Adafruit has breakouts for 2 different PWM driver:
The specific differences I'm interested in are the ones that would make the former suitable for LEDs and the latter also suitable for servos. The description of the SPI one says "Designed (and ideal) for LED control, this board is not good for driving servos."
What causes that difference? What should I look for in datasheets to understand if I can use a PWM controller to drive servos?