MSP430G2553: Device is working without Vcc

Chase Jeong

Genius 4660 points

Part Number: MSP430G2553

Hello TI experts,

My customer now tests MSP430G2553 for their new product, and they found one problem.

- they will use ADC function, so they applied 3.3V to pin4 for test.

- this MCU is working even they did not apply DVCC and AVCC.

- they tested with TI basic examples ; Software toggle and Basic Clock. it was same.

is it normal operation? or definitely a problem?

please check this issue. Thanks.

Best regards,

Chase

over 2 years ago

+1 Keith Barkley over 2 years ago

Guru 35570 points

"is it normal operation? or definitely a problem?"

Yes, and Yes.

You can power the chip via the ESD diodes on each pin. But since the voltage isn't controlled you can put the CPU into a weird state if the voltage too low.

You need to prevent voltage from reaching the chip if the power is off, or keep power on and put the chip into deep sleep. or hold reset until the power is on.

0 SY Yoon over 2 years ago in reply to Keith Barkley

Genius 3380 points

I have some question.

I don't understand how it works without VCC

ADC port or other pins are connected with VCC internally?

+1 Keith Barkley over 2 years ago in reply to SY Yoon

Guru 35570 points

All the pins have ESD protection diodes that go from the pin to the VDD rail. In normal operation, they are reverse biased and have little effect on the chip. If you apply a voltage to a pin with no Vdd applied, that diode becomes forward biased allowing current to flow into Vdd turning on the chip.

0 Chase Jeong over 2 years ago in reply to Keith Barkley

Genius 4660 points

Dear Keith,

Thank you for your support.

It does make sense, cause my customer said that he can see about 2.6V on Vcc when he apply 3.3V through P4 or P3.

so all the MSP430 series have same issue, applying voltage on all GPIO pins?

Best regards,

Chase

+1 Keith Barkley over 2 years ago in reply to Chase Jeong

Guru 35570 points

Practically every CMOS chip in existence, even the custom one where I first came across this issue.

+1 Cash Hao11 over 2 years ago

TI__Mastermind 27465 points

Hi Chase,

Just a reminder. Like Keith said please prevent powering the device not through the VCC pin.

Best regards,

Cash Hao

+1 Keith Barkley over 2 years ago

Guru 35570 points

Just for the record, Applying more than .3 V to a pin when VDD is off ( 0V) violates the Absolute Maximum Ratings:

0 Chase Jeong over 2 years ago in reply to Keith Barkley

Genius 4660 points

Dear Keith and Cash,

Thank you for your support. I will discuss it with my customer.

Best regards,

Chase

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MSP430G2553: Device is working without Vcc