DPS5015 high-side current sense

[kilowatt21]

Hi,

i want to use DPS5015 in my project but high-side current sensing is a must for me. i tried to find schematics for the power supply but wasn't able to. So half a day later i have a crude schematic of it. it's not complete in any way, but the main switching and controlling components is there.
first i disconnected the low side sensing feedback line from R6 and to it feed high side current sensing from INA169.  because i changed the current/voltage ratio i also changed set current circuit by removing R10 and feeding my set current voltage to lifted R8.

i tried using INA169 and LT1999 bouth of those chips does not work well, very unstable.
i think i'll have do something with R21, C7, C8..

if you see any errors in schematic please let me know. Any input towards high-side current solution is welcome.
i'm only a beginner  in these so please go light on me.

Thanks!

[Zero999]

I haven't looked at the schematics in great detail, but it's no surprise your changes have caused instability. Adding an extra current sense circuit will introduce an additional phase shift into the system, which can cause oscillation, as can adjusting the current/voltage ratio, which will alter the gain. Making any changes to the current loop, will require the frequency compensation network to be modified too.

[plazma]

One guy added external sense connectors. I have to ask for details.

[glarsson]

What is drawn in the "Gross Overcurrent Protection" box does not make sense.

[kilowatt21]

jop, that's because i had no luck searching for smd device marking, so i just put in whatever was used before. i think it's just different pinout op amp or something.

[kilowatt21]

Thanks for the reply.

Today i tried TLV172 (10MHz op amp) with pnp transistor and is seems to be fast enough so that existing circuitry does not need "any" modification. But if i want to use a device with good CMRR i guess i'll have to figure out how to implement much slower current sense devices.
I'll try looking into frequency compensation.

any input on that is welcome.

Thank you.

[glarsson]

Still doesn't make sense. You have one output (the transistor) and one input (from sense). The function between should be a comparator comparing the tension from the sense resistor with a threshold. This threshold is probably the junction between the R001 and R002 resistors. R001 is likely not drawn correctly.

[kilowatt21]

Hi,

thanks for for spotting that. I traced the tracks again, made so measurements and updated the circuit.

I'm still learning about the magic of frequency compensation....   
if i'm understanding correctly, the idea is to slow down the control side of circuitry so that there would not be any over-compensation because of the delay in feedback circuitry? In this device the voltage control is quite fast so frequency compensation does not have to limit the compensation that much. Current feedback is way slower so the frequency compensation has to slow the compensation way down so that current feedback would have time to react to the changes that goes on in the power side of things.

Am i thinking in the right way?

Thanks.