LPC5536JBD100 DAC0 questions

[Bela1]

Ladies and Gentlemen,

I set up DAC0 with external reference (3V on Pin15), buffer mode, clock is FRO1MHz divided by 8.

When I set DAC0 Data less than about 0x700, the output is just noise, like it would float.

When the data is between 0x700 and 0xFFF, then the output is a concrete voltage, no noise, doesn't float.

What can be the reason of this?

Additionally: how much is the voltage range of DAC0 output? Shouldn't it go from 0V up to the reference? In my case, it is 3V. My experience is, that with DAC0 DATA = 0xFFF, the output voltage from DAC0 is only 1.35V. I cannot find any setting, which halves the output voltage, what can be the reason of this?

There is no load on the output of DAC0 (pin31).

[Bela1 · Accepted solution]

Problem solved:

Although it is not written in the Reference Manual chapter 48.1.4 (DAC Chip-specific initialization), it is necessary to enable the buffer, too.

DAC0 -> GCR |= BUF_SPD_CTRL ; // buffer opamp low power mode, bit 23

DAC0 -> GCR |= BUF_EN ; // enable opamp buffer, bit 17

Now, the DAC goes from 0 up to Vref, the output is driven to a concrete voltage, never floats.

It would be practical, to complete the chapter 48.1.4 with the necessary "buffer enable".