The DACx0502 family of devices includes a power-on reset function that controls the output voltage at power up. After the VDD supply has been established, a POR event is issued. The POR causes all registers to initialize to default values, and communication with the device is valid only after a 250-µs, power-on-reset delay. The default value for all DACs is zero code if RSTSEL = 0, and midscale code if RSTSEL = 1. Each DAC channel remains at the power-up voltage until a valid command is written to a channel.
When the device powers up, a POR circuit sets the device to the default mode. The POR circuit requires specific VDD levels, as indicated in Figure 57, in order to make sure that the internal capacitors discharge and reset the device on power up. In order to make sure that a POR occurs, VDD must be less than 0.7 V for at least 1 ms. When VDD drops to less than 2.2 V but remains greater than 0.7 V (shown as the undefined region), the device may or may not reset under all specified temperature and power-supply conditions. In this case, initiate a POR. When VDD remains greater than 2.2 V, a POR does not occur.