# DAC datasheet - how to read if the DAC can drive my circuit?

#### tysseng

Joined Apr 14, 2013
1
Hi! I am trying to select a DAC that will be connected to a filter circuit. I would prefer NOT to use an additional op amp to buffer the DAC output. The DAC output will be 0-5V. The first cell of the filter looks like this:

Now, looking at two different DACS (one 12bit and one 16bit, this is not really important to the question), I can only find the following about driving capabilities:

In this datasheet it says that all tests have been done with Rload = 5kOhm and output of 4.096V. I am having a hard time to understand exactly how to interpret Rload and what this means - as far as I can read, Rload means a (theoretical/equivalient) resistor from output to GND.

I understand this as "any Rload HIGHER than 5kOhm will be fine", is this correct?

This datasheet says:
"These DACs are capable of driving unbuffered loads of 60 kΩ".

Does this mean that anything LOWER than 60kOhm is not possible without additional buffering? And does this mean that this DAC is unsuitable for directly driving my filter?

Sorry if these questions are stupid...

#### OBW0549

Joined Mar 2, 2015
3,566
Now, looking at two different DACS (one 12bit and one 16bit, this is not really important to the question), I can only find the following about driving capabilities:

In this datasheet it says that all tests have been done with Rload = 5kOhm and output of 4.096V. I am having a hard time to understand exactly how to interpret Rload and what this means - as far as I can read, Rload means a (theoretical/equivalient) resistor from output to GND.

I understand this as "any Rload HIGHER than 5kOhm will be fine", is this correct?

As I read it, the 5 kΩ is simply their test condition under which the various parameters are measured for the data sheet. Certainly, any load resistance higher than that (including your filter, with the component values shown) should be fine.

This datasheet says:
"These DACs are capable of driving unbuffered loads of 60 kΩ".

Does this mean that anything LOWER than 60kOhm is not possible without additional buffering? And does this mean that this DAC is unsuitable for directly driving my filter?
Yes, to both questions. The output of this DAC appears to be directly from its R-2R ladder, without buffering. An external buffer is necessary.

#### Papabravo

Joined Feb 24, 2006
21,225
Your opamp circuit does not show the supply pins so I don't know if you intend for this to be a single or dual supply application. This circuit is going to give you trouble because there is no DC path to Ground on the high impedance inputs. The ability to drive a load depends on the nature of the DAC output. I'll take a closer look and get back to you.

Never mind. I'll go with what Obie says, but I still think you need a DC path to ground for dual supply operation or to Vcc/2 (including a DC path to ground) for single supply operation.
#1 google hit for "do opamp circuits need a DC path to ground"

It is important to note that, just as we found for transistor circuits, one should always provide a DC path to ground for op-amp inputs. Otherwise, charge will build up on the effective capacitance of the inputs and the large gain will convert this voltage (= Q/C) into a large and uncontrolled output voltage offset.

Pay heed young Jedi to the wisdom of the masters.

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#### Irving

Joined Jan 30, 2016
3,880