ADAU1977WBCPZ-R7 datasheet(23/68 Pages) AD

23 / 68 page

Data Sheet

ADAU1977

Rev. C | Page 23 of 68

DIAGNOSTICS

The diagnostics block monitors the input pins in real time and

reports a fault as an interrupt signal on the FAULT pin (Pin 8),

which triggers sending an interrupt request to an external

controller. The diagnostics status registers (Register 0x11 through

Refer to the register map table (Table 25) and the register details

tables (Table 42, Table 43, Table 44, and Table 45) for more infor-

mation about the diagnostics register content. The diagnostics

can be enabled or disabled for each channel using Bits[3:0] of

is enabled and the microphone is connected as recommended

in the appropriate application circuit (see Figure 21).

Diagnostics Reporting

The diagnostics status is reported individually for each channel

in Register 0x11 through Register 0x14. The faults listed in

Table 13 are reported on each input pin.

Table 13. Faults Reported

Fault

AINxP

AINxN

Short to Battery

Yes

Short to MICBIAS

Yes

Short to Ground

Yes

Short Between Positive and Negative Inputs

Yes

Open Input

Yes

Diagnostics Adjustments

Short Circuit to Battery Supply

When an input terminal is shorted to the battery, the voltage at

the terminal approaches the battery voltage. Any voltage higher

than the set threshold is reported as a fault. The threshold can

be set using the SHT_B_TRIP bits, Bits[1:0] of Register 0x17

(see Table 14).

Table 14. Setting the Short to Battery Threshold

SHT_B_TRIP

(Register 0x17, Bits[1:0])

Short to Battery Threshold

0.95 × VBAT

0.9 × VBAT

0.85 × VBAT

0.975 × VBAT

Short Circuit to MICBIAS

This feature is supported only on the AINxP terminal. When

an AINxP terminal is shorted to MICBIAS, the voltage at the

AINxP terminal approaches the MICBIAS voltage. Any voltage

higher than the set threshold is reported as a fault. The threshold

can be set using the SHT_M_TRIP bits, Bits[5:4] of Register 0x17

(see Table 15).

Table 15. Setting the Short to MICBIAS Threshold

SHT_M_TRIP

(Register 0x17, Bits[5:4])

Short to MICBIAS Threshold

0.95 × MICBIAS

0.9 × MICBIAS

0.85 × MICBIAS

0.975 × MICBIAS

Short Circuit to Ground

When an input terminal is shorted to ground, the terminal

voltage reaches close to 0 V. Any voltage lower than the set

threshold is reported as a fault. The threshold is referenced to

VREF and, therefore, scales with the voltage at the VREF pin.

The threshold can be set using the SHT_G_TRIP bits, Bits[3:2]

of Register 0x17 (see Table 16).

Table 16.

SHT_G_TRIP

(Register 0x17, Bits[3:2])

Short to Ground Threshold

0.2 × VREF

0.133 × VREF

0.1 × VREF

0.266 × VREF

Microphone Terminal Short Circuited

When both input terminals are shorted, both the AINxP and

AINxN input terminals are at the same voltage—around

MICBIAS/2. Any voltage between the set thresholds is reported

as a fault. The upper and lower threshold voltages can be set

using the SHT_T_TRIP bits, Bits[7:6] of Register 0x17 (see

Table 17).

The following equations can be used to calculate the upper and

lower thresholds:

Upper Threshold = MICBIAS(0.5 + x)

Lower Threshold = MICBIAS(0.5 − x)

where x can be set using the SHT_T_TRIP bits, Bits[7:6] of

Table 17.

SHT_T_TRIP

(Register 0x17, Bits [7:6])

0.035

0.017

0.071

Reserved

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