24V supply voltage not working: SOLUTION
Finally, a solution was found for the power supply. The main problems was a bad soldered resistor in the feedback loop, upon a change in the board after the reception from DEM. Due to this the output was not controlled. It must be remarked that it was a not a DEM issue, but a badly hand-soldered resistor.
Then, after carefully checking the design (against the calculations provided by TI in its datasheet and SwitcherPro Desktop for checking the gain and phase margin) some modifications are submitted for an improved control of the 24V rail:
DESIGN VALUES**
Switching Frecuency: 475Khz
Crossover Frecuency: 23.75KHz
Vin : 12V
Vout : 24V
Feedback network*
> Rhigh: 50K
> Rlow: 1K51
Compensation network*
> Rcomp: 13K35
> Ccomp: 4.7uF
> Cpole: 68uF (upto 100uF)
RC network*
> Rrc: 335K
> Crc: 100pF
CHANGES IN COMPONENTS**
Rhigh R231, R232, R233, R234, R235*
> R231: not changed (10K)
> R232: not changed (10K)
> R233: not changed (10K)
> R235: not changed (10K)
> R234: 4K7 -> 10K
Rlow R229, R230*
> R229: 100 -> 510R
> R230: 4K7 -> 1K
Rcomp R254, R255, R256, R257, R258*
> R254: 10K -> 4K7
> R255: 10K -> 4K7
> R256: 10K -> 1K
> R257: 10K -> 100R
> R258: not changed (10K)
Ccomp C45*
> C45: not changed (4.7uF)
Cpole C190, C191*
> C190: 100pF -> removed
> C191: 100pF -> 68pF (100pF can be used, as well)
Rrc R261, R262, R263*
> R261: 470K -> 100K
> R262: not changed (470K)
> R263: not changed (470K)
Crc C196*
> C196: not changed (100pF)
Risns R259*
> R259 100R -> 1K
Output ceramic capacitors C189, C192, C193*
> C192: removed
> C193: removed
> C189: removed
With these changes, improved control is achieved and 24V are gotten from the 12V VME pin.