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I'm designing a circuit where I'll run a 3W LED using the CAT4101 Led driver, like in the in picture below. VCC will be a 2s Li-Ion battery, at 8.4 - 7.2V DC.

CAT4101 LED Driver

As I'll use PWM to DIM the led, there'll be a lot of fast on's and off's between the VCC line (LED +) and the LED - pin (which is not directly a GND pin).

If I connect a LDO to get the 8.4V VCC to 5V (maybe an ALS1117 LDO, with it's recommended capacitors) between the VCC and GND, to run an MCU at 5V and also to power the VIN pin of the CAT4101 (which needs 5V), would this fast switching by the PWM on the VCC line through the LED cause any problems to get a stable 5v output on the LDO?

Can I use the VCC normally to supply other circuits, independent of the led state, if it's on, off, or being PWM'd?

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  • \$\begingroup\$ You're asking if you can power an LDO with 8.4V from batteries, and use the 5V output to power multiple circuits? Yes, you absolutely can. Just make sure it can supply enough current to whatever you're powering, and use the recommended decoupling scheme! \$\endgroup\$
    – earl
    Commented Dec 6, 2022 at 19:42

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Assuming the VCC supply can support the additional current required, it should be no problem. Be sure you have adequate decoupling of the VCC supply at the top of the LED string as well as the Vin pin on the CAT4101, and the recommended input and output caps on the LDO.

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