Max Loading on BS2

skylight

To quote the BS Manual:
General-purpose I/O pins: each can sink 25 mA and source 20mA. However, the total of all pins should not exceed 50 mA (sink)
and 40 mA (source) if using the internal 5-volt regulator. The total per 8-pin groups (P0 – P7 or P8 – 15) should not exceed 50 mA
(sink) and 40 mA (source) if using an external 5-volt regulator.
This suggests that with four outputs spread evenly over the two·groups· means i can drive four Leds(20ma) using an external regulated supply to VDD utilising one BS2 stamp, I am also using these outputs to drive an L293D chip whose input loads are negligible on the stamp, is there a problem with running the BS2 at this max loading indefinitely or is there a duty cycle?
regards

Mike Green

There's no duty cycle involved and, as long as you keep within these limits, you should be fine.

The pin group limits have to do with the current carrying capacity of the wiring on the processor chip itself.

The individual pin limits have to do both with the current carrying capacity of the wiring on the chip and the
current carrying capacity of the output transistors for the pin.

The total Stamp capacity using the internal regulator has to do with the regulator on the Stamp substrate
and the regulator will shut down if the output current exceeds this (or if it overheats trying to dissipate
a high input voltage differential: (Vin - 5.0) * output current).

skylight

Thanks Mike

allanlane5

20 mA is a lot for an LED. Most will get 'full bright' at about 12 mA. This might help your power limitations.

skylight

Thanks