Logic level shifters

[justin_t]

Hi

I am having a few issues when trying to select a logic voltage shifter for an application.

I am trying to interface a GPRS modem chip with Tera Term terminal program via RS232.

I have been looking at a Maxim MAX3386EIPWR chip, where it seems that the logic level is determined by the voltage applied to a pin VL. The data sheet references to 3.3V for the power supply and VL for the application circuit and recommends 2.25V minimum for VL.

My logic levels are 1.8V max. The VL absolute ratings are -0.3 to VCC+0.3.

Q should applying 1.8V to VL give me the logic levels I require?

Q If I apply 1.8 V to VL will I need to change capacitor values from the application circuit to suit?

If this chip is not suitable, has anyone came across a chip that will give 1.8V to RS232 logic voltage levels?

I have attached the transceiver data sheet and the logic levels of my modem chip for reference.

Thanks

Jusin

 

[ericgibbs]

hi,
The datasheet of the MAX3386 indicates a minimum of 2.5V logic, so I would say its not suitable.

Look at this link for options.
https://www.linear.com/products/rs232|rs562_transceivers

 

[Mr RB]

If you are after a quick solution then 1.8v logic levels will switch a NPN transistor just fine, and an NPN transistor will drive a PC serial port. Well, almost all PC serial ports that is.

 

[justin_t]

Mr RB, thanks but I would like to have a chip for the job as I need a long term soultion. Will keep that in mind for the future.

Thanks Eric, I was a bit confused as it was a chip that the modem manufacturer had recommended but I wasnt totally sold after reading the data sheet. Ill do another search. Ideally the component is in Farnell or RS for ease of purchase.

 

[crutschow]

A google search turned up this.

 

[ericgibbs]

A google search turned up this.

Carl,
I have already posted this link info the OP, post #2.

 

[crutschow]

Carl,
I have already posted this link info the OP, post #2.

You certainly did. Teach me not to look at the links.