MSP430FR2355: 4-20mA current loop using SAC

U-SK

Genius 5840 points

Part Number: MSP430FR2355

Hello.

Are there any measured data about linearity of opamp in SAC?

I am using SAC-L3 in 4-20mA current loop.

In my custom board, SAC1 is used as DAC mode and SAC1 is used as OPA mode like below reference design.

https://www.tij.co.jp/jp/lit/ug/jaju551/jaju551.pdf?ts=1592458738032&ref_url=https%253A%252F%252Fwww.tij.co.jp%252Ftool%252Fjp%252FTIDM-01000

But there is 2-3% error in OPA1OUT voltage from ideal value.

These errors are below or above the ideal value for a cubic curve and no linearity is seen.

DACOUT(OPA3OUT) has almost no error from the ideal value and has linearity.

Is there any solution?

Regards,

U-SK

over 5 years ago

0 Xiaodong LI over 5 years ago

TI__Mastermind 23355 points

Hi U-SK

Thanks for your post! May I confirm the below items:

SAC3 is used as DAC mode and SAC1 is used as OPA mode?

which board you are using on this test?

0 U-SK over 5 years ago in reply to Xiaodong LI

Genius 5840 points

Hi Xiaodong Li,

Thank you for your reply.

Sorry for my typo.

Yes, SAC3 is used as DAC mode and SAC1 is used as OPA mode.

Our custom bard is used for this test.

Regards,

U-SK

0 Xiaodong LI over 5 years ago in reply to U-SK

TI__Mastermind 23355 points

Hi U-SK

For isolate the issue, I propose we can consider using the simpler code (FR2355 code example msp430fr235x_SAC_L3_07.c or the MSP-EXP430FR2355 software examples) on the same custom bard to check if there is still 2-3% error in OPA1OUT or not. Thanks!

0 Xiaodong LI over 5 years ago in reply to Xiaodong LI

TI__Mastermind 23355 points

Hi U-SK

May I know if there is any update on the checking using the simple code (code example)? Thanks!

**Attention** This is a public forum

MSP low-power microcontrollers

MSP low-power microcontroller forum

MSP430FR2355: 4-20mA current loop using SAC