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参数资料
| 型号： | LTC3221EDC#TRMPBF |
| 厂商： | Linear Technology |
| 文件页数： | 7/12页 |
| 文件大小： | 0K |
| 描述： | IC REG SWITCHED CAP DBL ADJ 6DFN |
| 标准包装： | 500 |
| 类型： | 切换式电容器（充电泵），倍增器 |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调 |
| 输入电压： | 1.8 V ~ 5.5 V |
| PWM 型： | Burst Mode? |
| 频率 - 开关： | 600kHz |
| 电流 - 输出： | 60mA |
| 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： | 6-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 6-DFN-EP（2x2） |
LTC3221/
LTC3221-3.3/LTC3221-5
OPERATIO
(Refer to Block Diagrams)
The LTC3221 has a FB pin in place of the ? S ? H ? D ? N pin. This
allows the output voltage to be programmed using an
V OUT stays above this lower threshold for a long period of
time, this result in a very low average input current.
external resistive divider.
Soft-Start and Short-Circuit Protection
I OUT =
Burst Mode Operation
The LTC3221 family regulates the output voltage throughout
the full 60mA load range using Burst Mode control. This
keeps the quiescent current low at light load and improves
the ef?ciency at full load by reducing the switching losses.
All the internal circuitry except the comparator is kept off
if the output voltage is high and the ?ying capacitor has
been fully charged. These circuits are turned on only if V OUT
drops below the comparator lower threshold. At light load,
APPLICATIO S I FOR ATIO
Power Ef?ciency
The input current of a doubling charge pump like the LTC3221
family is always twice that of the output current. This is
true regardless of whether the output voltage is unregulated
or regulated or of the regulation method used. In an ideal
unregulated doubling charge pump, conservation of energy
implies that the input current has to be twice that of the
output current in order to obtain an output voltage twice
that of the input voltage. In a regulated charge pump like
the LTC3221, the regulation of V OUT is similar to that of a
linear regulator, with the voltage difference between 2 ? V IN
(Input voltage plus the voltage across a fully charged ?ying
capacitor) and V OUT being absorbed in an internal pass
transistor. In the LTC3221, the controlled current I SW acts as
a pass transistor. So the input current of an ideal regulated
doubling charge pump is the same as an unregulated one,
which is equal to twice the output current. The ef?ciency
(n) of an ideal regulated doubler is therefore given by:
The LTC3221 family uses a controlled current, I SW to
deliver current to the output. This helps to limit the input
and output current during start-up and output short-circuit
condition. During start up I SW is used to charge up the ?ying
capacitor and output capacitor, this limits the input current
to approximately 240mA. During short-circuit condition,
the output current is delivered through I SW and this limits
the output current to approximately 120mA. This prevents
excessive self-heating that causes damage to the part.
the theoretical 83.3% calculation. The LTC3221 product
family continues to maintain good ef?ciency even at fairly
light loads because of its inherently low power design.
Maximum Available Output Current
For the adjustable LTC3221, the maximum available output
current and voltage can be calculated from the effective
open-loop output resistance, R OL , and effective output
voltage, 2V IN(MIN) .
From Figure 1 the available current is given by:
2V IN – V OUT
R OL
Effective Open-Loop Output Resistance (R OL )
The effective open-loop output resistance(R OL ) of a charge
pump is a very important parameter which determines the
strength of the charge pump. The value of this parameter
= = OUT
η=
P OUT
P IN
V OUT ? I OUT V
V IN ? 2 I OUT 2 V IN
R OL
+
At moderate to high output power, the switching losses and
quiescent current of the LTC3221 family are negligible and
the expression is valid. For example, an LTC3221-5 with V IN
= 3V, I OUT = 60mA and V OUT regulating to 5V, has a mea-
+
–
2V IN
3221 F01
I OUT
–
V OUT
sured ef?ciency of 82% which is in close agreement with
Figure 1. Equivalent Open-Loop Circuit
3221f
7
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