16-Bit, 2.5 MSPS, PulSAR

15.5 mW ADC in LFCSP

AD7985

Rev. 0

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FEATURES

16-bit resolution with no missing codes

Throughput: 2.5 MSPS (TURBO high), 2.0 MSPS (TURBO low)

Low power dissipation

15.5 mW at 2.5 MSPS, with external reference

28 mW at 2.5 MSPS, with internal reference

INL: ±0.7 LSB typical, ±1.5 LSB maximum

SNR

88.5 dB, with on-chip reference

90 dB, with external reference

4.096 V internal reference: typical drift of ±10 ppm/°C

Pseudo differential analog input voltage range

Allows use of any input range

No pipeline delay

Logic interface: 1.8 V/2.5 V/2.7 V

Serial interface: SPI-/QSPI™-/MICROWIRE™-/DSP-compatible

Ability to daisy-chain multiple ADCs with busy indicator

20-lead, 4 mm × 4 mm LFCSP (QFN)

APPLICATIONS

Battery-powered equipment

Communications

ATE

Data acquisition systems

Medical instruments

APPLICATION DIAGRAM

0V

TO

NOTES

1. GND REFERS TO REFGND, AGND, AND DGND.

AD7985

GND REF

AVDD,

DVDD

VIO

BVDD

5V

2.5V

1.8V

TO

2.7V

VIO

SDI

SCK

SDO

CNV

3- OR 4-WIRE

INTERFACE:

SPI, CS,

DAISY CHAIN

(TURBO = LOW)

TURBO

10µF

IN+

IN–

Figure 1.

GENERAL DESCRIPTION

The AD7985 is a 16-bit, 2.5 MSPS successive approximation

analog-to-digital converter (SAR ADC). It contains a low power,

high speed, 16-bit sampling ADC, an internal conversion clock,

an internal reference (and buffer), error correction circuits, and

a versatile serial interface port. On the rising edge of CNV, the

AD7985 samples an analog input, IN+, between 0 V and REF

with respect to a ground sense, IN−. The AD7985 features a

very high sampling rate turbo mode (TURBO is high) and a

reduced power normal mode (TURBO is low) for low power

applications where the power is scaled with the throughput.

In normal mode (TURBO is low), the SPI-compatible serial inter-

face also features the ability, using the SDI input, to daisy-chain

several ADCs on a single 3-wire bus and provide an optional busy

indicator. It is compatible with 1.8 V, 2.5 V, and 2.7 V supplies

using the separate VIO supply.

The AD7985 is available in a 20-lead LFCSP with operation

specified from −40°C to +85°C.

Table 1. MSOP, LFCSP, 14-/16-/18-Bit PulSAR® ADCs1

Type

100 kSPS

250 kSPS

400 kSPS to 500 kSPS

≥1000 kSPS

ADC Driver

14-Bit

AD7940

AD79422

AD79462

16-Bit

AD7680

AD76852

AD76862

AD79802

ADA4941-1

AD7683

AD76872

AD76882

AD79832

ADA4841-x

AD7684

AD7694

AD76932

AD79853

AD8021

18-Bit

AD76912

AD76902

AD79822

ADA4941-1

AD79842

ADA4841-x

AD79863

AD8021