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/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. These units are 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 of the user is to 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, and a 16-lead SOIC

footprint, for one ALD8100XX, which is parallel connected to the

two ALD9100XX footprints (See schematic diagram). It has

terminals labeled V+, A to 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

proper operation of 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 80mA 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 the supercapacitor’s 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 the different

internal leakage currents that vary from one supercapacitor to

another.

Each supercapacitor has a tolerance difference in capacitance,

internal resistance and leakage current. These differences create

imbalance in cell voltages, which must be balanced so that any

individual cell voltage does not exceed its rated max. voltage.

Initially, cell voltage imbalance is caused by capacitance value

differences. Supercapacitors selected from the same manufacturer

make and model batch can be measured and matched to deliver

reasonable initial cell voltages. Next, cell voltage imbalance due

to individual cell leakage currents must be compensated.

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/construction of the supercapacitor, and

the operating bias voltage. 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.

By using the appropriate ALD SAB MOSFET and the appropriate

SABMBXX board, users can compensate for all of these causes

of imbalance and automatically balance supercapacitors.

SUPERCAPACITOR AUTO BALANCING PCB