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User manual for APPEB1002 Revision 2.1, Oct 2019
General Purpose CAP-XX Supercapacitor Evaluation Board
connecting pins 5 & 6 of JP1, and leave solder jumper I Limiter ENABLE (SJ2) and Soft-Start
ENABLE (SJ1) open as shown on the left of figure 6. The PCB trace can withstand a maximum 5A
continuous current. This must be considered when using the direct charge option.
Soft-start charging
To enable charging via the low-cost CAP-XX soft-start circuit, place the jumper link on the second
row of the header marked Soft-start connecting pins 3 & 4 of JP1, leave solder jumper I Limiter
ENABLE (SJ2) open and solder a bridge connecting Soft-Start ENABLE (SJ1) as shown in the
middle of figure 6.
The sub circuit containing R1, R2, M1 and M2 is the soft-start cell charging design. Initially PFET
M1 is ON and the supercapacitor charges through power resistor R2, default value 5.6Ω. When the
supercapacitor charges to ~400mV below the input voltage, M1 will turn OFF, enabling R1 to pull
gate of PFET M2 to 0V, turning M2 ON which effectively short circuits the positive input terminal to
the positive terminal of the supercapacitor. For more information of the operation of this circuit
please refer to the Simple soft-start circuit in CAP-XX Application Note AN1001_Current_Limit Rev
4.0, available on
our
website.
Constant current limit charging
To enable charging through the TPS2553 constant current limit IC, place the jumper link on the
third row of the header marked I limiter connecting pins 1 & 2 of JP1, leave solder jumper Soft-
Start Enable (SJ1) open and solder a bridge connecting I Limiter ENABLE (SJ2) as shown on the
right of figure 6.
Components C6, IC1, R3 and C2 forms the constant current charging option. Solder jumper SJ2
connects this sub circuit to the supercapacitor. IC1, TPS2553 is a power distribution switch with
active constant current limit. Its current limit level is determined by R3, default value is 47kΩ for a
current limit of 556mA. However, this can be easily changed to any desired resistor, either an SMD
0603 or 5mm pitch through hole resistor. Since this IC may throttle its current limit level when it
gets hot, the charging time could be significantly longer than calculated if set current limit is too
high. The current limit threshold equation is given in the IC's datasheet as:
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For more information regarding on this circuit refer to the Integrated Current Limit Solution in in
CAP-XX Application Note AN1001_Current_Limit Rev 4.0, available on
our
website. For more
information
on
the
TPS2553,
please
refer
to
Texas
Instrument's
webpage
http://www.ti.com/product/TPS2553
© CAP-XX Pty Limited 2019 | Tel +61 2 9420 0690 | www.cap-xx.com
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