USB to TTL IC recomendations

[anishkgt]

This will clarify

https://www.silabs.com/documents/public/user-guides/CP2102-EK.pdf

was not helpful as it is specifically for USB powered.

[anishkgt]

would this be correct.

[Monkeh]

No.

Read the datasheet. All of it.

[anishkgt]

was expecting something better than a 'NO' like where exactly.

[Monkeh]

Well for starters you're going to blow the chip up by shoving 5V into the rail indicated to be 4.2V absolute max..

VBus should not be tied high. See datasheet, page 20.

[anishkgt]

Thanks but, Page 20 was all about Functional description. Going through the datasheet with a cup of coffee, came out with the one attached.

[Monkeh]

Thanks but, Page 20 was all about Functional description.

Please make sure you're reading the current datasheet, then: https://www.silabs.com/documents/public/data-sheets/CP2102-9.pdf

Going through the datasheet with a cup of coffee, came out with the one attached.

We're getting somewhere.

Now the self-help is out of the way:

Your Vbus divider will exceed input specs at 5.5V in. Probably not a big concern, but I'd go for 22k over 33k.
The 4.7? cap on +5V isn't really needed, but per-datasheet a 1? ceramic should be there. Realistically, you're fine with 100n on both Regin and Vdd.

Your LEDs are never going to light. You may want to look at other chips in the Silabs range (CP2102N, CP2104) which have programmable I/O, including dedicated LED drive functions.

Showstopper: You're never going to come out of reset.

Oh, and where'd the third ground pin come from?

[anishkgt]

Your Vbus divider will exceed input specs at 5.5V in. Probably not a big concern, but I'd go for 22k over 33k.

i could be wrong with the parameters on LTSpice but i see 3.4v. How true is that ?

Your LEDs are never going to light. You may want to look at other chips in the Silabs range (CP2102N, CP2104) which have programmable I/O, including dedicated LED drive functions.

I was following this from digikey https://www.silabs.com/documents/public/data-sheets/cp2102n-datasheet.pdf and their the TX and RX leds are connected to TX and RX pin of the CP2102N on Pg:18

Showstopper: You're never going to come out of reset.

change to VDD from GND

Oh, and where'd the third ground pin come from?

Which third GND?

[anishkgt]

I was working with the wrong package in eagle. The one that eagle has is the MLP28 and i was following the QFN28 datasheet.

[Nusa]

VBUS looks like a 5V input (abs max 5.8V). Why the voltage divider?

[anishkgt]

VBUS looks like a 5V input (abs max 5.8V). Why the voltage divider?

to ensure reliable device operation, pg:5

[anishkgt]

made an eagle QFN28 Package and a symbol.

[anishkgt]

replacing 22k and 47k with 33k and 22k respectively gives 2.00v
Just adding LEDs on the RXT and TXT pins would make it glow or should the IC be programmed in any way ?

[eugenenine]

You have the Microchip part too, the MCP2200.
About $1.50.

I thought this one myself but it appears to need some setup to use.  I couldn't find anywhere that didn't require some silly windows program to set the baud rate and such.  I ended up going back to the FTDI since I don't run windows anyway I don't have driver issues.

[Peabody]

I just want to reinforce what's done with the /RST pin on the CP2102.  I ran across a batch of USB-to-TTL modules using this chip, and unfortunately all the outputs - DTR, RTS and TXD - were at about 4.3V instead of the correct 3.3V, which might easily destroy a 3.3V processor.  It turned out that it was because the designer had connected /RST to VBUS (5V).  One of the drawings above showed it connected that way, and that's a no go.  VDD yes, but not VBUS.  Actually, it will run fine if you don't connect /RST to anything.

