DOUT

CLKIN

127 CLKIN cycles

127 CLKIN cycles

DOUT

CLKIN

High-side supply undervoltage

DOUT

DIAG

Power-up

Normal

Operation

Normal

Operation

18

AMC3306M25

SBAS996 – MAY 2020

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Feature Description (continued)

7.3.6 Diagnostic Output

As shown in Figure 12, the open-drain DIAG pin can be monitored to confirm the device is operational, and the

output data are valid. During power-up, the DIAG pin is actively held low until the high-side supply is in regulation

and the modulator starts outputting data. The DIAG pin is actively pulled low if:

•

The low-side does not receive data from the high-side (for example, because of a loss of power on the high-

side). The modulator itself outputs a constant bitstream of logic 0's in this case, that is, the DOUT pin is

permanently low.

•

The high-side DC/DC output voltage (DCDC_OUT) or the high-side LDO output voltage (HLDO_OUT) drop

below their respective undervoltage detection thresholds (brown-out). In this case, the low-side may still

receive data from the high-side but the data may not be valid. The modulator itself outputs a constant

bitstream of logic 0's in this case, that is, the DOUT pin is permanently low.

Figure 12. DIAG and Fail-Safe Output of the AMC3306M25

7.4 Device Functional Modes

7.4.1 Output Behavior in Case of a High-Side Supply Failure

The AMC3306M25 provides a fail-safe output that ensures that the output DOUT of the device offers a constant

bitstream of logic 0's in case the integrated DC/DC converter output voltage is below the undervoltage detection

threshold. The Diagnostic Output section provides for more information.

7.4.2 Output Behavior in Case of a Full-Scale Input

device generates a single one or zero every 128 bits at DOUT, depending on the actual polarity of the signal

being sensed. In this way, detecting a valid full-scale input signal is possible on the system level.

Figure 13. Full-Scale Output of the AMC3306M25