ANALOG DEVICES AD7985 Service Manual

16-Bit, 2.5 MSPS, PulSAR

AD7985

0V

TO

V

REF

NOTES

1. GND REFE RS 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-WI RE
INTERFACE:
SPI, CS,
DAISY CHAIN
(TURBO = LOW)

TURBO

10µF

IN+

IN–

07947-001

15.5 mW ADC in LFCSP

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

0 V to V

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

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

Type 100 kSPS 250 kSPS 400 kSPS to 500 kSPS ≥1000 kSPS ADC Driver

14-Bit AD7940 AD79422 AD79462
16-Bit AD7680 AD7685
AD7683 AD76872 AD76882 AD79832 ADA4841-x
AD7684 AD7694 AD76932 AD79853 AD8021
18-Bit AD76912 AD76902 AD79822 ADA4941-1
AD79842 ADA4841-x
AD79863 AD8021

1

See www.analog.com for the latest selection of PulSAR ADCs and ADC drivers.

2

Pin-for-pin compatible with all other parts marked with this endnote.

3

The AD7985 and AD7986 are pin-for-pin compatible.

Rev. A

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with V

REF

REF

up to 5.0 V

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 CN V, th e
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 inter­face 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.

1

2

AD7686

2

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]
Fax: [phone] ©2009-2010 Analog Devices, Inc. All rights reserved.

APPLICATION DIAGRAM

Figure 1.

AD79802 ADA4941-1

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