ADA4941-1YRZ-R7 datasheet(20/23 Pages) AD

20 / 23 page

ADA4941-1

Data Sheet

Rev. D | Page 20 of 23

APPLICATIONSINFORMATION

OVERVIEW

The ADA4941-1 is an adjustable-gain, single-ended-to-differential

voltage amplifier, optimized for driving high resolution ADCs.

Single-ended-to-differential gain is controlled by one feedback

network, comprised of two external resistors: RF and RG.

USING THE REF PIN

The REF pin sets the output baseline in the inverting path and

is used as a referencefor the input signal. In most applications,

the REF pin is set to the input signal midswing level, which in

many cases is also midsupply.Forbipolarsignalsanddual power

supplies, REF is generally set to ground. In single-supply

applications, setting REF to the input signal midswing level

provides optimal output dynamicrange performance with

minimum differential offset. Notethat the REF input only

affects the inverting signal path or VON.

Most applications require a differential output signal with the

same dccommon-mode level on each output. It is possible for

the signal measured across VOP and VON to have a common-

mode voltage thatis of the desired level but not common to

both outputs. This type of signal is generally avoided because

it does not allow for optimal use ofthe output dynamicrange of

the amplifier.

Defining VIN as the voltage appliedto the input pin, the

equations that govern thetwo signal paths aregiven in

Equation 21 and Equation 22.

VOP = VIN

(21)

VON = −VIN + 2 (REF)

(22)

When the REF voltage is set to the midswing level of the input

signal, the two output signals fall directly on top of each other

with minimal offset. Setting the REF voltage elsewhereresults

in an offset between the two outputs.

The best use of the REF pin can be further illustratedby

considering a single-supply case with a 10 V power supply and

an input signal that varies between 2 V and 7 V. This is a case

where the midswing level of the input signal is not at midsupply

but is at 4.5 V. Setting the REF input at 4.5 V and neglecting

offsets, Equation 21 and Equation 22 are usedto calculate the

results. When the input signal is at its midpoint of 4.5 V, OUT+

is at 4.5 V, as is VON. This can be considered as a baseline state

wherethedifferentialoutput voltageis 0. When theinput increases

to 7 V, VOP tracks the input to 7 V, and VON decreases to 2 V.

This can be viewed as a positivepeaksignal wherethedifferential

output voltageequals 5 V. When the input signal decreasesto

2 V, VOP again tracks to 2 V, and VON increases to 7 V. This

can be viewed as a negative peaksignal where thedifferential

output voltageequals −5 V. The resulting differential output

voltage is 10 V p-p.

The previous discussion revealshow the single-ended-to-

differential gain of 2 is achieved.

INTERNAL FEEDBACK NETWORK POWER

DISSIPATION

While traditional op amps do not haveon-chipfeedback

elements, the ADA4941-1 contains two on-chip, 1 kΩ resistors

that comprise an internal feedbackloop. The powerdissipated

in these resistorsmustbeincluded in theoverall power dissipation

calculations for the device. Under certain circumstances, the

power dissipated in these resistors could be comparable to the

quiescentdissipationofthedevice. Forexample, on ±5V supplies

with the REF pin tied to ground and OUT− at +4 VDC, each

1 kΩ resistor carries 4 mA and dissipates 16 mW for a total of

32 mW. This is comparable to the quiescent powerand must

therefore be included in the overall device powerdissipation

calculations. For acsignals, rms analysis is required.

DISABLE FEATURE

The ADA4941-1 includes a disable featurethat can be asserted

to minimize power consumption in a device that is not needed

at a particular time. When asserted, the disable feature does not

place the device outputin a high impedanceortristatecondition.

The disable feature is active high. See the Specifications tables

for the high and low level voltage specifications.

ADA4941-1YRZ-R7 データシート(PDF) 20 Page - Analog Devices

ADA4941-1YRZ-R7 データシート(HTML) 20 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

データシートダウンロード