AD8475 datasheet(30/42 Pages) AD

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LTC6363 Family

Rev. C

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V+

CDIFF

3.3nF

CCM

3.3nF

CCM

3.3nF

AIN+

VREF

VDD

LTC2378-20

SAR ADC

2.5V

GND

AIN–

20-BIT

1Msps

6363 F05

RFILT

30.1

RFILT

30.1

VOCM

–OUT

0.1µF

VIN

V–

V+

V–

1050

3.6M

–

LTC6363-1

+OUT

V+

–IN

+IN

1050

3.6M

0.1µF

2.5V

VOCM

0.1µF

–1V

V–

SHDN

Figure 5. Recommended Interface Solution for Driving the LTC2378-20 SAR ADC

settling. For lowest distortion, choose capacitors with low

dielectric absorption (such as a C0G multilayer ceramic

capacitor). In general, large capacitor values attenuate

the fixed nonlinear charge kickback; however very large

capacitor values will detrimentally load the driver at the

desiredinputfrequencyandcausedriverdistortion.Smaller

input swings will allow for larger filter capacitor values

due to decreased loading demands on the driver. This

property may be limited by the particular input amplitude

dependence of differential nonlinear charge kickback for

the specific ADC.

In some applications, placing series resistors at the inputs

of the ADC may further improve distortion performance.

These series resistors function with the ADC sampling

capacitor to filter potential ground bounce or other high

speed sampling disturbances. Additionally, the resistors

limit the rise time of residual filter glitches that manage to

propagate to the driver outputs. Restricting possible glitch

propagation rise time to within the small signal bandwidth

of the driver enables less disturbed output settling.

For the specific application of LTC6363 driving the

LTC2378-20 SAR ADC, the recommended component

values of the RC filter are provided in Figure 5. These

component values are chosen for optimal distortion and

noise performance.

APPLICATIONS INFORMATION

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