STP16CPS05 Sink Driver External Resistor does not change output current
I'm wondering if you are just caught with the LED forward voltage, VF, the supply voltage, the PNP voltage drop and the current regulator.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Equivalent circuit.

If you can repeat your long-delay code and measure the voltages with respect to ground for VCC and the LED anode and cathode we may be able to make some sense of your observations.



Figure 13 of the datasheet suggests that the voltage drop across the current sink will rise with the current. This is to be expected.



Figure 3. VF for various LED colours. Image source (mine).

We can also see that as the current increases that VF will rise also. The combination of the current sink drop, the LED increasing VF and the fixed drop across the PNP transistor may put you into current limit.

Unfortunately with your PNP arrangement you can't supply the LED array with a higher voltage or you will experience a high-side fail.