ADA4932-1YCPZ-R7 datasheet(23/28 Pages) AD

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ADA4932-1/ADA4932-2

Rev. 0 | Page 23 of 28

4. The feedback resistor value is modified as a final gain

adjustment to obtain the desired output voltage.

To make the output voltage VOUT = 1 V p-p, calculate RF

using the following formula:

(

)(

) (

)(

)

Ω

−

Ω

−

509

524

Desired

OUT

The closest standard 1% value to 509 Ω is 511 Ω, which

gives a differential output voltage of 1.00 V p-p.

The final circuit is shown in Figure 63.

ADA4932-x

VOUT, dm

1.00V p-p

+VS

–VS

Ω

499

Ω

499

Ω

511

Ω

511

Ω

VOCM

2V p-p

1V p-p

53.6

Ω

RTS

25.5

Ω

Figure 63. Terminated Single-Ended-to-Differential System with G = 2

INPUT COMMON-MODE VOLTAGE RANGE

The ADA4932-x input common-mode range is shifted down

by approximately one VBE, in contrast to other ADC drivers

with centered input ranges such as the ADA4939-x. The

downward-shifted input common-mode range is especially

suited to dc-coupled, single-ended-to-differential, and single-

supply applications.

For ±5 V operation, the input common-mode range at the

summing nodes of the amplifier is specified as −4.8 V to +3.2 V,

and is specified as +0.2 V to +3.2 V with a +5 V supply. To

avoid nonlinearities, the voltage swing at the +IN and −IN

terminals must be confined to these ranges.

INPUT AND OUTPUT CAPACITIVE AC COUPLING

While the ADA4932-x is best suited to dc-coupled applications,

it is nonetheless possible to use it in ac-coupled circuits. Input

ac coupling capacitors can be inserted between the source and

RG. This ac coupling blocks the flow of the dc common-mode

feedback current and causes the ADA4932-x dc input common-

mode voltage to equal the dc output common-mode voltage.

These ac coupling capacitors must be placed in both loops to keep

the feedback factors matched. Output ac coupling capacitors can

be placed in series between each output and its respective load.

SETTING THE OUTPUT COMMON-MODE VOLTAGE

The VOCM pin of the ADA4932-x is internally biased with a vol-

tage divider comprised of two 50 kΩ resistors across the supplies,

with a tap at a voltage approximately equal to the midsupply

point, [(+VS) + (−VS)]/2. Because of this internal divider, the

VOCM pin sources and sinks current, depending on the externally

applied voltage and its associated source resistance. Relying on

the internal bias results in an output common-mode voltage

that is within about 100 mV of the expected value.

In cases where more accurate control of the output common-

mode level is required, it is recommended that an external

source or resistor divider be used with source resistance less

than 100 Ω. If an external voltage divider consisting of equal

resistor values is used to set VOCM to midsupply with greater

accuracy than produced internally, higher values can be used

because the external resistors are placed in parallel with the

internal resistors. The output common-mode offset listed in the

Specifications section assumes that the VOCM input is driven by a

low impedance voltage source.

It is also possible to connect the VOCM input to a common-mode

level (CML) output of an ADC; however, care must be taken to

ensure that the output has sufficient drive capability. The input

impedance of the VOCM pin is approximately 10 kΩ.If multiple

ADA4932-x devices share one ADC reference output, a buffer

may be necessary to drive the parallel inputs.

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