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ALD810023 参数 Datasheet PDF下载

ALD810023图片预览
型号: ALD810023
PDF下载: 下载PDF文件 查看货源
内容描述: QUAD超级电容器自动平衡( SABA ?? ¢ ) MOSFET阵列 [QUAD SUPERCAPACITOR AUTO BALANCING (SAB™) MOSFET ARRAY]
分类和应用: 电容器局域网
文件页数/大小: 17 页 / 523 K
品牌: ALD [ ADVANCED LINEAR DEVICES ]
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GENERAL DESCRIPTION (cont.)  
when it is at 2.7V. The primary benefit here is that this process of  
For stacks of series-connected supercaps consisting of more than  
three or four supercaps, it is possible to use a single SAB MOSFET  
array for every three or four supercap stacks connected in series.  
Multiple SAB MOSFET arrays can be arrayed across multiple  
supercap stacks to operate at higher operating voltages. It is  
important to limit the voltage across any two pins within a single  
SAB MOSFET array package to be less than its absolute  
maximum voltage and current ratings.  
leakage balancing is fully automatic and works for a variety of  
supercaps, each with a different leakage characteristic profile of its  
own.  
A second benefit to note is that with ~2.4V and ~2.6V across the  
two supercaps, in this example, the actual current level difference  
between the top and the bottom SAB MOSFETs is at about a 100:1  
ratio (~2 orders of magnitude). The net additional leakage current  
contributed by theALD8110026 in the design example above would,  
therefore, be approximately 0.01µA. In this case, the difference in  
leakage currents between the two supercaps can have a ratio of  
100:1 and could still have charge balancing and voltage regulation.  
ENERGY HARVESTING APPLICATIONS  
Supercaps offer an important benefit for energy harvesting appli-  
cations from a low energy source, buffering and storing such  
energy to drive a higher power load.  
The dynamic response of a SAB MOSFET circuit is very fast, and  
the typical response time is determined by the R C time constant of  
the equivalent ON resistance value of the SAB MOSFET and the  
capacitance value of the supercap. In many cases the R value is  
small initially, responding rapidly to a large voltage transient by  
having a smaller R C time constant. As the voltages settle down,  
the equivalent R increases. As these R and C values can become  
very large, it can take a long time for the voltages across the  
supercaps to settle down to steady state leakage current levels.  
The direction of the voltage movements across the supercap,  
however, would indicate the trend that the supercap voltages are  
moving away from the voltage limits.  
For energy harvesting applications, supercap leakage currents are  
a critical factor, as the average energy harvesting input charge must  
exceed the average supercap internal leakage currents in order for  
any net energy to be harvested and saved. Often times the input  
energy is variable, meaning that its input voltage and current  
magnitude is not constant and may be dependent upon a whole set  
of other parameters such as the source energy availability, energy  
sensor conversion efficiency, etc.  
For these types of applications, it is essential to pick supercaps  
with low leakage specifications and to use SAB MOSFETs that  
minimize the amount of energy loss due to leakage currents.  
PARALLEL-CONNECTED AND SERIES-CONNECTED SAB  
MOSFETS  
For up to 90% of the initial voltages of a supercap used in energy  
harvesting applications, supercap charge loss is lower than its  
maximum leakage rating, at less than its max. rated voltage. SAB  
MOSFETs used for charge balancing, due to their high input thresh-  
old voltages, would be completely turned off, consuming zero drain  
current while the supercap is being charged, maximizing any  
energy harvesting gathering efforts. The SAB MOSFET would not  
become active until the supercap is already charged to over 90%  
of its max. rated voltage. The trickle charging of supercaps with  
energy harvesting techniques tends to work well with SAB MOSFETs  
as charge balancing devices, as it is less likely to have high  
transient energy spurts resulting in excessive voltage or current  
excursions.  
In the previous design example, note that theALD810026 is a quad  
pack, with four SAB MOSFETs in a single SOIC package. For a  
standard configuration of two supercaps connected in series, the  
ALD9100xx dual SAB MOSFET is recommended for charge  
balancing. If a two-stack supercap requires charge balancing, then  
there is also an option to parallel-connect two SAB MOSFETs of a  
quad ALD8100xx for each of the two supercaps. Parallel-connec-  
tion generally means that the drain, gate and source terminals of  
each of two SAB MOSFETs are connected together to form a  
MOSFET with a single drain, a single gate and a single source  
terminal with twice the output currents. In this case, at a nominal  
operating voltage of 2.50V, the additional leakage current contribu-  
tion by the SAB MOSFET is equal to 2 x 0.1µA = 0.2µA. The total  
current for the supercaps and the SB MOSFET is = 2.5µA + 0.2µA  
~= 2.7µA @ 2.50V operating voltage. At max. voltage of 2.70V  
If an energy harvesting source only provides a few µA of current,  
the power budget does not allow wasting any of this current on  
capacitor leakage currents and power dissipation of resistor or  
operational amplifier based charge-balancing circuits. It may also  
be important to reduce long term leakage currents, as energy  
harvesting charging at low levels may take up to many days.  
across the SAB MOSFET, V  
= V = 2.70V results in a drain  
GS  
DS  
current of 2 x 10µA = 20µA. So this configuration would be chosen  
to increase max. charge balancing leakage current at 2.70V to 20µA,  
at the expense of an additional 0.1µA leakage at 2.50V.  
In summary, in order for an energy harvesting application to be  
successful, the input energy harvested must exceed all the energy  
required due to the leakages of the supercaps and the charge-  
balancing circuits, plus any load requirements. With their unique  
balancing characteristics and near-zero charge loss, SAB MOSFETs  
are ideal devices for use in supercap charge-balancing in energy  
harvesting applications.  
This method also extends to four supercaps in series, although this  
may require two separate ALD810026 packages, if the maximum  
voltage ratings of the SAB MOSFET are exceeded.  
ALD810023, ALD810024, ALD810025,  
ALD810026, ALD810027, ALD810028  
Advanced Linear Devices, Inc.  
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