AD7677AST datasheet(13/21 Pages) AD

13 / 21 page

REV. A

AD7677

–12–

The Warp Mode allows the fastest conversion rate up to 1 MSPS.

However, in this mode, and this mode only, the full specified accu-

racy is guaranteed only when the time between conversion does

not exceed 1 ms. If the time between two consecutive conversions

is longer than 1 ms, for instance, after power-up, the first conver-

sion result should be ignored. This mode makes the AD7677

ideal for applications where fast sample rates are required.

The Normal Mode is the fastest mode (800 kSPS) without any

limitation about the time between conversions. This mode makes

the AD7677 ideal for asynchronous applications such as data

acquisition systems, where both high accuracy and fast sample

rate are required.

The Impulse Mode, the lowest power dissipation mode, allows

power saving between conversions. The maximum throughput

in this mode is 666 kSPS. When operating at 100 SPS, for

example, it typically consumes only 15

µW. This feature makes

the AD7677 ideal for battery-powered applications.

Transfer Functions

Using the OB/

2C digital input, the AD7677 offers two output

codings: straight binary and two’s complement. The ideal trans-

fer characteristic for the AD7677 is shown in Figure 4.

000...000

000...001

000...010

111...101

111...110

111...111

ANALOG INPUT

+FS – 1.5 LSB

+FS – 1 LSB

–FS + 1 LSB

–FS

–FS + 0.5 LSB

Figure 4. ADC Ideal Transfer Function

TYPICAL CONNECTION DIAGRAM

Figure 5 shows a typical connection diagram for the AD7677.

Different circuitry shown on this diagram is optional and is

discussed below.

Analog Inputs

Figure 6 shows a simplified analog input section of AD7677.

AVDD

AGND

DGND

DVDD

OVDD

OGND

SER/

PAR

CNVST

BUSY

SDOUT

SCLK

RESET

REFGND

CREF

2.5V REF

NOTE 1

REF

100

CLOCK

AD7677

C/ P/DSP

SERIAL PORT

DIGITAL SUPPLY

(3.3V OR 5V)

ANALOG

SUPPLY

(5V)

DVDD

OB/

NOTE 7

BYTESWAP

DVDD

50k

100nF

IN+

ANALOG INPUT+

2.7nF

NOTE 4

NOTE 5

AD8021

–

NOTE 2

NOTE 3

NOTE 6

ADR421

10 F

100nF

10 F

100nF

10 F

IN–

ANALOG INPUT–

2.7nF

NOTE 4

NOTE 5

AD8021

–

1 F

NOTES

1. SEE VOLTAGE REFERENCE INPUT SECTION.

2. WITH THE RECOMMENDED VOLTAGE REFERENCES, CREF IS 47 F. SEE CHAPTER VOLTAGE REFERENCE INPUT SECTION.

3. OPTIONAL CIRCUITRY FOR HARDWARE GAIN CALIBRATION.

4.THE AD8021 IS RECOMMENDED. SEE DRIVER AMPLIFIER CHOICE SECTION.

5. SEE ANALOG INPUT SECTION.

6. OPTION, SEE POWER SUPPLY SECTION.

7. OPTIONAL LOW JITTER

CNVST, SEE CONVERSION CONTROL SECTION.

Figure 5. Typical Connection Diagram

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