PCA9515A Do not use rise-time accelerator

Hello Shu-Cheng,

Thanks for the question.
The point of a rise time accelerator is to accelerator the rising edge (Surprise!)

It does this by turning on a low-resistance path to the power rail for a very short time (about 50-100 ns, generally), to help the bus rise significantly faster.

For example, an RTA might behave like this:
1) Voltage on bus is low (0V)
2) Voltage begins rising. Bus rises slowly because of heavy capacitance or weak pull-up resistor
3) Bus voltage hits 30% of VCC and the rise time accelerator detects this.
4) RTA turns on a short to power rail (through a low resistance path of ~50-300 ohms) for roughly 50 ns or until voltage on bus hits 90% of vcc, then it turns off.

Most devices do not use a RTA, as they can cause issues with the bus rising too quickly and causing noise issues.

Hello Shu-Cheng,

Rise time accelerators (RTAs) or sometimes called edge rate accelerators are used in a lot of parts, such as the TXS family of translators/level shifters.  I like to think of it as a FET across the pull up resistor that gets turned on to reduce the pull up resistance during turn on, which makes for faster transitions.  Here is an image of a part that used rise tire accelerators.

I hope that this is helpful in explains what a RTA is and how it works.