What's the max frequency of TL5001a, and what's the min off time.

Martin:

Thank you for the reply. Since I wrote this post, I came across the TPS40200, and I believe that part is a better choice, although more expensive. My desin is high current (50A output) and I'm trying to keep the cost as low as possible. I wanted to run VM control because I didn't want to add the additional cost necessary to sense the switch current. I also wanted to make it sycn, to keep power disipation low.

In general it seems like there isn't a lot of VM boost controllers available, so that's why I've been looking a using buck controllers with aditional circuitry

I planned on using a mosfet driver designed for a sync buck converter (i.e. with a bridge output). The input polarity of those are backwards from what I need, but since the TPS40200's output is meant to drive a PChanel, it's inverted from that the mosfet driver is expecting, so I thought all the polarities will work out. However, if the output of this IC only goes to Vdd - 10, then that will be a problem as my application can go to 14V. I'll have to add a level translator circuit on the output.

I remember seeing that you can make it a current mode converter without additional cost by using the Rds of the switch mosfet, but I've never done that. I suppose I could use the TPS40210, with the mosfet Rds as the current sense, and make it a current mode controller that way. Does that seem like a better idea?  Does TI have VM boost controllers that are more suited to this application?

Patrick,

If I understand correctly your input is 10 to 14V, and your output current is 50A, and given your implied duty cycle then Vout is about 18.5V. If this is correct then your output power is over 900 watts. With that kind of power and current, if you were to design a discontinuous boost, the peak currents would be prohibitive, so likely you would be designing a continuous boost. At 10V in, your DC input current is more than 90A, and the peak AC currents far above that.

Again, if that is true then the design would be better off by using a current mode topology. Otherwise the loop compensation will be a challenge. Indeed, that is why there aren't many VM boost controllers. Even with a current mode, the closed loop bandwidth will be quite low (it must be lower than the RHP zero). Also, with the implied power and current, you will need to measure your current anyway. Any sort of fault or abnormal operation will have catastrophic results on the silicon. You would really want to have pulse-by-pulse current limit in your controller.

With that being said, a normal boost does not have any way of protecting against a load short, so even with pulse-by-pulse current limit you will also need a doomsday protection device like a series fuse.

Let me know if this helps.

MC.

 Martin:

Thanks for your reply, but unfortunately it doesn't really help.  I'm already aware of the power levels and the potential problems you've stated. Currently, I'm doing continuous mode, my compensation is a simple dominate pole roll-off (RHPZ and LC resonance are high enough that I can still get decent BW and PM), and I have a fuse on the input. 

Sensing the high input current can get expensive and/or burn a lot of power, which is why I steered towards VM.  If TI has something better for a VM mode boost, please let me know, because I couldn't find anything.

Going forward, I'll try to switch to CM and use the mosfet rds to sense current. In that case I'll use the TPS40210. I've used that part in the past with good success.   

 Thanks

Hi Patrick,

Given your parameters, I would look at the device UC28023, web page:

http://www.ti.com/product/uc28023

This device can be configured as a VM or CM and has operation beyond the frequency you need.

Thanks,

MC.