Why is there no 6-pin USB to RS232 chip?

[dusan]

Why is there no 6-pin usb to RS232 chip?

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                THIS               
+------+      +------+     +-------+
|      |------|5V  RX|-----|       |
|      |      |      |     |       |
|      |------|D+  TX|-----|  MCU  |
| USB  |      |      |     |       |
| CONN.|------|D- GND|--o--|       |
|      |      +------+  |  +-------+
|      |-----------------           
+------+                         

I'd buy that for a dollar!

[ataradov]

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.

[Kim Christensen]

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.

[ataradov]

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.

[pcprogrammer]

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 small modules Aliexpress sells.

When it is about board size the MSOP-10 is the smallest one.

[coppice]

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 small modules Aliexpress sells.

When it is about board size the MSOP-10 is the smallest one.

There are other SOP8 choices. Prolific, for example, make a couple of variants in that form factor.

[magic]

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.

[magic]

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.

As far as I see, HT42B534 datasheet states that this chip is CDC compatible.

[ataradov]

As far as I see, HT42B534 datasheet states that this chip is CDC compatible.

Yeah, 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.

[MLXXXp]

Why is there no 6-pin usb to RS232 chip?

Do you actually mean RS232 or just logic level UART? For RS232, TX and RX would have to output and accept positive and negative swings within RS232 specifications.

[dusan]

I mean USB virtual com port to uart that is used by mcus like stm32