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AD7626 Ref input current value

Question asked by shackleton on Nov 19, 2014
Latest reply on Nov 20, 2014 by shackleton

Hi to all,

 

my acquisition and processing board has 12 AD7626 channels interfaced with a FPGA.

I have to provide a voltage reference source for all ADCs in simultaneous acquisition mode at 10MSPS.

 

So, following the application note "Voltage Reference Design for Precision Successive-Approximation ADCs" by Alan Walsh,

I choose the topology using a unit gain op-amp amplifier for each ADC (each op-amp fed from a unique ADR4540 voltage reference): see the topology below suggested in the AD7626 datasheet.

AD7626_external_Voltage_Reference_topology.bmp

Supposing a AD7626 Vref input current value of 3.3mA average (10 times the AD7980; 1MSPS Pulsar ADC), I should

select a op-amp with internal output impedance low as 0.01 Ohm at 10MHz: this value is too low even for hi-speed op-amp like ADA4841.

 

So my question is regarding the AD7626 Ref input current value: is my hypothesis correct (Iref = 10 * Irref_AD7980)?

May be the AD7626 has a different internal topology and, for this reason, the Iref value is negligible and is not provided?

 

Thank you for any help.

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