SABMB16/SABMB810025/SABMB910025

Advanced Linear Devices, Inc.

3 of 4

SABMB8100XX/SABMB9100XX

SUPERCAPACITOR AUTO BALANCING PCB

ENERGY HARVESTING APPLICATIONS

Supercapacitors offer an important benefit for energy harvesting

applications from a low energy source, by 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,

changing environmental conditions, etc.

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

threshold voltages, would be completely turned off initially,

consuming zero drain current while the supercapacitor is being

charged, 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 supercapacior. 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 power dissipation with the addition of the

SABMB16 board is zero, provided the selection of the operating

voltages and SAB MOSFETs are appropriate for the leakage

currents of the supercapacitors specified.

* Magnified, not to scale

CONNECTION TO OTHER SABMBxx PCBs

The SABMB16 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 SABMB16

PCB and one SABMB2 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.

CAUTION:

Users must limit the voltage across any ALD9100XX chip to

15.0V max.

SABMB16 PCB CONNECTION TO

SUPERCAPACITORS C1, C2, C3, C4

A

A

B

B

C

C

D

D

E

E

V+

R1

R2

U3

U2

V-

A

A

B

B

C

C

V+

R1

U2

A

A

B

B

C

C

D

D

E

E

V+

R1

R2

U3

U2

V-

V+

VC

VB

VA

VE

VD

C1

C2

C3

C4

V- TO NEXT BOARD V+

V+ TO NEXT BOARD V-

VC

VB

VA

VE

VD

C1

C2

C3

C4

V- TO NEXT BOARD V+

V+ TO NEXT BOARD V-

VB

VA

C1

C2