24-Bit, DC to 50 kHz Input Bandwidth, Multichannel, Low Noise Precision Sigma-Delta ADC with PGA

The AD4170-4 is a DC to 50 kHz input bandwidth, low noise, high speed, completely integrated analog front end for high precision measurement applications. The AD4170-4 offers output data rates from 7.6 SPS up to 500 kSPS. The device contains a low noise, 24-bit Σ-Δ analog-to-digital converter (ADC), and can be configured to have four differential inputs or eight single-ended or pseudodifferential inputs. The on-chip low noise gain stage ensures that signals of small amplitude can be interfaced directly to the AD4170-4.

The AD4170-4 offers the highest degree of signal chain integration. The device contains an internal reference and accepts two external differential references, which can be internally buffered. Other key integrated features include the following:

* Programmable gain amplifier (PGA). Due to the programmable

gain (0.5 to 128), the PGA allows direct interfacing to transducers

with low output amplitudes such as resistive bridges, thermocouples,

and resistance temperature detectors (RTDs).

* The PGA has a wide common-mode input range, giving designers

greater margin for widely varying input common modes.

* Low drift, well matched precision current sources. Excitation

current sources can be used to excite 2-, 3-, and 4-wire RTDs

or bridge type sensors. Excitation current output options include

10 μA, 50 μA, 100 μA, 250 μA, 500 μA, 1 mA, and 1.5 mA. The

currents can also be added if higher currents are needed. The

currents are made up of two pairs with the pairs optimized for

matching and drift matching.

* The low-side power switch (PDSW) can be used to power down

bridge sensors between conversions.

* Voltage bias for thermocouples (the VBIAS source sets the

common-mode voltage of a channel to (AVDD + AVSS)/2.

* The smart sequencer allows the conversion of each enabled

preconfigured channel in a predetermined order, allowing a mix

of transducer, system checks, and diagnostic measurements to

be interleaved. The sequencer eliminates the need for repetitive

serial interface communication with the device to change configuration.

Sixteen channels can be configured in the sequence.

Each of these channels selects from eight user-defined ADC

setups that allow selection of gain, filter type, output data rate,

buffering, and reference source.

The AD4170-4 also has extensive diagnostic functionality integrated as part of its comprehensive feature set. These diagnostics include a cyclic redundancy check (CRC), signal chain checks, and serial interface checks, which lead to a more robust solution.

The device also offers a multitude of digital filter options, ensuring that the user has the highest degree of flexibility. The device contains a finite impulse response (FIR) filter which offers low pass-band ripple for analog inputs from DC up to 50 kHz, quick roll-off and excellent stop-band rejection. Also available in this device is a programmable FIR filter that can accept up to 72 user coefficients. The part contains sinc filters which allow faster settling in multiplexed applications. In addition, the AD4170-4 offers multiple options for simultaneous 50 Hz and 60 Hz rejection.

The AD4170-4 also has overvoltage/undervoltage tolerance. If a channel has a signal which is slightly beyond AVDD or AVSS, adjacent channels can continue to function and convert correctly. The embedded features, diagnostics, and intelligence minimize the component count when designing a signal chain, resulting in reduced board space needs, reduced design cycle times, and cost savings.

The device operates with a single analog power supply from 4.75 V to 5.25 V or a bipolar +2.5 V power supply. The digital supply has a range of 1.7 V to 5.25 V. The device is specified for a temperature range of −40°C to +105°C. The AD4170-4 is housed in a 32-lead LFCSP package.

APPLICATIONS

* Industrial process control: PLC/DCS modules

* Temperature and pressure measurement

* High accuracy medical and scientific instrumentation

* Chromatography

* Seismic and energy exploration

* Electrical test and measurement

* Acoustic analysis

* Instrumentation

* Weigh scale

* Precision AC and DC performance

* Noise RTI 5.5 nV/√Hz (gain = 128)

* INL: ±0.5 ppm of FSR

* SNR 110 dB typical (VREF = 4.096 V, gain = 1 precharge, sinc5 filter)

* THD: −120 dB typical

* Crosspoint multiplexed analog inputs

* 4 differential/8 pseudodifferential inputs

* Overvoltage/undervoltage tolerant on inactive analog inputs

* Channel scan data rate of 71.4 kSPS/channel (14 μs settling)

* Ultra-low noise integrated PGA, gains of 0.5 to 128

* Output data rate: 7.6 SPS to 500 kSPS

* Flexible digital filters

* Low ripple FIR: ±0.005 dB maximum pass-band ripple

* User programmable FIR filter options

* Low latency sinc filters

* Simultaneous 50 Hz/60 Hz rejection

* Band gap reference with 5 ppm/°C drift typical