USB-C charge IC compatible with USB 2.0 inrush specs - Page 1
Forum section: electronics / projects

author: huub8
author_rank: Contributor
timestamp: February 26, 2020, 03:02:22 pm
content: Hi all,I'm working on a design that in which I would like to use a one cell 3000 or 4000mAh li-ion battery. I would like to charge this battery over the same usb connection that I'll be using for serial communication with my microcontroller (using an onboard serial converter). The absolute worst-case peak load of the microcontroller and the peripherals is 1.5A at 5V (although it will normally be much less).Since the device needs to run off the usb port even when the battery is dead, USB-C with its 1.5A of current in the default profile seems to be perfect. This would offer me enough current to both charge the battery and run my system at the same time.However, I would still like to be able to charge it (slowly) using regular USB 2.0. I would love to use one IC to charge the battery and power the system (so some kind of power path management), utilizing the USB-C current when possible but respecting the 500mA usb 2.0 inrush spec when connected to a usb 2.0 port.So basically I'm looking for an IC (or it that doesn't exist another nice way too):Utilize the 1.5A of USB-C when present to charge the battery while maintaining stable power to the system (automatic power management of load/battery)While adhering to the USB 2.0 spec of 500mAh when connected to a USB 2.0 port to charge the battery (/limit the discharge of the battery when the system is being used)Thanks!

author: David Hess
author_rank: Super Contributor
timestamp: February 27, 2020, 07:40:22 pm
content: The only examples I quickly found used separate USB power negotiator and lithium battery charging controllers with a signal to the later to indicate maximum available current.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 28, 2020, 12:28:04 am
content: Check the voltage at the pulldowns. The Type C spec actually lists what voltages to expect with different inputs.

author: huub8
author_rank: Contributor
timestamp: February 28, 2020, 09:13:03 am
content: Thanks for looking into it David!To me it seems like this is a common circuit to want (basically any rechargeable device that works with USB-C would also be expected to work with USB 2.0). But I couldn't find any either.Quote from: David Hess on February 27, 2020, 07:40:22 pmI can't really do that since it would require a powered system to do that with my microcontroller. I could of course create some circuit for this, but that is exactly what I'm trying to find in the form of a chip.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 28, 2020, 01:31:26 pm
content: You put a pair of 5.1k pulldowns in your device and the cable pulls it up with a resistor value that depends on how much current is available. Then you use a comparator to distinguish between them.https://community.cypress.com/docs/DOC-10779

author: David Hess
author_rank: Super Contributor
timestamp: February 28, 2020, 08:42:02 pm
content: Quote from: huub8 on February 28, 2020, 09:13:03 amI thought so also which is why I looked. It would be a handy thing to have for simple projects to charge off of USB.QuoteNo, I mean there are ICs which negotiate power delivery while passing the USB signals onto the USB controller and also provide some other outputs which indicate how much current is available. So it would be a two IC solution without a separate USB controller or processor.