Vicor power module ...powering the external error amplifier?

[treez]

The PRM48 power module datasheet (page 2) shows the external error amplifier being powered by the VAUX pin. Does it have to be so?....can we not power it from an external 9V supply? Does the error amp have to be powered down when the PRM48 module is in disable?

PRM48 datasheet
https://www.vicorpower.com/documents/datasheets/PRM48JH480x250A02_ds.pdf

 

[d123]

Hi,

I have tried to understand the datasheet schematic and pins, and skim-read the descriptions further on in the document, and with my limited understanding, I'd have thought that it makes sense to power the EA from VAUX, as if the PRM is disabled, then the VTM is also not powered, so the load isn't powered either, and so presumably the EA would have nothing to compare and it's output signal would serve no purpose until the PRM is enabled again.
Sorry, treez, trying to help, if I haven't understood anything, my apologies.

 

[treez]

thanks, no i think you are very correct...the VAUX pin collapses i think deliberately whenever the module is disabled, because then the error amp gets no power and so its output will not rail high, so when the module comes back on again, the error amp output starts from low, which is the wanted and desirable situation....fo a slow and steady smooth startup with no overshoot.

Similarly, the current monitor is required to monitor current right from the startup when the prm48's output is 0v...therefore, this should ideally be a hall sensor...but does anybody know of a good "over the top opamp" for this purpose.....the hall sensors are all a little large at soic8 size and bigger.

 

[d123]

Hi,

I have no idea if these are suitable, or their price:

http://www.linear.com/product/LTC6101

http://www.linear.com/product/LT6105

Found this whilst browsing: "Current Sense Circuit Collection" - Linear Technology (soon to be incorporated into Analog Devices...). It's a 118 page app. note.

http://cds.linear.com/docs/en/application-note/an105fa.pdf

 

[treez]

thanks, ill look at that stuff, i know the LTC6101 wont be useful though as it gives no output till the rail its measuring the sense resistor on goes above 4v...and we need it to measure from 0v upwards.

 

[d123]

Okay, I see...

 

[asdf44]

Why not low side sensing?

 

[treez]

Thanks, we dont want to split up the ground plane.

 

[asdf44]

So then a highside/lowside current sense amp such as this (-14V to +80V common mode range):

https://www.digikey.com/product-detail/en/texas-instruments/INA282AIDR/296-27820-2-ND/2409368

Or this (-2 to 65V):
https://www.analog.com/media/en/technical-documentation/data-sheets/AD8211.pdf