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I'm reading the datasheet of this DAC. Page 27 states:

In many industrial process control applications, it is vital that the output voltage be controlled during power-up and during brownout conditions.

What are "brownout conditions"? Why is it "vital" that the output voltage be controlled during brownout conditions?

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A brown-out is a short dip in the power supply. Many microcontrollers have brown-out detection on-chip, often, like in the Atmel AVR, with programmable threshold levels. When a brown-out occurs the microcontroller will be reset.

This may seem a bit drastic, but it's a question of reliability, and safety. If just one of those thousand of gates would lock due to a too low voltage it may lock up the complete controller, or have it go bananas, that it still runs, but produces nonsensical results and performs ditto actions. You don't want that, especially not where the microcontroller controls industrial equipment. That's why a brown-out situation always has to be responded to predictably. The DAC does this by shutting the outputs off, which you can expect to be the least harmful behavior.

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    \$\begingroup\$ +1! I had forgot to correctly implement brownout detection in my first home automation board and once during a thunderstorm mains voltage dropped from 230 to 90VAC for a handful of mS. The power controller crashed with all control channels on, leaving all light and appliances switched on for hours, but still responded to the microcontroller in a reasonable way so no alert were generated. \$\endgroup\$ – Axeman Aug 10 '12 at 13:41
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    \$\begingroup\$ Hairy microcontroller ? \$\endgroup\$ – Rocketmagnet Aug 10 '12 at 13:43
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    \$\begingroup\$ @Rocket - I didn't get it! Fixed :-) \$\endgroup\$ – stevenvh Aug 10 '12 at 14:06
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A brownout is a droop in the power supply voltage, not all the way down to zero, but well below the nominal minium.

For electronic components (especially complex chips like microcontrollers) a brownout is a power voltage level between the minimum reqired for normal operation, but above the level at which the chip does not work at all. In this dangerous in-between zone 'anything' can happen. Most datasheets specify a maximum duration for the rise from some very low level (let's say 0.8V for a 5V chip) to the minimum operational level.

For industrial applications 'anything can happen' is often not an acceptable situation. (Imagine exploding chemical reactors etc.) Hence the need for brownout-reset chips, power regulator chips with a power-good output, controlled sequencing of power supply lines, etc.

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    \$\begingroup\$ For me the word "surge" suggests that the power supply is above the nominal maximal. \$\endgroup\$ – Randomblue Aug 10 '12 at 13:29

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