ADAS3022 datasheet(28/40 Pages) AD

28 / 40 page

ADAS3022

Data Sheet

Rev. A | Page 28 of 40

VOLTAGE REFERENCE OUTPUT/INPUT

The ADAS3022 allows the choice of an internal reference or an

external reference using the on-chip buffer/amplifier, or an

external reference.

The internal reference of the ADAS3022 provides excellent

performance and can be used in almost all applications. To set

the reference selection mode, use the internal reference enable bit

(REFEN) and the REFIN pin as described in this section. REF1

and REF2 must be tied together externally.

Internal Reference

The precision internal reference is factory trimmed and is

suitable for most applications.

Setting the REFEN bit in the CFG register to 1 (default) enables

the internal reference and produces 4.096 V on the REF1 and

REF2 pins; this 4.096 V output serves as the main system

reference. The unbuffered 2.5 V (typical) band gap voltage is

output on the REFIN pin, which requires an external parallel

decoupling using 10 µF and 0.1 µF capacitors to reduce the

noise on the output. Because the current output of REFIN is

limited, it can be used as a source if followed by a suitable buffer,

such as the AD8031. Note that excessive loading of the REFIN

output will also lower the 4.096 V system reference because the

internal amplifier uses a fixed gain.

The internal reference output is trimmed to the targeted value

of 4.096 V with an initial accuracy of ±8 mV. The reference is

also temperature compensated to provide a typical drift of

±5 ppm/°C.

When the internal reference is used, the ADAS3022 should be

decoupled as shown in Figure 62. Note that both REF1 and

REF2 connections are required, along with suitable decoupling

on the REFIN output and the RCAP internally regulated supply.

REF2

REF1

RCA

REFN

RGND

BAND

GAP

ADAS3022

0.1

µF

REFIN

REFN

µF

0.1

µF

0.1

µF

REFN

Figure 62. 4.096 V Internal Reference Connection

External Reference and Internal Buffer

The external reference and internal buffer are useful when a com-

mon system reference is used or if improved drift performance

is required.

Setting REFEN to 0 disables the internal band gap reference,

allowing the user to provide an external voltage reference (2.5 V

typical) to the REFIN pin. The internal buffer remains enabled,

thus reducing the need for an external buffer amplifier to generate

the main system reference. With REFIN = 2.5 V, REF1 and REF2

output 4.096 V, which serves as the main system reference.

For this configuration, connect the external source as shown

in Figure 63. Any type of 2.5 V reference, including those with

low power, low drift, and a small package, can be used in this

configuration because the internal buffer handles the dynamics

of the ADAS3022 reference.

REF2

REF1

RCAP

REFN

RGND

BAND

GAP

ADAS3022

0.1

µF

REFIN

REFN

µF

0.1

µF

0.1

µF

REFN

REFERENCE

SOURCE = 2.5V

Figure 63. External Reference Using Internal Buffer

External Reference

For applications that require a precise, low drift 4.096 V reference,

an external reference can also be used.

This option requires disabling the internal buffer by setting

REFEN to 0 and driving or connecting REFIN to AGND; therefore,

both hardware and software control are necessary. Attempting

to drive the REF1 and REF2 pins prior to disabling the internal

buffer can cause source/sink contention in the driving amplifiers.

Connect the precision 4.096 V reference, which serves as the

main system reference, through a low impedance buffer (such as

the AD8031 or the AD8605) to REF1 and REF2 as shown in

Figure 64. Recommended references include the ADR434,

ADR444, and ADR4540.

REF2

REF1

RCAP

REFN

RGND

BAND

GAP

ADAS3022

0.1

µF

REFIN

REFN

µF

0.1

µF

1µF

REFERENCE

SOURCE = 4.096V

Figure 64. External Reference

If an op amp is used as the external reference source, take note

of any concerns regarding driving capacitive loads. Capacitive

loading for op amps usually refers to the ability of the amplifier

to remain marginally stable in ac applications but can also play

a role in dc applications, such as a reference source. Keep in

mind that the reference source sees the dynamics of the bit

decision process on the reference pins and further analysis

beyond the scope of this data sheet may be required.

ADAS3022 数据表(PDF) 28 Page - Analog Devices

ADAS3022 数据表(HTML) 28 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

数据表下载

链接网址

ADAS3022 数据表(PDF) 28 Page - Analog Devices

ADAS3022 数据表(HTML) 28 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

数据表 下载

链接网址

数据表下载