topic Re: K10 Vref Factory Trim in Kinetis Microcontrollers

K10 Vref Factory Trim

phil74 — Wed, 07 Dec 2016 14:03:40 GMT

Hello

We’re encountering an issue with VREF on MK10DX128VLH5:

VREF_OUT value (in steady state) is 1.182V whereas on other PCB we have 1.196V.

Conditions:

VREF_TRM[CHOPEN], VREF_SC[]REGEN] and VREF_SC[ICOMPEN] bits are set.

VREF_TRIM[TRIM] is untouched.

So we except to reach datasheet figures (between 1.1915 and 1.1977V).

Datasheet specifies two ranges with factory trim: from 1.915 to 1.1977V or from 1.584 to 1.2376V

Can you give us more details about these two ranges ? What should be the expected range ?

Thanks in advance,

Best regards,

Philippe

Re: K10 Vref Factory Trim

Hui_Ma — Fri, 09 Dec 2016 07:44:09 GMT

I had done a test about VREF_OUT voltage with TWR-K20D50M board:

I modified the VREF_TRM[TRIM] bits value with below measured voltage:

VREF_TRM [TRIM] bits value VREF_OUT voltage(V)

0x23 (default) 1.1918

0x0 (Min.) 1.1740

0x3F(Max.) 1.2058

0x26 1.1932

0x27 1.1940

0x28 1.1946

0x29 1.1950

0x2A 1.1956

0x2B 1.1960

The datasheet provided factory trim value is VREF module could trimmed output voltage range.

In general, customer could not reach this range.

The user trim range is customer could trimmed VREF module close to typical output voltage value 1.195V in full chip operation voltage and temperature range.

As my tested, the trim value 0x29 could get 1.1950V VREF_OUT voltage, which is most close value to 1.195V in my test environment.

In application field, customer should refer user trim range.

Wish it helps.

Have a great day,
Ma Hui
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Re: K10 Vref Factory Trim

phil74 — Fri, 09 Dec 2016 13:59:39 GMT

Hi,

In fact the question is :

Why datasheet specifies two ranges of factory trim:

1 / from 1.915 to 1.1977V

2 / from 1.584 to 1.2376V

Can you explain me the difference between the two ranges in the datasheet regarding these 2 factory trim ?

So, what is the range of VREF_OUT : 1/ or 2/ ?

BR,

Philippe

Re: K10 Vref Factory Trim

Hui_Ma — Mon, 12 Dec 2016 06:04:00 GMT

The datasheet showed Vout value, one is factory trim (show the VREF module output voltage range), the other one is factory trim at nominal VDDA and temperature=25C (show the VERF output voltage range with factory trim value in typical application condition).

In general application, the VREF output voltage should in range of below range.

Customer should refer below parameter:

Wish it helps.

Re: K10 Vref Factory Trim

phil74 — Mon, 12 Dec 2016 10:26:52 GMT

Hello,

So why do we provide factory trim values from 1.584 to 1.2376V?

What is the added value for customer ? or in which case this information is relevant ?

BR,

Philippe

Re: K10 Vref Factory Trim

Hui_Ma — Tue, 13 Dec 2016 01:53:32 GMT

VREF output voltage will modify with operation temperature changed.

The K10 datasheet table 27 shows the full-range (-40 °C~ 105 °C) VREF operation behavior, the factory trim VREF output voltage in range of [1.1584V ~ 1.2376V].

Customer also could check the table 29 about limited range (0 °C~ 50 °C) factory trim VREF output voltage range is in [1.173V ~ 1.225V].

Customer need to trim the VREF output voltage with operation temperature modified.

Wish it helps.

Re: K10 Vref Factory Trim

egoodii — Tue, 13 Dec 2016 12:48:32 GMT

In other words, these digital CPU subsystems are not capable of precision analog voltage generation. Factory-trimmed at 25C to +/-0.23% is +/-3.3% over full temp, +/-2.2% 0to50. You can trim (within a range) at any temperature you like (to +/-0.17%?) and apparently not expect significant 'long term drift', but if you have any temperature RANGE to operate in, you would be better even with just an NCV1117 Vdd regulator (or related part) at +/-2% over load and temp.

Re: K10 Vref Factory Trim

phil74 — Wed, 14 Dec 2016 09:47:41 GMT

Hello,

OK, I understand that voltage will change with temperature.

But spec say that :

Factory trim is automatically loaded at reset.

So, what is the factory trim value automatically loaded at reset.? Is it the one tested at 25°C ?

BR,

Philippe

Re: K10 Vref Factory Trim

egoodii — Wed, 14 Dec 2016 12:38:22 GMT

Certainly -- there is ONLY ONE trim value, and the factory-process is to the specified accuracy (+/-0.23%), and done there at 25C.

What 'error bound' across 'what temperature range' does your product-function require?

Does your part pin-out a separate Vref-input? Is the reference-voltage to be used for input (internal ADC) or output (internal DAC)?