Why is there no 6-pin USB to RS232 chip? - Page 1
Forum section: electronics / beginners

author: dusan
author_rank: Regular Contributor
timestamp: April 22, 2024, 02:13:21 pm
content: Why is there no 6-pin usb to RS232 chip?Code:THIS+------+ +------+ +-------+| |------|5V RX|-----| || | | | | || |------|D+ TX|-----| MCU || USB | | | | || CONN.|------|D- GND|--o--| || | +------+ | +-------+| |-----------------+------+I'd buy that for a dollar!

author: ataradov
author_rank: Super Contributor
timestamp: April 22, 2024, 02:51:17 pm
content: A couple reasons. First of all, most applications would want to use separate VDD for IO, since 5 V is not the most common voltage anymore. You can make such device take external regulated 3.3 V, but that again would limit VDDIO range.And then USB is 3.3 V signalling, so you would need some voltage regulator if you use 5 V supply. This regulator would likely need an external bypass capacitor.This is exactly what happens with Holtek HT42B534. It is available in 8-pin SOP package and two extra pins go to VDDIO and the bypass capacitor for the internal voltage regulator. This way this device can be used with system voltages 1.8-5.0 V.The annoying part with those devices is that they are not standard CDC ACM class, so they need proprietary drivers.

author: Kim Christensen
author_rank: Super Contributor
timestamp: April 22, 2024, 03:36:12 pm
content: Because RS232 also supports handshaking lines in addition to Rx and Tx. More economical to make one IC, which you sell a ton of, than to make a variety of lesser capable ones.

author: ataradov
author_rank: Super Contributor
timestamp: April 22, 2024, 03:39:22 pm
content: There are plenty of small pin count ICs that don't include any handshaking. Just not 6 pin ones. And they do have the same silicon internally, so it is just a matter of packaging.

author: pcprogrammer
author_rank: Super Contributor
timestamp: April 22, 2024, 06:54:48 pm
content: The smallest ones I know of are the CH340N which has a SOP-8 package and the CH340E which has a MSOP-10 package which is used on smallmodulesAliexpress sells.When it is about board size the MSOP-10 is the smallest one.

author: coppice
author_rank: Super Contributor
timestamp: April 22, 2024, 07:30:17 pm
content: Quote from: pcprogrammer on April 22, 2024, 06:54:48 pmThere are other SOP8 choices. Prolific, for example, make a couple of variants in that form factor.

author: magic
author_rank: Super Contributor
timestamp: April 22, 2024, 07:31:06 pm
content: Yep, PL2303SA is another one in SO8.Compatible clones (I doubt they are genuine) readily available on AliBay.Works out of the box on Linux.I have never seen 6 pins, though. The point about separate I/O voltage is very true - there is probably nothing with less than 7 pins.

author: magic
author_rank: Super Contributor
timestamp: April 22, 2024, 08:00:12 pm
content: Quote from: ataradov on April 22, 2024, 02:51:17 pmAs far as I see, HT42B534 datasheet states that this chip is CDC compatible.

author: ataradov
author_rank: Super Contributor
timestamp: April 22, 2024, 08:05:50 pm
content: Quote from: magic on April 22, 2024, 08:00:12 pmYeah, I confused them with CH340. The issue with Holtek is really spotty availability of the 8-pin version. I've got some in stock, but I'm reluctant to use them in new designs, since getting more would be hard.

author: MLXXXp
author_rank: Frequent Contributor
timestamp: April 22, 2024, 08:26:22 pm
content: Quote from: dusan on April 22, 2024, 02:13:21 pmDo you actually mean RS232 or just logic level UART? For RS232, TX and RX would have to output and accept positive andnegativeswings within RS232 specifications.

author: dusan
author_rank: Regular Contributor
timestamp: April 23, 2024, 06:21:03 am
content: I mean USB virtual com port to uart that is used by mcus like stm32