Monolithic Power DC/DC Converter MP2359 - Page 1
Forum section: electronics / projects

author: fossil
author_rank: Contributor
timestamp: January 31, 2019, 01:56:16 am
content: I am newbie and trying to design a dc/dc power supply.Here is a dc/dc converter design for a custom ESP8266 board. The design is based on Monolithic Power Systems MP2359 with 4.5V to 24V input voltage range. The output voltage is 3V3. The reason to choose DC/DC converter instead of an LDO is to provide at least 250mA to any add on board.The minimum input 4.5 voltage for MP2359 is too close to input voltage 5V coming from USB port / mobile charger. The minimum input voltage of MP2359 is well below any droop on input.The attached circuit is based on reference design in datasheet for <5V input voltage. Is there anything else I can do to improve the stability of power supply?Edit: Updated the schematic

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 31, 2019, 03:58:07 pm
content: What about stability? Like getting desired output (250mA) at lower input (under 4.5V)? Pick a different chip.Tim

author: fossil
author_rank: Contributor
timestamp: February 01, 2019, 05:14:44 am
content: Quote from: T3sl4co1l on January 31, 2019, 03:58:07 pmI guess the minimum voltage is too close to input. Will select a different chip.

author: mariush
author_rank: Super Contributor
timestamp: February 01, 2019, 05:39:42 am
content: Just use something else, like for example :AOZ1280 (3.6v min, 26v max, cheap... 60 cents at 25qty, 30 cents at 1k) :https://www.digikey.com/product-detail/en/alpha-omega-semiconductor-inc/AOZ1280CI/785-1277-1-ND/2769845^ however be aware that max duty cycle is 87% so you'll need at least 4.2v to get 3.3v stable ... still you should get at least 4.2v from usb, so it should be fine. it's worth knowing if you want to use a lithium (3.7..4.2v battery), you wouldn't get 3.3v quite right.Richtek RT7294C (max 18v in, but 4.3v min, synchronous rectifier so you save on separate diode) :https://www.digikey.com/product-detail/en/richtek-usa-inc/RT7294CGJ6F/1028-1507-1-ND/5724414RT8299ZQW for 3v..24v in, synchronous :https://www.digikey.com/product-detail/en/richtek-usa-inc/RT8299ZQW/1028-1158-1-ND/3078161

author: fossil
author_rank: Contributor
timestamp: February 01, 2019, 11:25:10 am
content: Quote from: mariush on February 01, 2019, 05:39:42 amI had almost decided to use AOZ1280, but later switched to MP2359. I was lazy and wanted to avoid the math needed to design AOZ1280 for 3.3V. MP2359 offered a ready reference design. I will revisit AOZ1280.Quote from: mariush on February 01, 2019, 05:39:42 amI am looking for switching frequency of 1.4MHz or more.Thanks for pointing me to AOZ1280

author: Yansi
author_rank: Super Contributor
timestamp: February 01, 2019, 11:28:06 am
content: Then use AOZ1282CI-1.Or some other crazy LT part. But I do not think there is much point in chasing MHz, if you are a newbie SMPS designer.//EDIT: Mistake, I thought the AOZ1282CI-1 had more MHz :-/

author: mariush
author_rank: Super Contributor
timestamp: February 01, 2019, 01:53:40 pm
content: Quote from: fossil on February 01, 2019, 11:25:10 amShouldn't make your decisions on frequency alone, 500kHz is already quite high. You'll need slightly bigger inductors, but they'll still be reasonably small and cheap. The benefit is it's a sync rectifier, so you save some money and pcb space by not having to use a diode... so it works out in the end.In the case of the first Richtek part, it's also a TSOT-23-6 part, and you may be able to find chips with same pinout... for example I think MP2451 would work :https://www.digikey.com/product-detail/en/monolithic-power-systems-inc/MP2451DJ-LF-Z/1589-1893-2-ND/9555317(but obviously different inductor would have to be used as this is a 2mhz part). You'd need to add a diode footprint in that case, as this MP2451 is non synchronous rectifier.It could also work with 700kHz RT8258 which has same pinout but being non syncronous rectifier would need a diode (you can have the footprint on board and just not populate it if you use the sync rectifier version) :https://www.digikey.com/product-detail/en/richtek-usa-inc/RT8258GJ6/1028-1044-2-ND/2546043

author: fossil
author_rank: Contributor
timestamp: February 01, 2019, 02:34:12 pm
content: Quote from: mariush on February 01, 2019, 01:53:40 pmI think, as suggested by you, AOZ1280 is pretty good choice. AOZ1280's frequency is 1.5MHz and inexpensive. I will go with it.

author: fossil
author_rank: Contributor
timestamp: February 01, 2019, 03:34:45 pm
content: Quote from: mariush on February 01, 2019, 01:53:40 pmThanks for the suggestion. I never thought in that angle of using different parts with same pin out. I can use the same board with different input voltages and/or probably different power budget within reason.