AD7888_EvalBoard| Application Note

AD7888_EvalBoard| Application Note

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FEATURES

Evaluation Board for 2.7V to 5.25V, Micro Power, 8-Channel, 125 kSPS, 12-Bit ADC EVAL-AD7888CB
Interfacing to this board is through a 96-way connector. This 96-way connector is compatible with the EVAL-CONTROL BOARD which is also available from Analog Devices. External sockets are provided for the AIN1-AIN8 inputs.
OPERATING THE AD7888 EVALUATION BOARD Power Supplies

Full-Featured Evaluation Board for the AD7888 EVAL-CONTROL BOARD Compatible Stand Alone Capability On-Board Analog Buffering and Reference Various Linking Options PC Software for Control and Data Analysis when used with EVAL-CONTROL BOARD

When using this evaluation board with the EVAL-CONTROL BOARD all supplies are provided from the EVALCONTROL BOARD through the 96 way connector. When using the board as a stand alone unit external supplies must be provided. This evaluation board has seven power supply inputs: VDD, AGND, +12V, -12V, AGND, DVDD and DGND. +5V/+3V must be connected to the VDD input to supply the AD7888 VDD pin. +12V and -12V are used to supply the OP467 quad op-amps and the AD780 voltage reference. 0V is connected to one or both of the AGND inputs. The DVDD input can be used to supply a separate +5V for the 74LS04 and the DGND input must be tied to 0V. Alternatively the 74LS04 can be supplied from the same +5V as the AD7888 supply by inserting LK15 . The supplies are decoupled to the relevant ground plane with 10uF tantalum and 0.1uF multilayer ceramic capacitors at the point where they enter the board. The supply pins of the AD7888, quad op-amps and reference are also decoupled to AGND with 10uF tantalum and a 0.1uF ceramic capa
citor. Extensive ground planes are used on this board to minimize the effect of high frequency noise interference. There are two ground planes, AGND and DGND. These are connected at one location close to the AD7888.

INTRODUCTION

This Technical Note describes the evaluation board for the AD7888, high speed, low power, 12-bit ADC that operates from a single 2.7 V to 5.25 V power supply. The AD7888 is capable of a 125 ksps throughput rate. The input track-andhold acquires a signal in 500 ns and features a single ended sampling scheme. The AD7888 contains eight single-ended analog inputs, AIN1 through AIN8. The analog input on each of these channels is from 0 to VREF. The part is capable of converting full power signals up to 2.5MHz. Full data on the AD7888 is available in the AD7888 data sheet available from Analog Devices and should be consulted in conjunction with this Technical Note when using the Evaluation Board. On-board components include an AD780 which is a pin programmable +2.5V or +3V ultra high precision bandgap reference, three OP467 quad op-amps and a 74LS04 inverting buffer. There are various link options which are explained in detail on page 2.

FUNCTIONAL BLOCK DIAGRAM
Ain1 R C F ilte r A in 1 CS SC LK DO UT Ain8 R C F ilte r A in 8 D IN

V o lta g e R e f e re n c e

R e f in / o u t

E x te r n a l R e f e re n c e

A D 7888 A D C
B i-p o la r In p u t B ia s- u p C irc u it U n i-p o la r O u tp u t P o w e r S u p p ly C irc u it

REV. A
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