ADC reference

[togrady]

Posted on January 03, 2009 at 14:39

ADC reference

[obtronix]

Posted on May 17, 2011 at 12:19

Quote:

On 11-12-2007 at 13:19, Anonymous wrote: Thanks obtronix. I only need whatever current the STM VDDA pin takes plus about 200uA for other analog stuff. The LM4132 looks like an interesting part. The quiescent current is a little high (60uA)-- ideally I would like something under 30uA. I wonder how much current VDDA on the STM32 requires? Maybe I could put the VDDA regulator in shut down mode when the processor is in standby mode. If I could do this the quiescent current would not matter. Regards Trevor I guess I was wondering how fast are you going to run the STM32? If only 1 Mhz, then it takes only a few mA of current and any precision reference will work, if you are running it at 72Mhz, then you will need 50mA. the VDDA regulator is shut down automatically in standby mode

[togrady]

Posted on May 17, 2011 at 12:19

Can I run VDD (digital) from 3.6V and supply VDDA (analog) with 2.5 volts from a precision reference. Is it possible to have VDD and VDDA at different voltages like this? I can't find anywhere how much current VDDA will take but I'm sure it can't be more than a few mA.

I'm spending the majority of the time in standby mode therefore it would be nice to maybe switch off VDDA when in standby mode. Is this possible? Regards Trevor [ This message was edited by: togrady on 13-12-2007 14:08 ]

[togrady]

Posted on May 17, 2011 at 12:19

repeat deleted

[ This message was edited by: togrady on 13-12-2007 12:09 ]

[obtronix]

Posted on May 17, 2011 at 12:19

Quote:

On 12-12-2007 at 18:15, Anonymous wrote: Can I run VDD (digital) from 3.6V and supply VDDA (analog) with 2.5 volts from a precision reference. Is it possible to have VDD and VDDA at different voltages like this? I can't find anywhere how much current VDDA will take but I'm sure it can't be more than a few mA. I'm spending the majority of the time in standby mode therefore it would be nice to maybe switch off VDDA when in standby mode. Is this possible? Regards Trevor [ This message was edited by: togrady on 13-12-2007 14:08 ] no the part will be destoyed if |VDDA-VDD| >.05 volts, see table 4

[gkruger]

Posted on May 17, 2011 at 12:19

Quote:

no the part will be destoyed if |VDDA-VDD| >.05 volts, see table 4

Hi obtronix, Are you sure that VDDA cannot be different from VDD, I had a look at the datasheet and can see that |�?VDDx| In the STM32 Reference Manual, in table 65 they mention the following: 2.4V ≤ VDDA ≤ VDD (3.6V) Thanks, Gert

[obtronix]

Posted on May 17, 2011 at 12:19

Quote:

On 08-01-2008 at 10:12, Anonymous wrote:

Quote:

no the part will be destoyed if |VDDA-VDD| >.05 volts, see table 4

Hi obtronix, Are you sure that VDDA cannot be different from VDD, I had a look at the datasheet and can see that |�?VDDx| In the STM32 Reference Manual, in table 65 they mention the following: 2.4V ≤ VDDA ≤ VDD (3.6V) Thanks, Gert You mean table 48? Analog power supply equal to VDD and 2.4 V ≤ VDDA ≤ VDD (3.6 V) The first line says they must be equal, the second that VDDA must be above 2.4V

[gkruger]

Posted on May 17, 2011 at 12:19

Quote:

You mean table 48?

Analog power supply equal to VDD and 2.4 V ≤ VDDA ≤ VDD (3.6 V) The first line says they must be equal, the second that VDDA must be above 2.4V Hi obtronix, Conveniently missed that first line, must admit that the VDDA ≤ VDD is a bit misleading. I must be using an older reference manual as my table numbers are all different (UM0306), will check for latest. Thanks for the help, lucky that I spotted your post as I almost made a costly mistake 🙂 Cheers, Gert

[obogush]

Posted on May 17, 2011 at 12:19

Hi everyone,

Actually, the difference between VDDA and VDD can be more than 50mV, see the newest (V9) revision of the datasheet (p.32): ''It is recommended to power VDD and VDDA from the same source. A maximum difference of 300 mV between VDD and VDDA can be tolerated during power-up and operation.'' The major reason they must be connected or at least track each other is that both: reset and PVD sensors are connected ONLY to VDDA, see p.16. In my opinion, it's very inconvenient: the chip should reset itself if either VDD or VDDA voltage goes down. However, it is how this chip is built. It would be nice to hear from Moderator regarding this issue. Regards, Olek

[dir1]

Posted on May 17, 2011 at 12:19

In my oppinion the connection Vref and Vdda in 36, 48 and 64 pins STM32 is really bad idea. If ADC in 100pins STM32F103VB during my tests was very accurate and stable (Vdd and Vdda = 3,3V Vref = 2,5V from ADR391) then LSBs in 48 pins STM32F103C8 was flying. But after few days I found a spill-way. It's 3V shunt voltage references ADR530 is connected to Vdda and R=60 Ohm between Vdda=3V and Vdd=3,3V. I place 10uF ceramic on Vdd and 1uF ceramic on Vdda. The flying LSBs was stopped but it did not influence on functionality POR/PDR and PVD.