I am looking at designing a converter based on the 28950, and hopefully migrate to a DSP, but I have a question about the current sensing.
I have been using the excel design tool (sluc222b) which is making life a lot easier, but I have a problem with a large primary current, the application will result in a peak current of about 150A (Ipp in the design tool). Obviously measuring this isn't going to be easy but I was wondering if anyone has ever used current sense resistors and an amplifier instead of of current transformer. Do you know of any issues that will or are likely to crop up if I tried (a lot of) current sense resistors and an amplifier instead of the current transformer.
I understand that it needs to be configured to produce 2V at the peak current to allow the current limiting aspect of the 28950 to work. The reason I ask is that even looking at a current transformer it will be difficult to measure the current without generating a lot of loss in the sense side circuitry, and a surface mount option is much more desirable that through-hole.
We're using the Si8503 [SO-20], but that's below 20A.. and then a small OPA830D amplifier to match the voltages for the UCC28950.
Thanks for the reply, we already used an INA139 elsewhere so I will have a try with that.
On the excel design tool certain parameters are locked, obviously to stop them being messed with, unfortunately as I'm doing a boost version these parameters aren't valid for out application. Is there a way of getting the password or an unlocked version of the tool?
Are you sure that your INA139 i quick enough to respond to the current and then make the UCC28950 regulate from that? As I can see, the response time is 20us for the INA139 when G=100.. Make sure your gain i small. See page 5 the 4 figures on top.
I hadn't got far enough to look at that, the gain will be between 10 and 20 so it's looking pretty marginal. Going to have another look for a current sense, anything spring to mind?
If you're not using the Si85XX, then a solution with the THS4281 could be a solution with a shunt resistor. This circuit is found the the e2e community if you search UCC28070 and current sense.
Thanks for the response.
I have been looking at the circuit, trying to determine if noise suppression would be required in my application, if not, what the circuit would look like.
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