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參數(shù)資料
| 型號： | LM2760 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | ER 2C 2#16S SKT PLUG |
| 中文描述： | 3.3V的穩(wěn)壓開關(guān)電容電壓轉(zhuǎn)換器 |
| 文件頁數(shù)： | 9/10頁 |
| 文件大?。?/td> | 242K |
| 代理商： | LM2760 |
Application Information
(Continued)
1mA). The simplified power model of the LM2760, in
Figure
2
, will be used to discuss power efficiency and power dissi-
pation.
In calculating power efficiency, output power (P
) is easily
determined as the product of the output current and the 3.3V
output voltage. Like output current, input voltage is an
application-dependent variable. The input current can be
calculated using the principles of linear regulation and
switched capacitor conversion. In an ideal linear regulator,
the current into the circuit is equal to the current out of the
circuit. The principles of power conservation mandate the
ideal input current of a voltage converter must be equal to
the product of the gain of the converter and the output
current. When the input voltage is low (V
IN
≤
3.4V) and the
LM2760 is in doubler mode (2x), the gain of the converter is
2. At higher input voltages (V
IN
>
3.4V typ.) where the
LM2760 is in pass mode (1x), the gain of the converter is 1.
Adding a correction factor for supply current when the pump
is continuously active (I
, 0.3mA typ.) gives an approxi-
mation for total input current which, when combined with the
other input and output parameter(s), yields the following
equations for efficiency:
A plot of efficiency versus input voltage, contained in
Figure
4
, gives a clear indication of how the pass mode improves
efficiency of the part at higher input voltages. Efficiency of
the part in both doubler and pass modes is inversely propor-
tional to input voltage, highest when the input voltage is low.
When the part transitions to pass mode, however, there is a
boost in efficiency that is a result of the reduced input current
needed for the 1x-configured converter. This multi-gain to-
pology maximizes LM2760 efficiency over the Li-Ion battery
input range: the average efficiency of the part over a 3.0V-
to-4.2V input range is 75% (1mA
≤
I
OUT
≤
20mA).
Comparisons of LM2760 efficiency measurements to calcu-
lations using the above equations have shown the equations
to be quite accurate approximations of actual efficiency
when output currents are at or above 1mA. Under these
conditions, the pump is on nearly continuously, and PFM-
related rest states are infrequent. At lighter loads, however,
pulse frequency modulation has a greater impact on part
performance. With PFM, the part only pumps when it needs
to boost the output voltage. Otherwise, it idles in a low-
current rest mode. PFM reduces the input current of the part
(effectively reducing I
PUMP
), improving the efficiency of the
part at lighter loads.
POWER DISSIPATION
LM2760 power dissipation (P
) is calculated simply by sub-
tracting output power from input power. Maximum power
dissipation of the LM2760 occurs at the high end of the
doubler mode (V
= 3.4V). The following equation can be
used to estimate power dissipation of the LM2760 when in
doubler mode:
P
D-2X
= P
IN
- P
OUT
= [V
IN
x (2·I
OUT
+ I
PUMP
)] - [V
OUT
x I
OUT
],
where I
PUMP
is the supply current when the pump is continu-
ously active (0.3mA typ.).
Neglecting conditions outside the specified operating rat-
ings, maximum power dissipation of the LM2760 is approxi-
mately 70mW (V
IN
)
3.4V, I
OUT
= 20mA, I
PUMP
= 0.3mA).
When the junction-to-ambient thermal resistance of the
LM2760 in the application is 220
o
C/W (matches JEDEC
JESD51-3), power dissipation results in a 15
o
C elevation
above ambient in the junction temperature of the part. Thus,
when the ambient temperature is 85
o
C, the junction tem-
perature of the LM2760 under these conditions will be
100
o
C. LM2760 performance limits are guaranteed over a
junction temperature range of 0
o
C to +70
o
C. The LM2760
must be operated with a junction temperature within this
range for the guaranteed performance limits listed in this
datasheet to apply.
20044304
FIGURE 2. LM2760 Power Model
20044307
FIGURE 3.
20044305
FIGURE 4. LM2760 Power Efficiency vs. Input Voltage
(T
A
= 25
o
C)
L
www.national.com
9
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| LM2760M5X/NOPB | 功能描述:IC REG BST SWITCHED CAP SOT23-5 RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:1 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:3.3V 輸入電壓:4.5 V ~ 24 V PWM 型:- 頻率 - 開關(guān):- 電流 - 輸出:125mA 同步整流器:無 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:SOT-23-6 包裝:Digi-Reel® 供應(yīng)商設(shè)備封裝:SOT-6 其它名稱:MAX1836EUT33#TG16DKR |
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