CS5371 datasheet(15/22 Pages) CIRRUS

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CS5371 CS5372

DS255F3

9.3.

SCR Latch-up Considerations

The VA- pin is tied to the CS5371/72 substrate and

should always be connected to the most negative

supply voltage to ensure SCR latch-up does not

occur. In general, latch-up may occur when any

pin voltage (including the analog inputs) is 0.7V or

more below VA-, or 7.6V or more above VA-.

Analog inputs INR+/- and INF+/- should be voltage

limited to ensure signals don’t exceed the (VA-)-

0.7V or (VA+)+7.6V requirement. Either the inputs

should be clamped to the VA+ and VA- rails using

reversed biased Schottky diodes (BAT85 or simi-

lar), or the current into the analog inputs should be

limited to less than 10mA. By current limiting the

analog inputs, the internal ESD diodes on the ana-

log input pads will clamp the input signal to the

proper level. Input currents greater than 10mA will

overdrive the internal diodes, so external compo-

nents are required.

When using dual analog power supplies, it is rec-

ommended to connect the VA- power supply pin to

system ground (DGND) using a reversed biased

Schottky diode. This configuration clamps the VA-

voltage a maximum of 0.3V above ground to en-

sure SCR latch-up does not occur during power

up. If the VA+ power supply ramps before the VA-

supply, the VA- voltage could be pulled above

ground through the CS5371/72. If the VA- supply

is unintentionally pulled 0.7 V above the DGND

pin, SCR latch-up can occur.

9.4.

DC-DC Converter Considerations

Many measurement systems are battery powered

and utilize DC-DC converters to generate the nec-

essary supply voltages for the system. To mini-

mize the effects of interference, it is desirable to

operate the DC-DC converter at a frequency which

is rejected by the digital filter.

9.5.

Power Supply Rejection

Power supply rejection of the CS5371/72 modula-

tors is frequency dependent. The digital filter re-

jects power supply noise for frequencies above the

filter corner frequency at 130 dB or greater. For

frequencies between DC and the digital filter cor-

ner frequency, power supply rejection is nearly

constant at 90 dB.

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