[Nerull]

I have a question. I'm making my DAC and I've come upon a problem. Based on what I've seen in the datasheet of the PCM1792 (by TI) it requires 5 volts for the analog supply section. Do I plug 5 volts in, regardless of current, or do I have to step down the current *using a resistor, I s'pose* to make it down to about 30-40 some mA. But does that matter? Will it take in current and just step them down inside the chip?

~Tom

 

[Garbz]

Umm I think you missunderstand how powersupplies work.

You provide the voltage it sucks the current. I.e. the Analogue supply requires 5v. So you give it a connection of 5v and GND. The chip will then draw current depending on how much it needs. If it's idleing in reset mode then the current draw will be in the microAmp range, when it's working it'll be higher in the milliAmp range.

What you need to make sure is that the chip isn't starved of current. So if you run your analogue section of the DAC chip from it's own 5v line the powersupply must be able to supply at least the maximum rated current in the DAC's datasheet. However if the 5v supply is shared say with output opamps (which it shouldn't if you're going for high quality sound) then your powersupply needs to be able to supply enough current for all the chips at their maximum rating.

The easy way to visualise something like this is to picture heaters plugged in to the wall socket. In Australia our mains runs at 240v / 10A.

If I plug a 1800 watt heater in it will use 7.5A. If I plug a 2400watt heater in it will use all 10A. Plug them both in at the same time and I'll trip the master circuit breaker which is set to go off when the 10A is exceeded on that line.

Powersupplies are a bit more delecate. If you exceed the current rating depending on it's design either the regulator will shutdown because of overload protection, burn out, or in non-regulated designs it's usually the torroid which melts.