SABMB2/SABMB2XX

Advanced Linear Devices, Inc.

3 of 4

SUPERCAPACITOR AUTO BALANCING PCB

maximizing any energy harvesting gathering efforts. The SAB

MOSFET does not become active until the supercapacitor is

already charged to over 90% of its max. rated voltage. The trickle

charging of supercapacitors 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.

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.

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 supercapacitors 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 supercapacitor charge-

balancing in energy harvesting applications.

BATTERY POWERED APPLICATIONS

Many battery powered circuits requiring a supercapacitor to boost

power output can benefit from using SAB MOSFETs for

supercapacitor balancing. The additional power burn by using

SAB MOSFETs for supercapacitor stack balancing can actually

be negative, as adding SAB MOSFETs can save supercapacitor

leakage current and associated power dissipation by lowering the

operating bias voltage of the leakier supercapacitor. Applications

that depend on long life battery usage must take into account the

supercapacitor leakage current and balancing circuit power burn

because the currents involved are steady state DC currents that

are continuous throughout the lifetime of the application and its

battery life. The average added power dissipation with the addition

of the SABMB2 board is zero, provided the selection of the

operating voltages and SAB MOSFETs are appropriate for the

leakage currents of the supercapacitors specified.

CONNECTION TO OTHER SABMBXX PCBs

The SABMB2 is compatible with other SABMBXX boards and is

designed to be used along with other SABMBXX boards connected

in series to achieve balancing the corresponding number of

supercapacitors installed in a series stack. For example, five

supercapacitors in series can be balanced with one SABMB2 PCB

and one SABMB16 PCB connected in series.

For more information on the CHARACTERISTICS OF

please refer to the following documents:

* ALD8100XX/ALD9100XX FAMILY of SUPERCAPACITOR

* Individual datasheet for chosen SAB MOSFET.

SABMB2 PCB CONNECTION TO

SUPERCAPACITORS C1, C2

* Magnified, not to scale

CAUTION:

Users must limit the voltage across any ALD9100XX chip to

15.0V max.

U1

V-

A

A

B

B

C

C

V+

SABMB2

V+

V- TO NEXT BOARD V+

C1

C2

VC

VB

VA

U1

V-

A

A

B

B

C

C

V+

SABMB2

V+ TO NEXT BOARD V-

V- TO NEXT BOARD V+

C1

C2

VC

VB

VA

U1

V

A

A

B

B

C

C

V+

SABMB2

V+ TO NEXT BOARD V-

C1

C2

VC

VB

VA