Hi, I am using MP2338 to cover a wide input voltage between 5V to 20V and give output of 5V/3A. I designed the circuit based on the reference schematic in datasheet but when i apply 5V input to the circuit I get 4.7V at the output. Why this dropout occurs ? What can I do to get 5V output when I apply 5V input ?
The circuit in the datasheet works from 6.5V, did you try 6.5V in? Why do you suppose they said 6.5? You need a part with better dropout performance. What is biting you in the minimum OFF time of 150nsec which means Vout will always be lower than Vin. I believe MPS makes parts with better dropout performance than this one, but not sure how to search for it. Have you tried the forums?
Thanks for the reply. In the datasheet it also says “Wide 4.5V to 28V Operating Input Range”, thats why I chose this part actually. When I try 9V input for example, no problem I get 5V but when the input falls down to 5V, I get 4.7V in the output. What should I do ?
You need to start dancing, 5V really can be as low as 4.75 and be in spec (perhaps) The obseved dropout is 0.3V so this “works” down to 5.05V in in the sense that you get adequate output voltage.
Alternatively you need to find a part with better dropout performance.
MP8715 touts a 100% duty cycle capability. That should do the trick, get a demo board first
Thanks for the answer, this could be a solution for me.
It says “Most of the internal circuitries are powered from the 5.1V internal regulator. This regulator takes the VIN input and operates in the full VIN range. When VIN is greater than 5.1V, the output of the regulator is in full regulation. When VIN is lower than 5.1V, the output decreases, a 0.1uF ceramic capacitor for decoupling purpose is required.” in MP8715 datasheet. This could be tricky for 5V input case
well they say it operates to 4.5V which I have to think means that the bandgap stays within spec. The internal UVLO on the falling input voltage looks like it is in the 3’s. Play with the demo board
Thanks, MP8715 seems like a better solution. Do you think I have problems if I switch MP2338 with MP8715 ? My design works mainly with 9V input and 5V/2.5A output
No idea, isn’t the pinout different? If the 5V spec is BS then sure doing nothing strikes me as the attractive option. If you are paid by the hour then you have no choice but to redesign. This is a engineering management decision made between you, your boss and her boss, the customer, marketing… Offer both solutions, sit back and let them decide after the routing thumping of chests and flinging of feces.
Yep pinout different so I cant just replace MP2338 with MP8715 but I can design a new circuit for it.
I would try to get a demo board to double check it is adequate for your application, but that is just me