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IO limit voltage of STM32F303RCT6

Lin Zi
Associate II
Posted on June 29, 2017 at 13:50

Hello ST engineers,

According to the MCU (STM30F303RCT6) datasheet, the absolute maximum rating of IO's Vin is 4.0V (page 56).

In our application, operating voltage is 3.3V (Vdd=Vdda=3.3V), but the input voltage of PA0 and PA1 (they are used as ADC function, ADC1_IN1 and ADC2_IN2 respectively) can up to and remain at about 3.75V.

My question is, in this case,

1), will both IO ports of the MCU be damaged and cannot be used again?

2), or both two IO ports just cannot work properly, but once the input voltage is reduced to less than 3.6V (general operating condition, Vdda+0.3V, page58), they can return to work normally?

Thanks in advance.

1 ACCEPTED SOLUTION

Accepted Solutions
Khouloud GARSI
Lead II
Posted on June 29, 2017 at 17:20

Hi

dajiangyou_sp

,

  • The maximum 'Input voltage on TTa pins' is 4V (table21): Exposure to maximum rating conditions may affect the device's reliability and cause permanent damage to the device.Since you reach 3.75V (max) on your application, you're not violating the absolute maximum ratings. Thus, the pins will not be damaged.
  • On the other hand, for the TTa I/Os, the maximum input voltage should be VDD+0.3V(table24).

In our application, operating voltage is 3.3V (Vdd=Vdda=3.3V), but the input voltage of PA0 and PA1 (they are used as ADC function, ADC1_IN1 and ADC2_IN2 respectively) can up to and remain at about 3.75V.

-> In your application, those pins may reach 3.75V: This is out of specification -> Results are not guaranteed.

To have reliable results, you should respect the specification: -0.3V <= I/O input voltage <= vdd+0.3v

Khouloud.

View solution in original post

8 REPLIES 8
Khouloud GARSI
Lead II
Posted on June 29, 2017 at 17:20

Hi

dajiangyou_sp

,

  • The maximum 'Input voltage on TTa pins' is 4V (table21): Exposure to maximum rating conditions may affect the device's reliability and cause permanent damage to the device.Since you reach 3.75V (max) on your application, you're not violating the absolute maximum ratings. Thus, the pins will not be damaged.
  • On the other hand, for the TTa I/Os, the maximum input voltage should be VDD+0.3V(table24).

In our application, operating voltage is 3.3V (Vdd=Vdda=3.3V), but the input voltage of PA0 and PA1 (they are used as ADC function, ADC1_IN1 and ADC2_IN2 respectively) can up to and remain at about 3.75V.

-> In your application, those pins may reach 3.75V: This is out of specification -> Results are not guaranteed.

To have reliable results, you should respect the specification: -0.3V <= I/O input voltage <= vdd+0.3v

Khouloud.

Zt Liu
Senior III
Posted on June 29, 2017 at 17:35

Why don't you just re-scale that signal, using a op-amp and divider, by a factor 2/3,

then setup a good 2.5 Voltage Reference for VRef or VDDA(if your Ref Volt IC has some driving power).

If so, your full scale voltage is simply 3.75/3*2 = 2.5 = VRef or VDDA, 

Isn't it nice for you? 

By the way, even if it will not damage your io,

once your ADC_INx got voltage > VDDA or VRef, the ADC  always gives you 4095.

You'll never want this.

Posted on June 30, 2017 at 04:22

Hello Khouloud,

Thank you very much, you answer is exactly what I want.

Best regards!

Posted on June 30, 2017 at 04:38

Hello Zhitai,

Thank you for reply.

Yes, you are right. we also did this like you said:

normally operation, external analog input voltage is 10V, after a resistor divider (1/4) we get a 2.5V to ADC, this is no problem. And at the ADC port, we also put a clamping diode to 3.3V.

but, there is a risk is that our customer may connect a higher external voltage, such as 24V. then after divider and clamping diode, the input signal voltage into ADC up to 3.7V.

so this is what I worried about and why to check if there is risk to damage the IO.

Posted on June 30, 2017 at 07:37

What about simply place a clamped diode in the beginning of your external voltage?

(note that it would lower the input impedance)

Posted on June 30, 2017 at 08:26

Hello Zhitai,

how to do?

in our circuit, the cathode of the clamping diode is connected with 3.3V, while the anode connected with the signal after resistor divider.

Harry Blake
Associate II
Posted on May 10, 2018 at 11:57

Hey I wanted to connect

https://store.ncd.io/product/4-channel-i2c-0-10v-analog-to-digital-converter-with-i2c-interface/

with STM32F303 and monitor the readings of pressure sensor please suggest me the best way to communicate with 0-10v reading of ADC with STM which is operated with 3.3V power.

your intel will be very helpful

Posted on May 11, 2018 at 17:25

Hey Harry, 

I just looked the link.

The only problem you got is 3.3V/5V I2C level shift. 

This link may help you.

https://www.nxp.com/docs/en/application-note/AN10441.pdf

 

or you can some dedicated IC for level shifting. 

Perhaps 

you should start another thread. 

Good Luck.