Hi,
We have made two designs with the LM25117. One to output 15 volts and one to output 4.5V. The basic specifications of both designs are as follows:
| Vout = 4.5V | Vout = 15V |
| Iout = 9A | Iout = 3A |
| Vin = 24V | Vin=24V |
The schematics of both designs are added at the bottom of this post. We made one PCB and tried both designs on it.
The design with 15V output works perfectly and has an efficiency around 96% depending on input voltage and output current.
The design with 4.5V output only has an efficiency around 82%. We tested it over a range of input voltages and output currents. Looking at the data from the evaluation kits and the electronic workbench the design should have an efficiency around 92%. We suspect there is an error in the component values we used to create the 4.5V design because the 15V design works flawlessly, but all the values we used for the 4.5V design are derived from the equations in the datasheet.
At this moment we are at a loss and are hoping we could get some pointers to get the efficiency from the 4.5V design up to appropriate levels. Many thanks in advance!
4.5V schematic:
15V schematic:
