ADC10D040

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SNAS149G – OCT 2001 – REVISED MARCH 2013

DYNAMIC PERFORMANCE

The ADC10D040 is a.c. tested and its dynamic performance is specified. To meet the published specifications,

the clock source driving the CLK input must be free of jitter. For best dynamic performance, isolating the ADC

clock from any digital circuitry should be done with adequate buffers, as with a clock tree. See Figure 39.

Figure 39. Isolating the ADC Clock from Digital Circuitry

COMMON APPLICATION PITFALLS

Driving the inputs (analog or digital) beyond the power supply rails. For proper operation, no input should

go more than 300 mV beyond the supply pins, Exceeding these limits on even a transient basis can cause faulty

or erratic operation. It is not uncommon for high speed digital circuits (e.g., 74F and 74AC devices) to exhibit

overshoot and undershoot that goes a few hundred millivolts beyond the supply rails. A resistor of 50

Ω to 100Ω

in series with the offending digital input, close to the source, will usually eliminate the problem.

Care should be taken not to overdrive the inputs of the ADC10D040 (or any device) with a device that is

powered from supplies outside the range of the ADC10D040 supply. Such practice may lead to conversion

inaccuracies and even to device damage.

Attempting to drive a high capacitance digital data bus. The more capacitance the output drivers have to

large charging current spikes can couple into the analog section, degrading dynamic performance. Adequate

bypassing and attention to board layout will reduce this problem. Buffering the digital data outputs (with a

74ACTQ841, for example) may be necessary if the data bus to be driven is heavily loaded. Dynamic

performance can also be improved by adding series resistors of 47

Ω to 56Ω at each digital output, close to the

ADC output pins.

Using a clock source with excessive jitter. This will cause the sampling interval to vary, causing excessive

output noise and a reduction in SNR and SINAD performance. The use of simple gates with RC timing as a clock

source is generally inadequate.

Copyright © 2001–2013, Texas Instruments Incorporated

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