Notes on absolute maximum ratings of ICs (such as the MSP430)

The major components on a WiSense node include the MSP430G2955 micro, the radio (CC1101 or  CC2520), serial EEPROM (AT24MAC602), the LM75B temperature sensor and the TSL45315 ambient light sensor. You are of course free to interface any compatible sensor to a WiSense node.

Each of the components listed above has an absolute maximum supply voltage rating and a recommended operating voltage range. I have listed them below.

      Component                  Absolute max supply voltage             Recommended range

  • MSP430G2955                      -0.3 to 4.1 V                                           1.8   to 3.6 V
  • CC1101                                 -0.3 to 3.9 V                                           1.8   to 3.6 V
  • AT24MAC602                        -0.1 to 7.0 V                                           1.7  to 5.5 V
  • LM75B                                   -0.3 to 6.0 V                                           2.8  to 5.5 V
  • TSL45315                               0.0 to 4.5 V                                           2.3  to 3.3 V

The datasheet for the MSP430G2955 has this note in relation to the absolute max supply voltage which can be applied to this IC (-0.3 to 4.1 V).

Stresses beyond those listed under ‘absolute maximum ratings’ may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.”

I found a post by a TI employee on TI E2E (http://e2e.ti.com/support/microcontrollers/msp430/f/166/t/170241.aspx)  (copied below).

“If you’re just playing around with the part and not planning to go to production with the design, 3.7V is probably OK.  However, officially we won’t guarantee anything over 3.6V, as it can degrade the part’s performance.  So for production, you want to use a regulator and keep Vcc under 3.6V.”

This matches the note in the datasheet. Even though 4.1 V is the absolute max voltage the IC can handle without permanent damage, this does not imply that you should operate the part outside the recommended operating supply voltage (1.8 V to 3.6 V).

The important takeaway is to operate any component only within the recommended operating voltage range as specified in the component’s data sheet. This should be true for most components available on the market today.

Surprisingly, the 3.6 V limit for the MSP430G2955 does not mean that the part will always get damaged if the applied voltage exceeds 3.6 V.  I have reversed power and ground connections to WiSense nodes many times. The nodes always worked after I corrected my mistake. According to TI, I was just lucky. It is possible that the MSP430 did get damaged but I do not know it yet. We are going to add a reverse protection mechanism asap to WiSense nodes.

When you have multiple components with different operating voltage requirements and a single supply rail for all the components (which is true for WiSense nodes) you need to make sure that your operating voltage satisfies the recommended operating voltage range of each component. According to the table (above), the TSL45315 ambient light sensor has a max recommended operating voltage of 3.3 V.  The LM75B’s recommended lowest operating voltage is 2.8 V. This provides the recommended operating voltage range for WiSense nodes (2.8 V to 3.3 V).  If you interface any other component to a WiSense node (sensors for example),  you may have to adjust the operating voltage range (2.8 to 3.3 V) further depending on the component’s operating voltage range.

Posted on November 27, 2014, in Uncategorized. Bookmark the permalink. 1 Comment.

  1. Working with TI LaunchPad, I have reversed ground and Vcc as well. At best, the LaunchPad starts heating up! When I corrected my mistake, things worked as expected.

    A few days ago on a TI Launchpad, I was trying out analog input. Since I didn’t really have an analog input to test, I connected the pin P6.0 to 3V available on the LaunchPad. No problem. Out of curiosity, I then connected it to 5V, also available on the LaunchPad. Boom! LaunchPad crashed. Now I cannot use P6.0 for analog input (and maybe for other pin functions as well). What I am not sure is if the MSP is fried or only the LaunchPad circuitry is fried.

    Moral: don’t connect to anything above 3.6V.

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