SABMB16/SABMB810025/SABMB910025 Advanced Linear Devices, Inc. 2 of 4
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
with a value equal to 0
Ω or use an external wire.
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