Anyone needing to add this function might want to look at using a module instead of the chip and all the supporting parts.  The one I used had a micro USB connector already installed, and sells for $1.23, which is less than what I would have paid for the chip alone.  The modules I got here have /RST as NC, which works fine:

https://www.ebay.com/itm/162217753561

[anishkgt]

It turned out that it was because the designer had connected /RST to VBUS (5V).  One of the drawings above showed it connected that way, and that's a no go.

The RST pin if grounded would be in reset state would never come out of it hence the same is connected to +5v and not VBUS. VBUS is connected to a voltage divider. The schematic is self-powered and not VBUS powered. At least that is what i intent to do it.

I will wait for the pros to have a look at it.

[Monkeh]

i could be wrong with the parameters on LTSpice but i see 3.4v. How true is that ?

Because you just ran it with a 5V input, not a 5.5V input. And seriously, LTSpice for a divider?

replacing 22k and 47k with 33k and 22k respectively gives 2.00v

Other way around..

Just adding LEDs on the RXT and TXT pins would make it glow or should the IC be programmed in any way ?

Read the datasheet! Pages 15 and 18.

Why are your 100n caps polarized?

[jdgabbard]

I've used the CH340 without any problems.  I actually needed a USB to TTL adapter the other day and wired one up in about 10 minutes.  It's a good option.  The only catch is that you need a 12mhz oscillator/crystal. 

[ebclr]

CH340 is nice but have some little problems.

Windows Driver interface is very unusual and ugly,
When new ms release new windows versions, drivers take a long time to be updated while CP2102 coming in beta test stage
requires a crystal, that cp2102 does not
It's bigger in size than CP2102

Other than that CH340 works nice

[anishkgt]

Why are your 100n caps polarized?

those are US model caps and they are ceramic, polarised has a '+'

Read the datasheet! Pages 15 and 18.

The page says
By default, all of the GPIO pins are configured as a GPIO input. The speed of reading and writing the GPIO pins is subject to the timing
of the USB bus. GPIO pins configured as inputs or outputs are not recommended for real-time signaling.
More information regarding the configuration of these pins can be found in Xpress Configurator in Simplicity Studio and AN721: CP21xx
Device Customization Guide. Guidance on GPIO usage can be found in AN223: Runtime GPIO Control for CP210x.
Link to the guide https://www.silabs.com/documents/public/application-notes/AN721.pdf

well in that case i'd rather go with CH340.

[anishkgt]

@cdev how is the GPIO's configured to blink the TX and RX LEDs

[Monkeh]

Read the datasheet! Pages 15 and 18.

The page says
By default, all of the GPIO pins are configured as a GPIO input. The speed of reading and writing the GPIO pins is subject to the timing
of the USB bus. GPIO pins configured as inputs or outputs are not recommended for real-time signaling.
More information regarding the configuration of these pins can be found in Xpress Configurator in Simplicity Studio and AN721: CP21xx
Device Customization Guide. Guidance on GPIO usage can be found in AN223: Runtime GPIO Control for CP210x.
Link to the guide https://www.silabs.com/documents/public/application-notes/AN721.pdf

well in that case i'd rather go with CH340.

That's up to you. It only takes a moment to configure and you get custom serial numbers as a free bonus.

Please read page 18 as well.

[anishkgt]

Yup that sure is an advantage and that’s why I would give it a try.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D

[anishkgt]

Oh just thought i'd share as i was a bit confused. There are two models of the same one is CP2102 and one with the 'N' at the end which is the new one which is USD1.4 and CP2102 is USD3.00.

My design and all questions were about the CP2102N and so are my schematic. With that cleared would the attached be correct following this datasheet https://www.silabs.com/documents/public/data-sheets/cp2102n-datasheet.pdf

Just a few questions about the schematic.
Are the leds connected on pins 18 and 19 correct and is there 4.7uf polarized cap required ?
Can this be connected to the VREGIN on pin 7.

[Monkeh]

The LEDs should work now, yes.

You'll survive without the extra cap.

Your divider is still the wrong way around.

Once again, where is the third ground pin coming from?