特徴

8 simultaneously sampled inputs

True bipolar analog input ranges: ±10 V, ±5 V

Single 5 V analog supply and 2.3 V to 5.25 V VDRIVE

Fully integrated data acquisition solution

Analog input clamp protection

Input buffer with 1 MΩ analog input impedance

Second-order antialiasing analog filter

On-chip accurate reference and reference buffer

18-bit ADC with 200 kSPS on all channels

Oversampling capability with digital filter

Flexible parallel/serial interface

SPI/QSPI™/MICROWIRE™/DSP compatible

Pin compatible solutions from 14-bits to 18-bits

パフォーマンス

7 kV ESD rating on analog input channels

98 dB SNR, −107 dB THD

Low power: 100 mW

Standby mode: 25 mW

 

アプリケーション

Power line monitoring and protection systems

Multiphase motor controls

Instrumentation and control systems

Multiaxis positioning systems

Data acquisition systems (DAS)

 

概要

The AD7608 is an 18-bit, 8-channel simultaneous sampling, analog-to-digital data acquisition system (DAS). The part contains analog input clamp protection, a second-order antialiasing filter,a track-and-hold amplifier, an 18-bit charge redistribution successive approximation analog-to-digital converter (ADC), a flexible digital filter, a 2.5 V reference and reference buffer, and high speed serial and parallel interfaces.The AD7608 operates from a single 5 V supply and can accommodate ±10 V and ±5 V true bipolar input signals while sampling at throughput rates up to 200 kSPS for all channels.The input clamp protection circuitry can tolerate voltages up to ±16.5 V. The AD7608 has 1 MΩ analog input impedance regardless of sampling frequency. The single supply operation, on-chip filtering, and high input impedance eliminate the need for driver op amps and external bipolar supplies. The AD7608 antialiasing filter has a 3 dB cutoff frequency of 22 kHz and provides 40 dB antialias rejection when sampling at 200 kSPS. The flexible digital filter is pin driven, yields improvements in SNR, and reduces the 3 dB bandwidth.

 

Analog Input Ranges

The AD7608 can handle true bipolar, single-ended input voltages. The logic level on the RANGE pin determines the analog input range of all analog input channels. If this pin is tied to a logic high, the analog input range is ±10 V for all channels. If this pin is tied to a logic low, the analog input range is ±5 V for allchannels. A logic change on the RANGE pin has an immediate effect on the analog input range; however, there is typically a settling time of approximately 80 µs, in addition to the normal acquisition time requirement. The recommended practice is to hardwire the RANGE pin according to the desired input range for the system signals. During normal operation, the applied analog input voltage should remain within the analog input range selected via the range pin. A RESET pulse must be applied after power-up to ensure the analog input channels are configured for the range selected. When in a power-down mode, it is recommended to tie the analog inputs to GND. As per the Analog Input Clamp Protection section, the overvoltage clamp protection is recommended for use in transient overvoltage conditions and should not remain active for extended periods. Stressing the analog inputs outside of the conditions mentioned here may degrade the Bipolar Zero Code error and THD performance of the AD7608.

 

Analog Input Impedance

The analog input impedance of the AD7608 is 1 MΩ. This is a fixed input impedance that does not vary with the AD7608sampling frequency. This high analog input impedance eliminates the need for a driver amplifier in front of the AD7608, allowing for direct connection to the source or sensor. With the need for a driver amplifier eliminated, bipolar supplies (which are often a source of noise in a system) can be removed from the signal chain.