[time-nuts] RS485/422/232 Chip
didier at cox.net
Sat Apr 26 09:19:06 EDT 2008
I am using the LTC1535 in an application right now, and if you need RS-485,
it is pretty neat. It includes the hardware to drive a small transformer
that will provide you with an isolated 5V floating supply too.
However, I am MUCH more impressed with the Analog Devices ADuM5241ARZ which
not only has two isolated digital channels, but also the power transformer
is built-in, and the whole device fits in an SO-8 package. You can get 5V at
10mA out of it. Analog calls this series "Digital Isolators"
This is absolutely truly amazing. I am using one in one of my products right
now. The Analog Device part is not RS-485 compatible, it is just a digital
isolator (TTL in, TTL out), but with the built-in 5V power supply, you can
drive any RS-485 driver. For RS-485, you will need the 4 port version of the
chip (for the Tx Enable)
The app note says it runs at 300 MHz. I have not checked the device with the
spectrum analyzer yet, but with a 100 MHz scope, I can't see anything.
They now have special versions for I2C and even a new one that provides
isolated gate drive to power MOSFETs.
Both devices are specified to sustain 2500VAC for one minute (UL
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Christian Vogel
> Sent: Saturday, April 26, 2008 5:17 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] RS485/422/232 Chip
> Hi Bruce,
> >> The MAXIM MAX3162E will do RS485/422 and RS232 in the one
> chip , get samples from maxim.com.
> > These devices only implement a single RS485/RS422
> transmitter and receiver.
> That's true for the 3160 which can be switched between two RX
> and two TX of RS232 or one RX and one TX of RS485.
> The 3162 does both functions simultaneously.
> I had a look at the MAX3535E recently, which has a isolated
> RS485 transceiver with capacitive coupling in it, did anyone
> of you use those to break ground-loops? I'm especially
> interested if this kind of "capacitor-isolation barrier" adds
> any significant noise to the RS485 lines, which might couple
> into sensitive signals running in parallel, or if I should
> just go the traditional optocoupler-route.
> Greetings from Germany,
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