Hello. My name is Darwin Fernandez. I'm an applications engineer supporting TI's Power Over Ethernet Powered Devices. Today's training will discuss "Advanced Startup in TI's Power Over Ethernet Powered Devices."

At a high level, advanced startup is a new feature in TI's PoE PD ICs. It allows for a simple, flexible, and minimal system cost solution to starting up a DC-to-DC converter. And what I hope you get out of this training is that you'll learn the functionality of the TPS2373 and TPS23755, which uses advanced startup, the benefits of advanced startup, and the performance differences between traditional startup and advanced startup.

There are currently two devices that use advanced startup in TI's PoE PD portfolio. The first is the TPS23755, which is a Type 1 primary-side regulation PoE PE with integrated primary switching FET. The second PD controller is the TPS2373, which is in IEEE 802.3.bt-ready device, which can do Type 3 51 watts or Type 4 71 watt power levels and uses advanced startup. Both TPS23755 and TPS2373 are available on TI.com, along with EVMs and TI designs found in their respective product pages. For this training video, we'll be primarily focusing on the TPS2373.

This slide shows the internal block diagram of the TPS2373 on the left and how it's implemented externally on the right. So how does advanced startup work? Once inrush period duration has exceeded the 81 milliseconds, [? PG ?] output becomes high impedance and the PWM controller startup source is turned on to charge the VC_OUT capacitor. This allows the downstream converter circuitry to start.

Note that the startup source current capability is such that it can fully maintain VC_OUT during the converter startup without requiring any significant capacitance. So once VC_IN has risen above the VC_IN threshold, around 8.5 volts, meaning that the DC-to-DC converter has wrapped up its output voltage, VC_IN then is internally connected to VC_OUT. The startup current source is then turned off at around 24 milliseconds afterwards, completing the startup.

If there is a fault condition preventing VC_IN from rising above the converter startup, for example, if there is a short on the output of the downstream converter, at around 50 milliseconds there is a timeout period. And it's applied at the end, of which the startup source is turned off and the VC switch is turned on until VC_OUT falls below the UVLO to initiate a new startup cycle.

So how does all of this affect your converter design? So there are many considerations when designing a DC-to-DC converter solution. One consideration is startup.

Here's an example of a typical converter solution on the left. The PWM controller connects to a high-voltage rail, so you typically need a bootstrap design to help turn on the PWM controller. Next, as the converter starts switching, the gate charge of the fence make for a large bias cap to maintain the voltage rail up so that the converter does not shut down.

This is where TI's solution on the right helps mitigate many drawbacks in power converter design. Rather than a high-voltage connection, TI's advanced startup circuit allows the PD to provide the initial power to the PWM controller, and therefore, there's no need for a high-voltage rail or a high-voltage controller. The converter starts switching. And the bias winding ramps up and the PD will sense the bias winding voltage. And when it reaches a certain threshold, the PD will turn on its back-to-back FETs.

Now, the bias winding is providing power to the PWM controller and the converter is self-powering. And you'll notice, since the PD will provide power to the PWM controller, you no longer need a large, bulky bias winding cap. With this solution, we've tested with one microfarad ceramic at the PWM controller.

This slide summarizes the benefits of advanced startup that I've discussed from the past two slides. It's consolidated here. And the focus really is a solution for cost savings, a smaller size, and also interoperability.

So lastly, I wanted to show the benefit of advanced startup versus not using advanced startup under the same conditions. For example, these are both using an active clamp forward converter design and the output voltages are the same, 5 volts. And this is only using-- both using 1 microfarad ceramic cap at the PWM controller.

So on the left, we see a successful startup, while on the right, without event startup, the PWM controller is unable to get into normal operation only because the 1-microfarad cap cannot provide the energy to have the FET switch continuously, and so it oscillates on and off.

And that is it. We hope this training on advanced startup was helpful from a converter-design perspective. I recommend looking at our TI Design Library for our PoE reference designs that use the TPS2373 and the TPS23755. We also have TI.com/PoE to look at for the latest and greatest ICs and app notes on PoE. Or you could also use the E2E community for application support, or direct questions for me regarding PoE. Once again, thank you, and have a nice day.