SABMB16/SABMB810025/SABMB910025

Advanced Linear Devices, Inc.

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SABMB8100XX/SABMB9100XX

The ALD8100XX/ALD9100XX SAB MOSFET family offers the user

a selection of different threshold voltages for various

supercapacitor nominal voltage values and desired leakage

balancing characteristics. Each SAB MOSFET generally requires

connecting its V+ pin to the most positive voltage and its V- and

IC pins to the most negative voltage within the package. Note

that each Drain pin has an internal reverse biased diode to its

Source pin, and each Gate pin has an internal reverse biased

diode to V-. All other pins must have voltages within V+ and V-

voltage limits within the same package unit. Standard ESD

protection facilities and handling procedures for static sensitive

devices must also be used while installing the ALD8100XX or

ALD9100XX units. Once installed, the connection configuration

will protect the ALD8100XX/ALD9100XX units from ESD damage.

When connected to a supercapacitor stack, the ALD8100XX/

ALD9100XX is further protected from virtually any ESD damage

due to the large capacitance of the supercapacitors, which sinks

any ESD charge and thereby reduces any of the terminal voltages

to minimal harmless values.

SABMB16 PRINTED CIRCUIT BOARDS

The SABMB16 Printed Circuit Board is supplied as a blank PCB

board, made with RoHS compliant FR4 material, ready for

mounting of up to two 8-lead ALD9100XX units or one 16-lead

ALD8100XX unit. It is also supplied and available with a 6 digit

suffix, which denotes the specific ALD9100XX or ALD8100XX

component mounted and tested on the PCB. All that is required

for the user to perform is mount the PCB and wire the appropriate

connections from the SABMB16 board to the respective

supercapacitor nodes.

Each SABMB16 Printed Circuit Board has two 8-lead SOIC

footprints for up to two ALD9100XX units. It also has a 16-lead

SOIC footprint for an ALD8100XX which is parallel connected to

the two ALD9100XX footprints (See schematic diagram). Each

SABMB16 PCB has terminals labeled V+, A, B, C, D, E and V-.

Each of these terminals has two wiring holes for easier connection

of the same terminal node to two external connection points. V+

is directly connected to terminal A, which must be connected to

the most positive voltage for the individual SABMB16 PCB board.

V- is directly connected to terminal E, which must be connected

to the most negative voltage present for the same SABMB16

board. All other terminals, namely B, C and D, must have voltages

between V+ and V- for the board. When cascade or daisy-chain

connected, each SABMB16 board is self-contained and rated for

15.0V maximum.

When two supercapacitors are installed to be balanced by SAB

MOSFETs, a single ALD9100XX unit can be mounted on either

one of two 8-lead SOIC footprints on the SABMB16. The user

then needs to connect the unused circuit traces to the appropriate

terminals so that V+ and V- remain the most positive voltage and

the most negative voltage for that SABMB16 board, respectively.

For example, if only one ALD9100XX is used for the upper SOIC

footprint, terminal C can be connected to terminal E, or V-. One

convenient way to make this connection on board is to install R2

Any number of SABMB16 boards can be daisy-chain connected

in series. For example, three SABMB16 boards, each with an

ALD810025SCLI installed, can be connected in series to a 30V

power supply, provided care is taken to insure that each SABMB16

board V- is connected to the V+ of the next SABMB16 board in

series, such that each board would not have internal voltages from

V+ to V- exceeding 10V (30V/3 = 10V).

The ALD8100XX/ALD9100XX is rated for reverse bias diode

currents of up to 80 mA maximum for each SAB MOSFET on board.

Any reverse bias condition as a result of changing supercapacitor

voltages, especially during fast supercapacitor discharge, could

lead to some internal nodes temporally reverse biased with surge

current in excess of this limit. The SABMB16 board has additional

optional TO277 footprints for mounting external schottky rectifiers

(power diodes) to clamp such current transients. The user is

advised to determine the various power and current limits, including

temperature and heat dissipation considerations, when selecting

a suitable component for such purpose. The appropriate level of

derating and margin allowance must also be added to assure long

term reliability of the PCB board.

SUPERCAPACITORS

Supercapacitors are typically rated with a nominal recommended

working voltage established for long life at their maximum rated

operating temperature. Excessive supercapacitor voltages that

exceed its rated voltage for a prolonged time period will result in

reduced operating life and eventual rupture and catastrophic

failure. To prevent such an occurrence, a means of automatically

adjusting (charge-balancing) and monitoring the maximum voltage

is required in most applications having two or more supercapacitors

connected in series, due to their different internal leakage currents

that vary from one supercapacitor to another.

The supercapacitor leakage current itself is a variable function of

its many parameters such as aging, initial leakage current at zero

input voltage, the material and the construction of the

supercapacitor. Its leakage is also a function of the charging

voltage, the charging current, operating temperature range and

the rate of change of many of these parameters. Supercapacitor

balancing must accommodate these changing conditions.

ENERGY HARVESTING APPLICATIONS

Supercapacitors offer an important benefit for energy harvesting

applications from a low energy source, buffering and storing such

energy to drive a higher power load.

For energy harvesting applications, supercapacitor leakage

currents are a critical factor, as the average energy harvesting

input charge must exceed the average supercapacitor internal

leakage currents in order for any net energy to be harvested and

saved. Often, the input energy is variable, meaning that its input

voltage and current magnitude are not constant and may be

dependent upon a whole set of other parameters such as the

source energy availability, energy sensor conversion efficiency,

etc.

SAB MOSFETs used for charge balancing, due to their high input

threshold voltages, would be completely turned off, consuming

zero drain current while the supercapacitor is being charged,

SUPERCAPACITOR AUTO BALANCING PCB