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MCP4725 has internal reference voltage which is equals to VCC:

VDD is the power supply pin for the device. The voltage at the VDD pin is used as the supply input as well as the DAC reference input. The power supply at the VDD pin should be clean as possible for a good DAC performance.

Also it needs 50mA of current:

I want to use one LM4040AIZ 4096V reference voltage as power supply for three DACs but the forward current of LM4040 is only 10mA.

So I need LM4040 to provide at least 150mA, How can I achieve that much of current with only one LM4040?

* MCP4725 and LM4040 are the only parts that I have access to.

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You have made the common mistake of misreading absolute maximum ratings and assuming that these are normal operational values.

The supply current taken by the DAC will be a fraction of that stated in the max rating table. Read the data sheet again.

As early as pg 3 the supply current is stated as being no more than 400 uA.

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  • \$\begingroup\$ Supply current: 210uA; so LM4040 is capable of driving 3 MCP4725s? I just want to be sure, need your approval. please. \$\endgroup\$ – ElectronSurf Nov 9 '19 at 14:31
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    \$\begingroup\$ It’s capable but it might produce too much variation in the reference voltage. The 4040’s reverse dynamic impedance and the possible variations in circuit current need to be calculated and then you need to figure out if a 4040 ref is good enough. \$\endgroup\$ – Andy aka Nov 9 '19 at 14:34
  • \$\begingroup\$ I don't have a clue what "reverse dynamic impedance" is! possible variation in circuit current is the current DAC might draw by it's output? \$\endgroup\$ – ElectronSurf Nov 9 '19 at 14:37
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    \$\begingroup\$ If you had a perfect zener with zero impedance, it won’t matter if the zener current is 1 mA or 100 mA. The zener voltage will remain the same. Now, make that perfect zener imperfect by adding 0.3 ohms in series and then ask yourself how much the voltage changes when the load current changes. \$\endgroup\$ – Andy aka Nov 9 '19 at 14:40
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    \$\begingroup\$ You're a great teacher, thank you. \$\endgroup\$ – ElectronSurf Nov 9 '19 at 14:42

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