQUIV has been defined such that
Figure 4. LTC1144 Switched-Capacitor
Voltage Converter Block Diagram
1144fa
6
For more information www.linear.com/LTC1144
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