AD4682 datasheet(16/30 Pages) AD

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AD4682/AD4683

Data Sheet

Rev. 0 | Page 16 of 30

APPLICATIONS INFORMATION

Figure 35 shows an example of the typical connection diagram

for the AD4682 and the AD4683. Decouple the VCC, VLOGIC,

REGCAP, and REFIO pins with suitable decoupling capacitors

as shown in Figure 35.

The exposed pad is a ground reference point for circuitry on

the devices and must be connected to the PCB ground.

Place a differential RC filter on the analog inputs to ensure

optimal performance is achieved.

The performance of the AD4682 and the AD4683 devices can be

impacted by noise on the digital interface. This impact is

dependent on the on-board layout and design. Keep a minimal

distance between the digital line to the digital interface, or place

a 100 Ω resistor in series and close to the SDOA pin and the

SDOB/ALERT pin to reduce noise from the digital interface

coupling of the AD4682 and the AD4683.

The two pseudo differential ADC channels of the AD4682 and

the AD4683 can accept an input voltage range from 0 V to VREF

on AINA+ and AINB+, and a VREF/2 voltage on AINA− and AINB−.

The AINA+, AINB+, AINA−, and AINB− analog input pins can be

driven with an amplifier. Table 9 lists the recommended driver

amplifiers that best fit and add value to the application. The

AD4682 and the AD4683 have a buffered internal 2.5 V reference

that is accessed via the REFIO pin. The buffered internal 2.5 V

reference must use an external buffer, like the ADA4807-2,

when connecting the reference to the external circuitry. The

AD4682 and the AD4683 have an option to use an ultralow

noise, high accuracy voltage reference as an external voltage

source ranging from 2.5 V to 3.3 V, such as the ADR4533 and

ADR4525.

POWER SUPPLY

The typical application circuit in Figure 35 can be powered by

a single 5 V voltage source (V+) that supplies the entire signal

chain. The 5 V supply can come from a low noise, CMOS low

dropout (LDO) regulator (ADP7105). The driver amplifier supply

is supplied by the +5 V (V+) and −2.5 V negative supply rail (V−),

which is derived from the inverter (ADM660). The inverter

converts the +5 V to −5 V and supplies the voltage to the

ADP7182 low noise voltage regulator to output the −2.5 V. The

two independent supplies of the AD4682 and the AD4683, VCC

and VLOGIC, that supply the analog circuitry and digital interface,

respectively, can be supplied by a low quiescent current LDO

regulator, such as the ADP166. The ADP166 is a suitable supply

with a fixed output voltage range from 1.2 V to 3.3 V for typical

VCC and VLOGIC levels. Decouple both the VCC supply and the

VLOGIC supply separately with a 1 µF capacitor. Additionally, an

internal LDO regulator supplies the AD4682 and the AD4683. The

on-chip regulator provides a 1.9 V supply for internal use on the

device only. Decouple the REGCAP pin with a 1 µF capacitor

connected to GND.

Power-Up

The AD4682 and the AD4683 are not easily damaged by power

supply sequencing. VCC and VLOGIC can be applied in any

sequence. Apply an external reference after VCC and VLOGIC are

applied.

The AD4682 and the AD4683 require a tPOWERUP time from

applying VCC and VLOGIC until the ADC conversion results are

stable. Applying CS pulses or interfacing with the AD4682 and

the AD4683 prior to the setup time elapsing does not have a

negative impact on ADC operation. Conversion results are not

guaranteed to meet data sheet specifications during this time,

however, and must be ignored.

Table 9. Signal Chain Components

Companion Parts

Part Name

Description

Typical Application

ADC Driver

ADA4896-2

1 nV/√Hz, rail-to-rail output amplifier

Precision, low noise, high frequency

ADA4940-2

Ultra low power, full differential, low distortion

Precision, low density, low power

ADA4807-2

1 mA, rail-to-rail output amplifier

Precision, low power, high frequency

LTC6227

1 nV/√Hz, 420 MHz gain bandwidth product (GBW), rail-

to-rail output amplifier

Precision, low noise, high frequency

External Reference

ADR4525

Ultralow noise, high accuracy 2.5 V voltage reference

2.5 V reference voltage

ADR4533

Ultralow noise, high accuracy 3.3 V voltage reference

3.3 V reference voltage

LDO

ADP166

Very low quiescent, 150 mA, LDO regulator

3.0 V to 3.6 V supply for VCC and VLOGIC

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