USB-to-TTL

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turboscrew
Posts: 51
Joined: Fri Mar 10, 2017 7:36 pm

USB-to-TTL

Post by turboscrew » Thu Aug 10, 2017 2:14 pm

I bought some of these lately (well, different seller, but YP-01 on the bottom anyway).
https://www.aliexpress.com/item/PL2303- ... .57.OiruJX
It says "500mA self recovery fuse for protection". Which overcurrent? I didn't see a mention of that in the PL2303HX data sheets.
It seems to have genuine PL2303HX - telling by the driver and Prolific checker program.
The seller's page has changed (YP-01 to D-SUN), but the original page had pretty much this text:
Features:
Adopt imported controller RS232 TTL,which can stabilize the flash with high speed
500mA self recovery fuse for protection
Two data transmission indicator can monitor data transfer status in real time
Reserve 3.3V and 5V pin interface,easy for the DDWRT of different voltage system that need power
The entire board is coated by high quality transparent heat-shrinkable sleeve,making the PCB in insulation state from outside,
so that the board won\'t burnt down by material short cut.
Electrostatic package,insures the board will not be damaged before use
Support WIN7 system
Also, how much current do I dare to draw from the 3.3V pin?
The PL3203HX data sheets specify 150 mA, but somewhere else there was some talk that one can draw nearly 400 mA, but the voltage drops to 3.0V.

And has anyone come up with a good explanation, why even the basic numbers - like what's the RxD/TxD-levels are not usually mentioned on the sellers' pages?

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Pito
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Re: USB-to-TTL

Post by Pito » Thu Aug 10, 2017 4:06 pm

The over-current fuse is not related to PL2303, but generally it is about protection of the +5V rail which is available at the pin header.
The Rx/Tx pins are 3.3V level.
The PL2303HX takes typically 20mA.
I did not find the max output current for the internal 3.3V regulator (VO_33) in the datasheet, but I would not recommend more than 5-10mA (I would not use it for powering the BluePIll or MMini).
The PL3203HX data sheets specify 150 mA, but somewhere else there was some talk that one can draw nearly 400 mA, but the voltage drops to 3.0V.
Can you point us where it specifies 150mA??
Imagine you take 0.4A off the 3.3V internal regulator.
The power loss at the regulator would be
P = (5V - 3V) * 0.4A = 0.8W
With that package the chip will smoke.
Pukao Hats Cleaning Services Ltd.

turboscrew
Posts: 51
Joined: Fri Mar 10, 2017 7:36 pm

Re: USB-to-TTL

Post by turboscrew » Thu Aug 10, 2017 7:29 pm

Thanks!

Not all the data sheet versions seem to have mentioned the internal regulator current, but this has:
http://www.usconverters.com/downloads/d ... pl2303.pdf Page 15.

And there someone has done some research. Note that he doesn't say the chip survives the 400 mA. :lol:
http://nerdralph.blogspot.fi/2015/02/pl ... utput.html
Just wondered if anyone here has more real-world experience...

Also found this - even if it's for NXP's chips.
I guess the Rth(j-a) doesn't differ that much from manufacturer to manufacturer...
Their SSOP28 has Rth(j-a) about 115 K/W with 2.5 mm2 die size... That would mean that in 30C ambient temperature the junction
temperature would be 122C. No idea of the die size of pl3203, though. :lol:
http://www.nxp.com/downloads/en/thermal ... PTER_6.pdf
(That link may be useful to others too...)

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