Rainbow-electronics ADC12062 Manual do Utilizador descarregar pdf (Página 13)

Applications Information (Continued)

TL/H/11490– 18

FIGURE 8. Buffering the Input with an LM6361 High Speed Op Amp

Another benefit of using a high speed buffer is improved

THD performance when using the multiplexer of the

ADC12062. The MUX on-resistance is somewhat non-linear

over input voltage, causing the RC time constant formed by

MUX

, and R

to vary depending on the input voltage.

This results in increasing THD with increasing frequency.

Inserting the buffer between the MUX OUT and the ADC IN

terminals as shown in

Figure 8

will eliminate the loading on

MUX

, significantly reducing the THD of the multiplexed sys-

tem.

Correct converter operation will be obtained for input volt-

ages greater than AGND

50 mV and less than AV

50 mV. Avoid driving the signal source more than 300 mV

higher than AV

, or more than 300 mV below AGND. If an

analog input pin is forced beyond these voltages, the cur-

rent flowing through that pin should be limited to 25 mA or

less to avoid permanent damage to the IC. The sum of all

the overdrive currents into all pins must be less than 50 mA.

When the input signal is expected to extend more than

300 mV beyond the power supply limits for any reason (un-

known/uncontrollable input voltage range, power-on tran-

sients, fault conditions, etc.) some form of input protection,

such as that shown in

Figure 9,

should be used.

TL/H/11490– 19

FIGURE 9. Input Protection

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