Using FT230X For Serial Comms and Battery charging - Page 1
Forum section: electronics / projects

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: July 07, 2017, 11:10:59 am
content: I have a circuit built that uses an FT230X. I’ve included a portion of the schematic in the picture below which is based on the USB-powered version that’s in the FT230X datasheet.My design uses a small 240 mAHr battery that’s charged at 240 mA from the +5V USB rail via a dedicated charge controller IC. A separate regulator (not shown) generates the +1V8 from the battery but this can be totally switched off to isolate the battery to prevent drain -in other words, I envision situations where the +1V8 is off but I'd still like to be able to charge the battery from USB. I’ve programmed the FT230X via the FT Prog utility to use CBUS3 as PWREN# and set max current draw to 300 mA. What I find is that, unless the +1V8 rail is live, I never get the PWREN# to go low and switch the Vbus through to my +5V USB rail; this means that +1V8 has to be switched on to charge. Questions:1. Is there any way to connect or set option in the FT230X to allow battery charging (i.e. send Cbus3 low) without the VccIO being live? This seems unlikely given that the FT230X's RESET# is connected to the +1V8 rail2. If I switch the battery-powered circuit on (make VccIO live) then the system works as planned but when will the PWNREN# be low? Will it be low when I’m plugged in for data exchange purposes and will it also be low if I plug the USB port into a charger? I don’t fully understand when PWREN# goes active low.3. Do Ihaveto run the Vbus through a switch rather than just connect it directly the input to the charge controller? I think I do but the USB rules/logic have me confused.Thanks in advance.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 08, 2017, 04:54:01 am
content: Keep it simple and power the charger direct from the USB. Many commercial products work that way.

author: jbb
author_rank: Super Contributor
timestamp: July 08, 2017, 06:54:58 am
content: Possible solution:Use the FT230 inbuilt 3V3 regulator to supply Vcc IO. Tie FT230 reset to 3V3. Then use nPWREN to control the charger enable. Add level translator to get UART signals from FT230 to 1V8 logic.Note the FT230 has no mechanism to measure or limit current. If you're enumerating as a 300mA device, you charger will need to limit its input current to say 295mA (the FT230 consumes approx. 3mA). Also, He charged current limit will have finite accuracy, so you might need to derate by 10% to a setting of 270mA.Aargh autocorrect is killing me!

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: July 09, 2017, 12:09:17 pm
content: Thanks for the suggestions, I like the simple idea that I remove Q1 and simply have the 5V feed to my charger IC be a direct connection to the Vbus; the charger IC is a BQ25100AYFPR which I believe will limit the current drawn so it should never draw more than say 300 mA and I think all USB ports are supposed to be able to supply 500 mA, right?Adding level translation means adding another chip so I don't see that as a good choice, I have been tasked with making the desig smaller for the next Rev - I think what I'll do to one of my prototypes (for a test) is remove Q1 and put a 0 Ohm resistor across D-S of the SOT23 pad so that Vbus is passed straight through to the charger IC.