As shown in Figure 7-7, 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. However, the modulator itself outputs a
constant bitstream of logic 0's in this case, meaning that the DOUT pin is
permanently low.