LPC5536: on DAC current sources (ZTC, PTAT)

[danielholala]

Hello,

I'm currently evaluating the DAC of LPC5536-EVK.

After reading the reference manual, it's still not clear to me what to do with DAC's "current sources":

48.1.4. To initialize the DAC module:
...

• Enable VREF module (PDRUNCFGCLR0[PDEN_VREF] = 1) in PMC register. DAC PTAT and ZTC current sources comes from VREF module.

This does not explicitly state to enable these current sources. Do I have to enable them, maybe both of them?

This is a valid question as these current sources can be enabled separately in Global Control register (GCR):

Bit 21 IREF_ZTC_EXT_SEL
External On-Chip ZTC Current Reference Select
Selects the external ZTC current reference, which is from the VREF module. See the Chip-specific section for more information.
0 - Not selected
1 - Selected

Bit 20 IREF_PTAT_EXT_SEL
External On-Chip PTAT Current Reference Select
Selects the external PTAT current reference, which is from the VREF module. See the Chip-specific section for more information.
0 - Not selected
1 - Selected

*rant* Here, the current source is called "current reference". What has driven the author to suddenly change the terminology? This is a technical document. Choose your term and stick to it! *rant end*

Further, the chip-specific section does not contain more information on these current sources. Where is it?

What is the advantage / disadvantage of PTAT or ZTC current source? The product data sheet is silent about their characteristics.

Please advise!
Thanks.
Daniel

[danielholala]

Note: When configuring DAC using Peripherals Tool, it does not require VREF to be configured. I presume this is a bug. Instead, Peripherals Tool should show a warning / error message in the Problems window to this end.

[danielholala]

Regarding enabling VREF, this issue has been fixed in MCUXpresso IDE 25.6.

[danielholala]

@xiangjun_rong , I agree completely. 

Thanks for the slides. However, I did not find any information on ZTC or PTAT current sources.

Could you forward the question to a Systems Engineer who is concerned with DAC?

Best regards,
Daniel

[xiangjun_rong]

Hi,

I have to say that the Reference manual of LPC553x is not good, there is not a clear description about the ZTC and PTAT current source, including the mechanism, application, the relationship with DAC...

I attach an training about the Vref and DAC, hope it can shed a light on the two modules.

BR

XiangJun Rong