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| 型号： | LTC1046IS8#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 5/12页 |
| 文件大小： | 0K |
| 描述： | IC REG SWITCHD CAP DIV INV 8SOIC |
| 标准包装： | 100 |
| 类型： | 切换式电容器（充电泵），分配器，反相 |
| 输出数： | 1 |
| 输入电压： | 1.5 V ~ 6 V |
| 频率 - 开关： | 5.5kHz ~ 30kHz |
| 电流 - 输出： | 50mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
| 供应商设备封装： | 8-SOIC |
| 产品目录页面： | 1339 (CN2011-ZH PDF) |
LTC1046
A PPLICATI
Theory of Operation
S I FOR ATIO
Examination of Figure 4 shows that the LTC1046 has the
To understand the theory of operation of the LTC1046, 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, 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).
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 typical curve), this simple
theory will explain how the LTC1046 behaves. The loss,
and hence the efficiency, is set by the output impedance.
As frequency is decreased, the output impedance will
eventually be dominated by the 1/fC1 term and power
efficiency will drop. The typical curves for power effi-
ciency versus frequency show this effect for various capaci-
tor values.
Note also that power efficiency decreases as frequency
goes up. This is caused by internal switching losses which
V1
f
V2
occur due to some finite charge being lost on each
switching cycle. This charge loss per unit cycle, when
C1
C2
R L
1046 F02
multiplied by the switching frequency, becomes a current
loss. At high frequency this loss becomes significant and
the power efficiency starts to decrease.
Figure 2. Switched Capacitor Building Block
Rewriting in terms of voltage and impedance equivalence,
V +
(8)
SW1
SW2
CAP +
( )
I =
V 1 – V 2
1 / fC 1
=
V 1 – V 2
R EQUIV
.
BOOST
3x
(1)
OSC
+2
φ
(2)
+
C1
A new variable, R EQUIV , has been defined such that
OSC
(7)
φ
CAP –
(4)
V OUT
(5)
R EQUIV = 1/fC1. Thus, the equivalent circuit for the switched
capacitor network is as shown in Figure 3.
C2
V1
R EQUIV
V2
LV
(6)
CLOSED WHEN
V + > 3.0V
GND
(3)
1046 F04
R EQUIV = 1
fC1
C2
R L
Figure 4. LTC1046 Switched Capacitor
Voltage Converter Block Diagram
1046 F03
Figure 3. Switched Capacitor Equivalent Circuit
1046fb
5
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