1 Features

• 12-bit ADC with integrated analog front-end

• High speed:

– ADS8661: 1.25 MSPS

– ADS8665: 500 kSPS

• Software programmable input ranges:

– Bipolar ranges: ±12.288 V, ±10.24 V, ±6.144 V,

±5.12 V, and ±2.56 V

– Unipolar ranges: 0 V–12.288 V, 0 V–10.24 V,

0 V–6.144 V, and 0 V–5.12 V

• 5-V analog supply: 1.65-V to 5-V I/O supply

• Constant resistive input impedance ≥ 1 MΩ

• Input overvoltage protection: up to ±20 V

• On-chip, 4.096-V reference with low drift

• Excellent performance:

– DNL: ±0.1 LSB; INL: ±0.15 LSB

– SNR: 74 dB; THD: –102 dB

• ALARM → high, low threshold

• multiSPI™ interface with daisy-chain

• Extended industrial temperature range:

–40°C to +125°C

2 Applications

• Analog input modules

• Mixed modules (AI, AO, DI, DO)

• Data acquisition (DAQ)

• Trackside signaling and control

3 Description

The ADS8661 and ADS8665 belong to a family of

integrated data acquisition system based on a

successive approximation (SAR) analog-to-digital

converter (ADC). The devices feature a high-speed,

high-precision SAR ADC, integrated analog front-end

(AFE) input driver circuit, overvoltage protection circuit

up to ±20 V, and an on-chip 4.096-V reference with

extremely low temperature drift.

The devices operate on a single 5-V analog supply,

but support true bipolar input ranges of ±12.288 V,

±6.144 V, ±10.24 V, ±5.12 V, and ±2.56 V, as well as

unipolar input ranges of 0 V to 12.288 V, 0 V to

10.24 V, 0 V to 6.144 V, and 0 V to 5.12 V. The gain

and offset errors are accurately trimmed within the

specified values for each input range to ensure high

dc precision. The input range selection is done by

software programming of the device internal registers.

The devices offer a high resistive input impedance

(≥ 1 MΩ) irrespective of the selected input range.

The multiSPI digital interface is backward-compatible

to the traditional SPI protocol. Additionally,

configurable features simplify interface to a wide

range of host controllers.