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Interface device for AD7762 (3.3V to 2.5V) and output current in digitals I/O

Question asked by werty on Jul 2, 2018
Latest reply on Jul 5, 2018 by werty

Hello,
I need an interface to use the AD7762 (2.5V logic) with a DSP (3.3V logic). The level translator must be bidirectional since the parallel bus is bidirectional.

 

The only thing I see is the ADG3308 but there are a couple of problems:

 

The first one is with voltage levels:

The AD7762 has an output level of 1.5V to 400uA and the ADG3308 needs a minimum input value of 0.65 × VCCA = 1.625V (VCCA = 2.5V) This does not work and it occurs to me if I can reduce the voltage VCCA = 2.25 V in some way. Could this be the solution?

 

The other problem is to know what is the output current of the ADG3308 in digital I/O, this data is not given in the datashhet and it is very important to know it since in the ADG3308 it says:

 

INPUT DRIVING REQUIREMENTS To ensure correct operation of the ADG3308/ADG3308-1, the circuit that drives the input of the device should be able to ensure rise/fall times of less than 3 ns when driving a load consisting of a 6 kΩ resistor in parallel with the input capacitance of the ADG3308/ADG3308-1 channel.

 

Then: 3ns --> 4.5pF --> V=2.5V 

IC(rise/fall)=(2.5V/3ns)x4.5pF = 3.75mA  plus 2.5/6k = 416uA   Total: 4.16mA  

Can the ADG3308 give this current and, if so, what is the final output voltage?

 

Thank a lot

JJclaver

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