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Original question:

MSP430I2040: Operation of SD24

MSP430I2041: Absolute Maximums of the SD24 +/- Input Pins A0.0 - A3.0

Zachary Anderson
Prodigy 30 points

Part Number: MSP430I2041
Other Parts Discussed in Thread: MSP430I2040, MSP430F6735A, MSP430I2020

Question

What are the absolute max values (positive and negative with respect to AVSS) that we can apply without degrading the msp430i2041 SD24 analog inputs?

Background

The TI Manual for the MSP430i2041 (Ref 1) seems to contradict itself on what the absolute maximum ratings are for the SD24 Channels A0.0+ to A3.0-. In the manual on page 14, the absolute maximum ratings of the MSP430i2041 board are found in table 5.1 Absolute Maximum Ratings.  Under the parameter “Voltage applied to any pin (excluding VCORE, ROSC)” the minimum and maximum voltages are listed as -0.3V and Vcc + 0.3V with reference to Vss (see note 2 of the table).

Vss is not defined later until Table 5.3 Recommended Operating Conditions.  Vss is defined as the Supply Voltage (AVss = DVss = Vss) implying that AVss and DVss are at the same potential such as when they are connected together.

Later on page 22, Table 5-21. SD24 Input Range provides parameters related to the inputs of the SD24.

From this table we can see listed two parameters of interest related to our question, V(i) and V(ic) which are the Absolute input voltage range and the Common-mode input voltage range respectfully.  Their minimum and maximum values are identical.   The maximum is listed as VCC and minimum listed as AVSS – 1.  If we are to assume that AVss = DVss = Vss = GND then these parameters can be interpreted as having a minimum voltage of Vss-1V and a maximum voltage of Vcc.

Table 5.1 and Table 5-21 seem to have conflicting parameters. What is the range for a common mode signal (a signal with reference to AVSS) that can be applied to pins A0.0+ to A3.0- of the SD24 without degrading the SD24 over time?  James Evans with MSP Customer Applications has replied to a number of questions on the site e2eTi.  In response to a question titled “MSP430I2040: Operation of SD24” by Bob Bacon (Ref 2), James answers the following question for Bob:

“Question 1: Does [table 5-21 of the MSP430i2041 datasheet] mean that you can apply negative voltages?

The MSP430i2040 has differential inputs, so yes, you can apply negative inputs (assuming they fall inside the absolute and common-mode input ranges shown in Table 5-21).”

James implies here that you can indeed put a negative voltage as low as AVss – 1 on the input pins of the SD24 and that the absolute parameters from Table 5.1 does not apply to these pins.  He makes no mention of table 5.1. Meaning that a common-mode signal of -1V with reference to Vss could be applied over an extended period of time to the SD24 +/- pins A0.0 to A3.0 without degrading it.

The literature ADC12EU050, Continuous-Time Sigma-Delta (ref 3) seems to weakly support this answer as well.  On page 5, when discussing the model of the CTSD ADC, the author mentions “… the allowable input voltage range [of the CTSD ADC] can be higher than for a SC sampled-input ADC; indeed, the input voltage can even exceed the supply rails.”

Assuming James' answer is correct, then values as low as -1V with reference to AVss can be applied to the pins of the SD24 with out degrading it.  If any of my assumptions are incorrect, please let me know.  But it is still unclear if negative values below -1V which might not operate within the specifications could be applied without long term degradation to the SD24.  For example, imagine our device boots and -3.3V is applied to pins A0.0+ and A0.0- for a few milliseconds before being pulled to 0V; would that degrade the SD24 and MSP430i2041 over time? 

Thus our question is this:

What are the absolute max values (positive and negative with respect to AVSS) that we can apply without degrading the msp430i2041 SD24 analog inputs?

References:

  1. MSP430i204x, MSP430i203x, MSP430i202x Mixed-Signal Microcontrollers Literature Number: SLAS887. (August 2014)
  2. MSP430I2040: Operation of SD24 - MSP low-power microcontroller forum - MSP low-power microcontrollers - TI E2E support forums. (2018). E2e.ti.com. Retrieved May 31, 2022, from https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/707817/msp430i2040-operation-of-sd24
  3. Continuous-Time Sigma-Delta ADCs Literature Number: SNAA098. (January, 2008). Retrieved May 31, 2022, from https://www.ti.com/lit/an/snaa098/snaa098.pdf?ts=1654012558166
  4. MSP430F6735A: SD24 Differential Input, range of Vi,A+ and Vi,A- - MSP low-power microcontroller forum - MSP low-power microcontrollers - TI E2E support forums. (2020). E2e.ti.com. Retrieved May 31, 2022, from https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/913161/msp430f6735a-sd24-differential-input-range-of-vi-a-and-vi-a-

  5. MSP430I2040: External source resistance value of SD24 of MSP430i2040 - MSP low-power microcontroller forum - MSP low-power microcontrollers - TI E2E support forums. (2018, December 6). Ti.com. . Retrieved May 31, 2022, from https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/753113/msp430i2040-external-source-resistance-value-of-sd24-of-msp430i2040
  6. MSP430I2040: About SD24 input of i2040 - MSP low-power microcontroller forum - MSP low-power microcontrollers - TI E2E support forums. (2019). E2e.ti.com. Retrieved May 31, 2022, from https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/752142/msp430i2040-about-sd24-input-of-i2040
  7. MSP430I2041: SD24 input characteristics? See section 29.2.6.3 of 'F5xx and 'F6xx Family Users Guide - MSP low-power microcontroller forum - MSP low-power microcontrollers - TI E2E support forums. (2019). E2e.ti.com. Retrieved May 31, 2022, from https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/776758/msp430i2041-sd24-input-characteristics-see-section-29-2-6-3-of-f5xx-and-f6xx-family-users-guide
  8. MSP430I2040: SD24 input range - MSP low-power microcontroller forum - MSP low-power microcontrollers - TI E2E support forums. (2017). E2e.ti.com. Retrieved May 31, 2022, from https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/565409/msp430i2040-sd24-input-range
  9. MSP430I2020: MSP430Fi2020 SD24, Input Range - MSP low-power microcontroller forum - MSP low-power microcontrollers - TI E2E support forums. (2018). E2e.ti.com. Retrieved May 31, 2022, from https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/681024/msp430i2020-msp430fi2020-sd24-input-range
  10. What’s The Difference Between Continuous-Time And Discrete-Time Delta-Sigma ADCs?. (May 28, 2014). www.electronicdesign.com. Retrieved May 31, 2022, from https://www.electronicdesign.com/technologies/analog/article/21799834/whats-the-difference-between-continuoustime-and-discretetime-deltasigma-adcs

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