Getting clean 5V out of USB VBUS with DC/DC Converter - Page 1
Forum section: electronics / beginners

author: HasanSyr
author_rank: Contributor
timestamp: March 14, 2025, 08:53:46 am
content: I'm designing an FPGA development board around a SOM. The SOM requires 5V@3A and generates the rest of the voltages by itself with the MP2143DJ buck converters. There is also 3.3V needed on the dev board for peripherals, Im going to use TLV62130A for that.The issue is that VBUS can range from 4.5V to 5.5V + cable/load losses. I was going to use another TLV62130A but that is a buck converter so in the case of VBUS < 5V it is not ideal.There is TPS6302x (see section 8.1) which is buck-boost and capable of stabilizing the voltage around the voltage, however, the max output current is 2A in boost mode. There is a document called "Using Non-Inverting Buck-Boost Converter for Voltage Stabilization" for this IC but it doesn't mention the max current however all the graphs show the current going up to 2A.Finally, there is TPS61022 (see section 8.3) which specifically an example for stabilizing voltage, however, it mentions that the range is 4.5V-5.25V when it's actually 4.5V-5.5V and since this is boost converter Im unsure if it will be able to buck the excess. Maybe the MP2143DJ can handle the bucking? Its input range is 2.5V-5.5V.In short:TLV62130A is a buck converter and might not be able to stabilize the voltage if VBUS < 5V.TPS6302x might not be able to supply 3A.TPS61022 is a boost converter and might not be able to stabilize the voltage if VBUS > 5V.

author: PGPG
author_rank: Frequent Contributor
timestamp: March 14, 2025, 09:30:07 am
content: I don't know all modern USB specifications but standard was that you can get from 5V USB:0.5A if connected to PC or hub having its own supply,0.1A if connected to hub having no its own supply.May be the current from 5V was increased in never USB standards but most power increase was get by increasing the USB voltage.

author: HasanSyr
author_rank: Contributor
timestamp: March 14, 2025, 09:43:16 am
content: Quote from: PGPG on March 14, 2025, 09:30:07 amIm using a USB-C 2.0 connector with 5.1k resistors on the CC lines

author: xvr
author_rank: Frequent Contributor
timestamp: March 14, 2025, 11:04:10 am
content: MP2143DJ has operating voltage range 2.5-5.5V (maximum absolute rating is 6.0V). So you can power it directly from USB without any additional processing.QuoteThis is not enough to get 3A from USB-C. You need to implement PD and negotiate the required maximum current from the power supply. There is no guarantee to get 3A without PD, it all depends on the power supply. A smart one can disconnect the load, a stupid one can burn out itself (or provide 3A - if you're lucky)

author: eleguy
author_rank: Regular Contributor
timestamp: March 14, 2025, 11:15:31 am
content: Add a PD sink controller in your design. For example AP33771C (PD3.1) is not too expensive and is pretty straight forward to use. One can ask the chip to negotiate voltage/current just with the resistors only. With AP33711C you can set the output (your board input) from 5V to 28V / 1A to 5A as long the host/charger/adapter supports it.HUSB237 could work as well (costs $0.19). However, there you cannot set the current explicitly. So, I am not sure how it works. Does it always ask the maximum available? HUSB238 is bit more expensive ($0.62) but it has both current and voltage settings.

author: PGPG
author_rank: Frequent Contributor
timestamp: March 14, 2025, 08:07:48 pm
content: Quote from: HasanSyr on March 14, 2025, 09:43:16 amI don't know what SOM is and I have never used FPGA but I don't see in your post the information about power source you use. You tell what you need to get but nothing about power source and everything depends on the power source in use.If you get 5V/5A power supply and connect directly to USB-A socked and then use USB-A to USB-C cable you will be able to get 5A from it regardless of having 5k1 resistors or not (provided cable will not get in fire).But if using USB-A to USB-C cable you connect your device to standard USB-A socket in PC than even having 5k1 resistors you will be not allowed (and in many cases not able) to get more than 0.5A.If you were not having these 5k1 resistors and connect with USB-C to USB-C cable to PC you will get 0V supply. Thanks to these resistors you will get 5V that is enough to start negotiation for more power.I have designed some USB devices but none of them consumes more than 50mA so I never thought about any limits and know nothing about it.

author: bson
author_rank: Unknown
timestamp: March 14, 2025, 08:17:26 pm
content: USB-PD is indeed the way to go. Negotiate a higher voltage and buck that to 5V, 3.3V, and anything else you need.