All the DAC output channels remain in a high-impedance state (Hi-Z) when VDD is off. Figure 7-9 shows a simplified schematic of the DACx300x used in a voltage-margining application. Series resistor RS is required in voltage-output mode, but is optional in current-output mode. Almost all linear regulators and DC/DC converters have a feedback voltage of ≤ 1.25 V. The low-leakage currents at the outputs are maintained for VFB of ≤ 1.25 V. Thus, for all practical purposes, the DAC outputs appear as Hi-Z when VDD of the DAC is off in voltage margining and scaling applications. This feature allows for seamless integration of the DACx300x into a system without any need for additional power-supply sequencing for the DAC.
The DAC channels power down to Hi-Z at boot up. The outputs can power up with a preprogrammed code that corresponds to the nominal output of the DC/DC converter or the linear regulator. This feature allows for smooth power up and power down of the DAC without impacting the feedback loop of the DC/DC converter or the linear regulator.
Table 7-18 shows how the GPIO pin of the DACx300x can be configured as a PROTECT function. PROTECT takes the DAC outputs to a predictable state with a slewed or direct transition. This function is useful in systems where a fault condition (such as a brownout), a subsystem failure, or a software crash requires that the DAC outputs reach a predefined state without the involvement of a processor. The detected event can be fed to the GPIO pin that is configured as the PROTECT input. The PROTECT function can also be triggered using the PROTECT bit in the COMMON-TRIGGER register. Table 7-4 shows how to configure the behavior of the PROTECT function in the PROTECT-CONFIG field in the DEVICE-MODE-CONFIG register.
|00||Switch to Hi-Z power-down (no slew).|
|01||Switch to DAC code stored in NVM (no slew) and then switch to Hi-Z power-down.|
|10||Slew to margin-low code and then switch to Hi-Z power-down.|
|11||Slew to margin-high code and then switch to Hi-Z power-down.|