LTC1144CS8 Linear Technology, LTC1144CS8 Datasheet - Page 5

• Manufacturer Part Number: LTC1144CS8
• Description: IC VOLT CONV SW-CAP W/SHTDN8SOIC
• Manufacturer: Linear Technology
• Type: Switched Capacitor (Charge Pump), Invertingr

Specifications of LTC1144CS8

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Current - Output: 50mA
• Frequency - Switching: 4kHz ~ 10kHz
• Voltage - Input: 2 ~ 18 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Power - Output: 500mW
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Output: -

If the switch is cycled f times per second, the charge
transfer per unit time (i.e., current) is:
Rewriting in terms of voltage and impedance equivalence,
A new variable R
= 1/(f C1). Thus, the equivalent circuit for the switched-
capacitor network is as shown in Figure 3.
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, capacitor
C1 will charge to voltage V1. The total charge on C1 will be
q1 = C1V1. The switch then moves to the right, discharg-
ing 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:
A
TEST CIRCUITS
PPLICATI
I = f
I
q = q1 – q2 = C1(V1 – V2)
V
f C
1
Figure 2. Switched-Capacitor Building Block
1
q = f C1(V1 – V2)
V
1
2
V1
EQUIV
O
V
R
1
U
EQUIV
S
has been defined such that R
V
C1
f
2
I FOR ATIO
U
10 F
C1
C2
+
R
L
W
V2
1
2
3
4
1144 F02
LTC1144
U
EQUIV
8
7
6
5
Figure 1.
C
OSC
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
theory will explain how the LTC1144 behaves. The loss,
BOOST
10X
OSC
(1)
(7)
EXTERNAL
OSCILLATOR
Figure 3. Switched-Capacitor Equivalent Circuit
SHDN
OSC
(6)
Figure 4. LTC1144 Switched-Capacitor
Voltage Converter Block Diagram
R
R
EQUIV
V1
L
15V
(8)
V
V
+
+
2
+
=
R
I
I
f C1
S
L
C2
10 F
EQUIV
1
1144 F01
V
OUT
SW1
C2
C1
R
CAP
CAP
GND
L
(3)
(2)
(4)
1144 F03
V2
+
–
+
LTC1144
SW2
V
(5)
OUT
1144 F04
5
+
C2