NXP DesignsのトピックRe: about the S32k144 Vref internal block diagram

about the S32k144 Vref internal block diagram

qiaoqin_wang — Thu, 03 Sep 2020 05:28:38 GMT

i have read the S32K144 datasheet ,but i can't understand about the Vref volateg for ADC,

can you help me to understand it better;

Does the ADC reference voltage VREF come directly from an external power supply, will the MCU chip do the conversion? For example, blood pressure, or other forms?

thanks for you

looking forward your reply

Re: about the S32k144 Vref internal block diagram

qiaoqin_wang — Mon, 07 Sep 2020 03:16:15 GMT

can you help me to understand this confusion, i need to konw this informtaion, so that i can design my schematic better,thanks for you help ,and looking forward your reply.

Re: about the S32k144 Vref internal block diagram

lukaszadrapa — Mon, 07 Sep 2020 08:08:41 GMT

Hi,

yes, you are supposed to connect VREFH to external supply voltage. Notice that the difference between VREFH and VDDA should not be higher than 0.1V, so it means the best way is to use the same supply voltage for both.

And just in case if you are not aware of this app note:

https://www.nxp.com/webapp/Download?colCode=AN5426

Regards,

Lukas

Re: about the S32k144 Vref internal block diagram

qiaoqin_wang — Mon, 07 Sep 2020 09:21:48 GMT

Dear lukaszadrapa

thanks for your replying

but i want to konw the internal bolack diagram for detail about the vref voltage，can you provide it，thanks， for example：when the external supply voltage for the vref，how the MCU internal to change the voltage for the ADC to use，thanks.

Re: about the S32k144 Vref internal block diagram

lukaszadrapa — Tue, 08 Sep 2020 09:46:15 GMT

I'm afraid we do not provide internal block diagram.And I'm not sure if I can understand your question. Could you please provide better explanation?

Regards,

Lukas

Re: about the S32k144 Vref internal block diagram

qiaoqin_wang — Tue, 08 Sep 2020 10:20:54 GMT

Dear lukaszadrapa

sorry， Maybe what I described is not very clear，i will try to descirbed it； thanks for your patience;

because we use the MCU is S32K144,and we use the LDO to supply 5V for the Vref;

we want to konw if we supply 5V voltage for the Vref,if the ADC convert the voltage that use the Vref voltage form the LDO ; (exp: down the voltage for 3.3V ,or high accuracy compoenent to keep the Vref voltage don't change when the external LDO change),so i want to know the internal Vref voltage internal detail block digaram;

formula

1 LSB = (VREFH - VREFL)/2N:

S32K144 block diagram ：

as the below is the Vref，i want to konw the internal detail for the Vref.

Re: about the S32k144 Vref internal block diagram

qiaoqin_wang — Thu, 10 Sep 2020 01:15:29 GMT

Dear lukaszadrapa

could you help me to understand this confusion,thanks for your help and looking forward your reply.

Re: about the S32k144 Vref internal block diagram

lukaszadrapa — Thu, 10 Sep 2020 05:32:25 GMT

Hi,

the reference is used directly. If the Vref is changed, the "1 LSB = (VREFH - VREFL)/2N:" is changed accordingly. If there's a noise on the Vref, the noise will affect also the accuracy. It's responsibility of user to ensure that the voltage is kept constant as much as possible.

Regards,
Lukas

Re: about the S32k144 Vref internal block diagram

qiaoqin_wang — Thu, 10 Sep 2020 11:16:13 GMT

Dear lukaszadrapa

thanks for your so quick reply,and i have undestand ,but i have anthoer question and i need your help

we use the MCU is s32K144,and we want to use the bandgap to monitor the Vref voltgae(Vref)

as the below picture show:

so we want to check :

1. The bandgap channel delivers a fixed 1 V that the voltage doen‘t change,Even if the MCU's power supply changes, its voltage does not change, it is always a constant 1V？

2. whether the bandgap channel voltage will change when the MCU external power supply voltage is lower than a certain value （exp:1.5V )?

Re: about the S32k144 Vref internal block diagram

lukaszadrapa — Fri, 11 Sep 2020 08:14:38 GMT

Hi,

1. yes, that's the nature of bandgap voltage.

2. operating voltage of this device is 2.7V up to 5.5V. If the supply voltage falls below 2.7V, low voltage reset circuit will trigger reset and the device will stay in reset until the voltage is high enough again. So, down to 2.7V it will still work.

Regards,

Lukas

Re: about the S32k144 Vref internal block diagram

qiaoqin_wang — Mon, 14 Sep 2020 01:33:34 GMT

Dear lukaszedrapa

1. yes, that's the nature of bandgap voltage.

WQQ ---this explataion i have understand ,thanks!

WQQ ---I’m still very confused about this explanation. I understand what you mean, when the MCU’s power supply voltage is lower than 2.7V，the MCU will reset，but i want to know that the operating voltage of this device is lower than 2.7V,if the bandgap voltage is still 1.0V ,if the voltage is lower, as low as 0.5V, is the bandgap voltage is still 1.0V ?

thanks for you so patienece explanation,thanks

Regards,

Re: about the S32k144 Vref internal block diagram

lukaszadrapa — Mon, 14 Sep 2020 06:13:31 GMT

Hi,

if the voltage is lower than 2.7V, the device is held in reset. The application is not running and you can't read the bandgap voltage, of course. So, this question doesn't make sense.

If the reset is released (i.e. supply voltage is above 2.7V), the bandgap voltage will meet the specification.

Regards,

Lukas

Re: about the S32k144 Vref internal block diagram

qiaoqin_wang — Mon, 14 Sep 2020 06:22:42 GMT

dear lukaszadrapa

Thank you for replying to me so quickly and patiently, sincerely thank you, hope you have a happy day every day.