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ad5700 analog input

Question asked by Lijo on Apr 21, 2015
Latest reply on Apr 27, 2015 by tjohnson

Dear Sir,


we are testing hart protocol communication analog input.Here now we are not testing ADC portion...i am transmitting hart signal  using this circuit..i get hart signal at the HART_OUT pin of ad5700.but cant get the hart signal at 22 ohm side(transmitter connection side).

i tested

i am not used switch fully closed path instead.

for testing firstly i am not used hart transmitter(ABB temperature  hart transmitter)...then removed 250 ohm , 6.8 nf capacitor and TVS diode ,now i get hart signal at 22 ohm  side ,that is both side.....hart signal amplitude 600mV.Then i connect diode without  250 ohm resistor ,6.8 nf capacitor and then amplitude reduced to 400mV at 22 ohm side(left side of 2.2 uf)

when i am  connecting 6.8 nf without  250 ohm resistor that hart signal with amplitude 150 mV not coming at 22 ohm side (left side of 2.2 uf) when i connecting 250 ohm resistor  hart signal not comes.But at HART_OUT pin of ad5700 hart signal comes that is all voltage drops accross 2.2 uf.

any cases if i connect 250 ohm resistor hart signal not coming that i dont know........

there for testing i am not used 250 ohm then i connect transmitter (in transmitter +pin we connect positive pin of 24v and the next pin i connected same as the circuit but when i connecting transmitter then also hart signal is not comes....if connect 250 ohm resistor the same result also......

we connected hart  communicator  in place of transmitter i get receiving packet using hart modem..that means receiving side is ok....

we cant give hart signal to transmitter .......but the hart signal is coming at HART_OUT that signal not reaching at transmitter side..

i checked by removing receving side again but also the same result........

please help me why hart signal not reaching at transmitter side  when connecting transmitter or when connecting 250 ohm resistor..

please tell me its urgent thank you