ADS5400IPZP datasheet(39/55 Pages) TI1

39 / 55 page

VIN (50

)

ADS5400

53 pF

26 pF

26 nH

VCM = 2.5 V

VCM

0.01 µF

Amplifier Supply Voltage:

Vs+ = 5 V

Vs± = 0 V

2.5 V

200

12.5

200

LMH4301

ADS5400

www.ti.com

SLAS611C – OCTOBER 2009 – REVISED JANUARY 2016

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

In the design of any application involving a high-speed data converter, particular attention should be paid to the

design of the analog input, the clocking solution, and careful layout of the clock and analog signals. The

ADS5400 evaluation module (EVM) is one practical example of the design of the analog input circuit and clocking

solution, as well as a practical example of good circuit board layout practices around the ADC.

8.2 Typical Application

The analog inputs of the ADS5400 must be fully differential and biased to an appropriate common mode voltage,

VCM. It is rare that the end equipment will have a signal that already meets the requisite amplitude and common

mode and is fully differential. Therefore, there will be a signal conditioning circuit for the analog input. If the

amplitude of the input circuit is such that no gain is needed to make full use of the full-scale range of the ADC,

then a transformer coupled circuit as used on the EVM may be used with good results. The transformer coupling

is inherently low-noise, and inherently AC-coupled so that the signal may be biased to VCM after the transformer

coupling.

If signal gain is required, or the input bandwidth is to include the spectrum all the way down to DC such that AC

coupling is not possible, then an amplifier-based signal conditioning circuit would be required. Figure 37 shows

LMH3401 interfaced with ADS5400. LMH3401 is configured to have to Single-Ended input with a differential

outputs follow by 1st Nyquist based low pass filter with 400 MHz bandwidth. Figure 37 also shows the power

supply recommendations for the amplifier.

Figure 37. ADS5400 Input Circuit Using an LMH3401 Fully Differential Amplifier

Clocking a High Speed ADC such as the ADS5400 requires a fully differential clock signal from a clean, low-jitter

clock source and driven by an appropriate clock buffer, often with LVPECL or LVDS signaling levels. The sample

clock must be biased up to the appropriate common-mode voltage, and the ADS5400 will internally bias the clock

to the appropriate common-mode voltage if the clock signal is AC-coupled as shown in Figure 38.

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