3.3v powersupply not stable

[aliyesami]

I have built a powersupply for my microcontroller unit using
LM2575HV_3.3V but voltage is not stable. I am using it with the Meanwell LDD 770H 50v driver . If there is no load on the driver I get the voltage out put as 3.40 volts and if the driver is loaded the output voltage drops to 2.90 volts.
the chip spec is 3.3v so I am not sure how its producing 3.40 volts.
I have constructed the circuit as per datasheet specs

 

[dick_freebird]

You could begin with seeing whether the load regulation
as-seen, is as-spec'd. If not then I'd start with ground
integrity (you do not say about "driver" current or how
it is returned).

LDOs often have a minimum current especially if simple
PMOS outputs; leakage current needs somewhere to
go if the error amp is to have authority.

3.40V is about 2% error, not terrible. The 2.90V, either
you are overcurrent on the output or the "driver" is
pushing local reference ground voltage up by a couple
tens of mV, and dropping the setpoint.

Datasheet schematics are fine as a start, but often
the layout art is not communicated in that material.