I have designed a DC-DC converter using MP4575 with below requirement:
Input voltage range: 9V to 36VDC
Output voltage: 7.5VDC/3A
Input source is from a battery.
I have doubt on input and output capacitor selections as theoretically based on calculation we get less ripple voltage but practically it is more.
Also we would be designing it on 2 layer PCB.
Request you to go through the circuit sketch I have attached here and let me know improvements.
Hi Manjesh, welcome to the forum!
Since you are concerned about the output ripple, you can increase Cout to 2x 47uF instead of 22uF.
For your comp network, with a 15k Rcomp, set C3 from Rcomp to GND somewhere > 2nF. The value of C4 in parallel with Rcomp and C3 depends on the ESR of your output caps.
EN should be pulled high or low, so you should probably depopulate the 22k Rdown. You can connect EN to some additional circuitry to pull the pin down to disable it if necessary.
I think the rest of the application looks fine. If the duty cycle is consistently high and you’re operating on the lower end of your Vin range, you might consider a BST diode as well.
Thanks for your quick reply !
I have concerns, regarding BST diode as there might be a case, where we will be operating at lower VIN range as input source is a battery which will drop to lower side of input voltage range i.e 9VDC.
Since input voltage range to BST pin is 3V-5V rail and this entire dc-dc module is a standalone circuit in our design we do not have external voltage source of 3-5VDC to apply at BST via diode as output is set to 7.5VDC.
What will be the case at VOUT here in absence of BST diode during higher duty cycle ??
It’s possible it will affect your converter efficiency at higher duty cycles, since there’s less time available to charge the BST cap.
