MAX11040 datasheet(13/31 Pages) MAXIM

13 / 31 page

24-Bit, 4-Channel, Simultaneous-Sampling,

Cascadable, Sigma-Delta ADC

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When the analog input voltage changes between the

ADC full scale and the fault threshold faster than the

latency of the converter, OVRFLW goes low with the

FAULT output. OVRFLW remains invalid until a valid

clock frequency is available at XIN.

Overvoltage Fault Detection and Recovery (

FAULT)

With overvoltage fault protection enabled (FAULTDIS =

0), FAULT immediately transitions from a high to low

when any of the analog inputs go outside the voltage

range bounded by the fault-detection thresholds VPFT

and VNFT.

Once the analog inputs return back within the fault

thresholds, the FAULT interrupt output goes high after a

delay called the fault-recovery time. The fault-recovery

time is:

20 x tDOUT < fault-recovery time < 25 x tDOUT

where tDOUT is the data output period determined by

fXINCLOCK and the selected output data rate.

In the event the analog input voltage changes between

the ADC full scale and the fault threshold faster than

the latency of the converter, the ADC conversion result

prematurely jumps to the full-scale value when a fault is

detected (see Detection Discontinuity in Figure 4).

During a fault condition and the subsequent fault-

recovery time, the ADC conversion result remains at full

scale. This creates a discontinuity in the digital conver-

sion result only if the fault recovery time is greater than

the latency plus the time that the input changes

between the fault threshold and the ADC full scale (see

Recovery Discontinuity in Figure 4). Neither of these

steps occur if the fault-protection circuitry is disabled

(FAULTDIS = 1), or if the input is slow relative to the

above descriptions (see Figure 5).

For data rates faster than 32ksps (FSAMPC = 111), the

converter output may contain invalid data for up to

188µs after FAULT returns high. To prevent this behav-

ior, disable the overvoltage fault protection by setting

the FAULTDIS bit in the configuration register to 1 when

using FSAMPC = 111, and limit the analog input swing

to ±3.5V.

|AIN+ - AIN-|

LATENCY

DETECTION

DISCONTINUITY

RECOVERY

DISCONTINUITY

FULL SCALE

(|0.88VREF|)

FAULT-DETECTION

THRESHOLD

(VPFT OR |VNFT|)

RECOVERY TIME

LATENCY

FAULT

OVRFLW

DIGITAL OUTPUT

DATA AT DOUT

Figure 4. High-Frequency Analog Input Overvoltage Detection and Recovery

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