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why the DAC/ADC board needs so many DC powers? #385

Closed ypzhong closed 7 years ago

ypzhong commented 8 years ago

Hi,

I'm curious why the DAC/ADC board needs so many different DC powers? I read the document of the voltage regulators, it looks like the input voltage can be much higher than the expected output voltage, for example, we can input 5.4V to all the power pins and the voltage regulators will output 1.2V, 1.8V, 2.5V, 3.2V, 5.0V etc respectively. So why do we use 1.6V, 2.2V, 2.9V, 3.7V, 5.4V DC power supply to power each pin separately? Is there a good reason to do so? Thanks.

Youpeng

ejeffrey commented 8 years ago

There are basically two reasons for this.

The first is to minimize power dissipation in the regulators. The idea is that temperature change is a major cause of drift, so if you have a bunch of regulators dissipating a few watts each on the PCB, that is potentially bad.

The second is because some of the power rails are analog supplies and some are digital. By using separate supplies for each voltage rail, we keep those separated.

Check the max power dissipation of the regulators, as long as that is OK the boards should work with the single supply, but keep in mind that performance may be changed.

Evan

On Wed, Nov 2, 2016 at 2:45 PM, Youpeng Zhong notifications@github.com wrote:

Hi,

I'm curious why the DAC/ADC board needs so many different DC powers? I read the document of the voltage regulators, it looks like the input voltage can be much higher than the expected output voltage, for example, we can input 5.4V to all the power pins and the voltage regulators will output 1.2V, 1.8V, 2.5V, 3.2V, 5.0V etc respectively. So why do we use 1.6V, 2.2V, 2.9V, 3.7V, 5.4V DC power supply to power each pin separately? Is there a good reason to do so? Thanks.

Youpeng

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ypzhong commented 8 years ago

@ejeffrey Thanks for your reply. I looked at the document of the regulators, it seems that the regulator heat dissipation is IOUT(V_IN-V_OUT)+I_GND_I_IN, so the larger the input/output voltage differs the more heat the chip dissipates.