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| 型号： | LTC3240EDC-3.3#TRMPBF |
| 厂商： | Linear Technology |
| 文件页数： | 8/12页 |
| 文件大小： | 0K |
| 描述： | IC REG MULTI CONFIG 3.3V 6DFN |
| 标准包装： | 1 |
| 类型： | 降压（降压），升压（升压），切换电容（充电泵） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 3.3V |
| 输入电压： | 1.8 V ~ 5.5 V |
| PWM 型： | Burst Mode? |
| 频率 - 开关： | 1.2MHz |
| 电流 - 输出： | 150mA |
| 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： | 剪切带 (CT) |
| 供应商设备封装： | 6-DFN-EP（2x2） |
| 产品目录页面： | 1339 (CN2011-ZH PDF) |
| 其它名称： | LTC3240EDC-3.3#TRMPBFCT |
LTC3240-3.3/LTC3240-2.5
APPLICATIO S I FOR ATIO
= = OUT
η=
I OUT =
Power Ef?ciency
During LDO operation, the power ef?ciency ( η ) of the
LTC3240 is given by:
P OUT V OUT ? I OUT V
P IN V IN ? I OUT V IN
At moderate to high output power, the quiescent cur-
rent of the LTC3240 is negligible and the expression
above is valid. For example, the measured ef?ciency of
LTC3240-3.3, with V IN = 3.7V, I OUT = 100mA and V OUT
For the LTC3240 in charge pump mode, the maximum
available output current and voltage can be calculated
from the effective open-loop output resistance, R OL , and
the effective output voltage, 2V IN(MIN) .
From Figure 1, the available current is given by:
2V IN – V OUT
R OL
Typical R OL values as a function of temperature are shown
in Figure 2.
regulating to 3.3V is 87% which is in close agreement
with the theoretical value of 89%.
R OL
+
During charge pump operation, the power ef?ciency ( η )
of the LTC3240 is similar to that of a linear regulator with
an effective input voltage of twice the actual input volt-
+
–
2V IN
I OUT
–
V OUT
age. This occurs because the input current for a voltage
doubling charge pump is approximately twice the output
3240 F01
Figure 1. Equivalent Open-Loop Circuit
current. In an ideal regulating voltage doubler the power
ef?ciency is given by:
10
V IN = 1.8V
V OUT = 3V
= = OUT
η=
P OUT
P IN
V OUT ? I OUT V
V IN ? 2 I OUT 2 V IN
9
8
At moderate to high output power, the switching losses
and the quiescent current of the LTC3240 are negligible
and the expression above is valid. For example, the mea-
sured ef?ciency of LTC3240-3.3 with V IN = 2.5V, I OUT =
7
6
100mA and V OUT regulating to 3.3V is 64% which is in
close agreement with the theoretical value of 66%.
5
–40
–15
10 35
TEMPERATURE ( ° C)
60
85
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
depends on many factors such as the oscillator frequency
(f OSC ), value of the ?ying capacitor (C FLY ), the nonoverlap
time, the internal switch resistances (R S ), and the ESR of
the external capacitors. A ?rst order approximation for
3240 G07
Figure 2. Typical R OL vs Temperature
V IN , V OUT Capacitor Selection
The style and value of capacitors used with the LTC3240
determine several important parameters such as regulator
control loop stability, output ripple, charge pump strength
and minimum start-up time.
R OL is given below:
R 0 L ? 2 ∑ R S +
S = 1 TO 4
1
f OSC ? C FLY
To reduce noise and ripple, it is recommended that low
ESR (<0.1 Ω ) ceramic capacitors be used for both C IN and
C OUT . C IN should be 1μF or greater while C OUT should be
4.7μF or greater. Tantalum and aluminum capacitors are
not recommended because of their high ESR.
3240fb
8
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