The AMC131M02 does not generate conversion data automatically after power-up because the integrated DC/DC converter is disabled initially. For the ADC to operate, the DC/DC converter must be enabled after power-up, and a stable supply voltage at the HLDO_OUT pin must be established that serves as the power supply for the circuitry on the secondary (high) side.

A recommended procedure for powering up the AMC131M02 is described in this section. Figure 8-19 depicts a timing diagram for the device behavior when this recommended sequence is used. Figure 8-17 provides a flow diagram that displays the recommended sequence in a graphical form.

Follow these steps to ensure a correct start-up behavior at power-up:

• Power up the DVDD supply.
• The transition of DRDY from low to high indicates a valid supply voltage on the primary side is established, and also indicates the SPI interface is ready for communication.
• Configure the clock divider by setting the CLK_DIV[1:0] bits in the CLOCK register as needed.
• Configure the modulator clock frequency by setting the DCDC_FREQ[3:0] bits in the DCDC_CTRL register; see the Clocking and Power ModesClocking and Power ModesClocking and Power ModesClocking and Power Modes section for details.
• Enable the DC/DC converter by setting the DCDC_EN bit in the DCDC_CTRL register to 1b.
• Configure all other registers of the AMC131M02 before the external clock is applied to the CLKIN pin.
• Provide the main clock at the CLKIN input to start operation of the integrated DC/DC converter, and to make sure that the secondary power supply at the HLDO_OUT pin is generated.
• The transition of the SEC_FAIL bit in the STATUS register from high to low indicates that the secondary power supply at the HLDO_OUT pin is established and the ADC conversion data output is valid. Confirm device operation by reading the SEC_FAIL bit, and verify that this bit is set to 0b, before reading any conversion data from the ADC. There are two options for reading the SEC_FAIL bit in the STATUS register: sending a NULL command results in a response including the STATUS word, or sending a register read command to read the STATUS register. The SEC_FAIL bit is a latched bit; therefore, at least two read commands are required to confirm that this bit transitioned from high to low; the first read command clears the logic high value that is latched during device power-up. Use the second read command to verify that the SEC_FAIL bit is set to 0b, indicating that the secondary supply is valid. If the SEC_FAIL bit still reads 1b as a result of the second read command, continue reading the SEC_FAIL bit until this bit reads 0b before reading any conversion data from the ADC.

Regarding the conversion data after power-up, pay attention to the following:

• The high-to-low transition of DRDY indicates that new conversion data are available. As given in Figure 8-19, ADC data are only valid if the SEC_FAIL reads 0b during the conversion period. The first two conversion results shown in Figure 8-19, represent invalid data.
• When the ADC generates valid data, the digital filter must settle, as described in the SINC³ and SINC³ + SINC¹ Filter section. Two subsequent conversion results illustrated in Figure 8-19 are unsettled (assuming OSR equals 1024), and the last conversion result shown provides valid and settled data.
• For best control of the conversion timing, especially in a system where multiple devices of the AMC131M02 are used, trigger a synchronization using the SYNC/RESET pin before the host collects conversion data from the ADC. See the SynchronizationSynchronizationSynchronizationSynchronizationSynchronization section for more details regarding how to synchronize the device.

In Figure 8-19, t_{POR_SEC} is the time from enabling the DC/DC converter to the first falling edge of the SEC_FAIL bit, which indicates that the secondary power supply at the HLDO_OUT pin is stable. t_{POR_DVDD} is the time from DVDD supply at 90% to DRDY first rising edge.

Figure 8-16 Start-Up Behavior at Power-Up and Settling Times, OSR = 1024

Figure 8-17 Flow Diagram for Start-Up Procedure at Power-Up