SLAA148A October   2002  – October 2018 MSP430BT5190 , MSP430F1101 , MSP430F1101A , MSP430F1111A , MSP430F112 , MSP430F1121 , MSP430F1121A , MSP430F1122 , MSP430F1132 , MSP430F122 , MSP430F1222 , MSP430F123 , MSP430F1232 , MSP430F133 , MSP430F135 , MSP430F147 , MSP430F1471 , MSP430F148 , MSP430F1481 , MSP430F149 , MSP430F1491 , MSP430F155 , MSP430F156 , MSP430F157 , MSP430F1610 , MSP430F1611 , MSP430F1612 , MSP430F167 , MSP430F168 , MSP430F169 , MSP430F2001 , MSP430F2002 , MSP430F2003 , MSP430F2011 , MSP430F2012 , MSP430F2013 , MSP430F2013-EP , MSP430F2101 , MSP430F2111 , MSP430F2112 , MSP430F2121 , MSP430F2122 , MSP430F2131 , MSP430F2132 , MSP430F2232 , MSP430F2234 , MSP430F2252 , MSP430F2252-Q1 , MSP430F2254 , MSP430F2272 , MSP430F2272-Q1 , MSP430F233 , MSP430F2330 , MSP430F235 , MSP430F2350 , MSP430F2370 , MSP430F2410 , MSP430F2416 , MSP430F2417 , MSP430F2418 , MSP430F2419 , MSP430F247 , MSP430F2471 , MSP430F248 , MSP430F2481 , MSP430F249 , MSP430F2491 , MSP430F2616 , MSP430F2617 , MSP430F2618 , MSP430F2619 , MSP430F412 , MSP430F413 , MSP430F4132 , MSP430F415 , MSP430F4152 , MSP430F417 , MSP430F423 , MSP430F423A , MSP430F425 , MSP430F4250 , MSP430F425A , MSP430F4260 , MSP430F427 , MSP430F4270 , MSP430F427A , MSP430F435 , MSP430F4351 , MSP430F436 , MSP430F4361 , MSP430F437 , MSP430F4371 , MSP430F438 , MSP430F439 , MSP430F447 , MSP430F448 , MSP430F4481 , MSP430F449 , MSP430F4491 , MSP430F4616 , MSP430F46161 , MSP430F4617 , MSP430F46171 , MSP430F4618 , MSP430F46181 , MSP430F4619 , MSP430F46191 , MSP430F47126 , MSP430F47127 , MSP430F47163 , MSP430F47166 , MSP430F47167 , MSP430F47173 , MSP430F47176 , MSP430F47177 , MSP430F47183 , MSP430F47186 , MSP430F47187 , MSP430F47193 , MSP430F47196 , MSP430F47197 , MSP430F477 , MSP430F478 , MSP430F4783 , MSP430F4784 , MSP430F479 , MSP430F4793 , MSP430F4794 , MSP430F5232 , MSP430F5234 , MSP430F5237 , MSP430F5239 , MSP430F5242 , MSP430F5244 , MSP430F5247 , MSP430F5249 , MSP430F5252 , MSP430F5253 , MSP430F5254 , MSP430F5255 , MSP430F5256 , MSP430F5257 , MSP430F5258 , MSP430F5259 , MSP430F5304 , MSP430F5308 , MSP430F5309 , MSP430F5310 , MSP430F5324 , MSP430F5325 , MSP430F5326 , MSP430F5327 , MSP430F5328 , MSP430F5329 , MSP430F5333 , MSP430F5336 , MSP430F5338 , MSP430F5340 , MSP430F5341 , MSP430F5342 , MSP430F5418 , MSP430F5418A , MSP430F5419 , MSP430F5419A , MSP430F5435 , MSP430F5435A , MSP430F5436 , MSP430F5436A , MSP430F5437 , MSP430F5437A , MSP430F5438 , MSP430F5500 , MSP430F5501 , MSP430F5502 , MSP430F5503 , MSP430F5504 , MSP430F5505 , MSP430F5506 , MSP430F5507 , MSP430F5508 , MSP430F5509 , MSP430F5510 , MSP430F5630 , MSP430F5631 , MSP430F5632 , MSP430F5633 , MSP430F5634 , MSP430F5635 , MSP430F5636 , MSP430F5637 , MSP430F5638 , MSP430F6433 , MSP430F6435 , MSP430F6436 , MSP430F6438 , MSP430F6630 , MSP430F6631 , MSP430F6632 , MSP430F6633 , MSP430F6634 , MSP430F6635 , MSP430F6636 , MSP430F6637 , MSP430F6638 , MSP430FE423 , MSP430FE4232 , MSP430FE423A , MSP430FE4242 , MSP430FE425 , MSP430FE4252 , MSP430FE425A , MSP430FE427 , MSP430FE4272 , MSP430FE427A , MSP430FG4250 , MSP430FG4260 , MSP430FG4270 , MSP430FG4616 , MSP430FG4617 , MSP430FG4618 , MSP430FG4619 , MSP430FG477 , MSP430FG478 , MSP430FG479 , MSP430FW423 , MSP430FW425 , MSP430FW427 , MSP430FW428 , MSP430FW429 , MSP430G2001 , MSP430G2101 , MSP430G2102 , MSP430G2111 , MSP430G2112 , MSP430G2121 , MSP430G2131 , MSP430G2132 , MSP430G2152 , MSP430G2201 , MSP430G2201-Q1 , MSP430G2211 , MSP430G2212 , MSP430G2221 , MSP430G2231-Q1 , MSP430G2232 , MSP430G2252 , MSP430G2302 , MSP430G2312 , MSP430G2332 , MSP430G2352 , MSP430G2402 , MSP430G2432 , MSP430G2452 , MSP430L092

