Page 19 - Issue 4 2023

ELECTRONICS
Figure 4: A CN0509 max charge current vs. VIN.
in the range of 5 V to 100 V. For all of the above reasons,
this makes it an ideal candidate to pair up with the existing
boards to provide the USB charging outputs required for the
power bank charger.
Reverse polarity protection is included to protect the circuit
Figure 6: A system diagram of the prototype.
Figure 5: The power bank charger application tree.
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from an incorrectly connected supply and an isolated
flyback converter is utilised to isolate the charger outputs
from the input source – this is particularly useful if a
–48 V communication backup supply is used as a power
source. This can result in a phone being charged to –48
V and creating a hazardous situation. Isolated conversion
prevents this from occurring. Another note here is that the
CN0509 board is quite small; much of this is attributed to
the highly efficient ICs selected and the no-opto flyback
LT8302. A key differentiation is that the flyback converter
LT8302 does not need an isolated optical feedback path.
There are two USB ports on this particular board:
one is a standard USB port (without D+/D– connected)
and the other port has a DCP controller to monitor the
USB data line voltages so that it can enable fast charging
and provide 5 V at 2 A max. Achieving this higher level of
charge current is dependent on the input voltage utilized.
12 V is optimal based on the performance graph shown in
Figure 4.
Power Sources
The primary power source selected was a 60 W AC-to-DC
12 V adaptor. This served as one input to the LTC4416
demo board, and a relatively small solar panel was
purchased to provide an alternative input source – since
this project was to be used at an indoor event and there
was never going to be sufficient lighting available to
provide a reasonable level of available power to run from
solar, this feature was included simply to demonstrate the
capability and functionality of the power path prioritiser.
This particular design was developed to be a power
bank and as such it would require a battery pack to act
as the storage element. Shipping restrictions in relation
to batteries are prohibitive. The demo was developed
specifically so that a generic battery pack could be bought
and inserted to run the demo on its arrival. Based on this
limitation, a rechargeable 2× series cell Li-Ion battery pack
generating a nominal 7.4 V with a 2600 mAh capacity was
selected to run the demo for the event. It is worth noting
that a larger capacity battery could easily be installed here
if required.
EngineerIT Issue 4 | 2023 | 19