 

  1.   Interfacing the 3-V MSP430™ MCUs to 5-V Circuits
    1.     Trademarks
    2. 1 Introduction
    3. 2 Definitions
      1. 2.1 Specification Values of MSP430 MCU
      2. 2.2 External System Definitions
    4. 3 Input Interfaces
      1. 3.1 Resistor-Divider Input Interfaces
      2. 3.2 Transistor Input Interface
      3. 3.3 Op-Amp Input Interface
      4. 3.4 TPL7407LA Input Interface
      5. 3.5 Integrated-Circuit Input Interface
      6. 3.6 Analog Input Interface
    5. 4 Output Interfaces
      1. 4.1 Transistor Output Interface
      2. 4.2 Interface to CMOS-TTL Inputs
      3. 4.3 Interface to TPL7407LA Inputs
      4. 4.4 Op-Amp Output Interface
      5. 4.5 Integrated-Circuit Output Interface
    6. 5 Bidirectional Interfaces
      1. 5.1 Simple Bidirectional Op-Amp Interface
      2. 5.2 Integrated-Circuit I/O Interface
    7. 6 Power Supplies
    8. 7 Summary
    9. 8 References
  2.   Revision History

3.1 Resistor-Divider Input Interfaces

An external digital input voltage (VI(sys)) is connected to the MSP430 MCU. The worst case equations for the resistors R1 and R2 in Figure 2 are:

Equation 2. R1 R2 < V ( sysH ) min - V IT ( max ) V IT ( max ) × (1 +2 p ) R1 R2 > V ( sysL ) max - V IT ( min ) V IT ( min ) × (1 -2 p ) R1 ∥ R2 ≪ DV CC |   I lkg   |

The first two equations ensure that the input voltage VI(430) at the input of the MSP430 MCU is above (when VI(sys) is high) or below (when VI(sys) is low) the worst case input threshold voltages. The third equation ensures that the leakage current Ilkg of the input does not influence the voltage VI(430).

To avoid current into the input protection diodes of the MSP430 MCU, Equation 3 must be true.

Equation 3. V sysH ( max ) × R2 max R1 min + R2 max < DV CC ( min ) +0 .3 V sysL ( min ) × R2 min R1 max + R2 min > –0 .3
resistor-input-interface-from-5-v-to-the-msp430-mcu.gifFigure 2. Resistor Input Interface From 5 V to the MSP430

Example: The two input voltages from the system are V(sysH) = 5.0 V ±10% and V(sysL) = 0.5 V ±0.5 V. The resistor tolerance is p = ±5%. The minimum supply voltage of the MSP430 MCU in this example is DVCC(min) = 2.7 V (3.0 V – 10%).

The specifications for the threshold voltages VIT(max) and VIT(min) lead to the following condition for the input voltage V(sysH)min:

Equation 4. R1 R2 < V ( sysH ) min - V IT ( max ) V IT ( max ) × (1 +2 p ) = 4 .5 V -1 .9 V 1 .9 V × (1 +0 .1 )   →   R1 R2 <1 .244

The condition for the low input voltage V(sysL)max is:

Equation 5. R1 R2 > V ( sysL ) max - V IT ( min ) V IT ( min ) × (1 -2 p ) = 1 .0 V -0 .9 V 0 .9 V × (1 -0 .1 )   →   R1 R2 >0 .1234

To ensure negligible influence of the leakage current Ilkg:

Equation 6. R1 ∥ R2 ≪ DV CC | I lkg | = 3 V | ±50 nA |   →   R1 ∥ R2 ≪60 MΩ

The previous three design equations allow a wide range for R1 and R2. If R1/R2 is chosen to be 1.0 and R1||R2 is chosen to be 600 kΩ, then R1 = 1.2 MΩ and R2 = 1.2 MΩ.

To avoid current into the input protection diodes of the MSP430 MCU:

Equation 7. V ( sysH ) max × R2 max R1 min + R2 max < DV CC ( min ) +0 .3 V ( sysL ) min × R2 min R1 max + R2 min > -0 .35 .5 V × 1 .26 MΩ 1 .14 MΩ +1 .26 MΩ <2 .7 V +0 .3   →  2 .8875 V <3 .0 V     →   the condition is true0 .0 V × 1 .14 MΩ 1 .26 MΩ +1 .14 MΩ > -0 .3   →0 .0 V > -0 .3     →    the condition is also true

The last two equations are not important if the current into the input of the MSP430 MCU is far below ±2 mA (the absolute maximum rating value for an input current). This is the case for R1||R2 = 600 kΩ.

The design equations are valid for the following terminals of the MSP430 MCU, if set to the input direction:

  • All I/O ports (ports P1 to P6)
  • Crystal inputs XIN and XT2IN: VIL(X)max = 0.2 × DVCC, VIH(X)min = 0.8 × DVCC
  • RST/NMI input: VILmax = DVSS +0.6 V, VIHmin = 0.8 × DVCC
  • Comparator_A inputs CA0 and CA1
  • UART and SPI inputs URXDx, SOMIx, SIMOx, UCLK
  • Timer_A inputs TACLK and TA0 to TA2
  • Timer_B inputs TBCLK and TB0 to TB6
  • ADC12 inputs: the sample time t(sample) must be adapted to the impedance R1||R2 of the resistor divider. For more information, see the ADC12 chapter of the MSP430x4xx Family User’s Guide or the MSP430x1xx Family User’s Guide.