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

5.1 Simple Bidirectional Op-Amp Interface

If true I/O performance is needed between the MSP430 MCU and a 5-V system, then the interface circuit in Figure 9 can be used. The op amp works as a flip-flop: the I/O pin currently working as an output controls the state of this flip-flop. The other I/O pin must be an input.

bidirectional-interface-between-3-v-and-5-v-systems.gifFigure 9. Bidirectional Interface Between 3-V and 5-V Systems

The worst-case design equations for the resistors R3, R,4 and R5 follow. Equation 21 ensures a high level at the MSP430 input.

Equation 21. R4 R5 < (1 -2 p ) × V ( sysH ) min V ref ( max ) -1

Equation 22 prevents voltages higher than DVCC at the MSP430 input.

Equation 22. R4 R5 > (1 +2 p ) × V ( sysH ) max DV CC ( min ) -1

Equation 23 ensures high level at the input of the MSP430 MCU with the MSP430 and op amp leakage currents Ilkg and Ilkg(Op).

Equation 23. R4 < V ( sysH ) min - V ref ( max ) × 1 + R4 R5 × (1 +2 p ) I lkg + I lkg ( Op ) × (1 + p )

Equation 24 ensures a high level at the external system input with its leakage current Ilkg(sys).

Equation 24. R3 < V ( sys ) min - V ( sys + ) min (1 + p ) × I lkg ( sys ) + V ( sys + ) min - V ref ( min ) R4 × (1 + p )
  • Vref = Reference voltage for the input level decision (V)
  • Ilkg = Input leakage current of an MSP430 input (A)
  • Ilkg(Op) = Input leakage current of the opamp input (A)
  • Ilkg(sys) = Input leakage current of the system input (A)

Example: Bidirectional interface for the following data: V(sys) = 5 V ±10%, V(sysH)min = 4 V, V(sys+)max = 3.5 V, Ilkg(sys) = ±1 µA, Ilkg(Op) = ±700 pA, Ilkg = ±50 nA, Vref = 1.5 V ±5%. The resistor tolerance is p = ±5%. The minimum supply voltage of this example is DVCC(min) = 2.7 V (3.0 V – 10%).

Equation 25. R4 R5 < (1 -2 p ) × V ( sysH ) min V ref ( max ) -1 = (1 -2 ×0 .05 ) × 4 V 1 .575 V -1 =1 .386
Equation 26. R4 R5 > (1 +2 p ) × V ( sysH ) max DV CC ( min ) -1 = (1 +2 ×0 .05 ) × 5 .5 V 2 .7 V -1 =1 .14

The median value of the R4 and R5 limits is Equation 27.

Equation 27. R4 R5   =   1 .38   +  1 .14 2   =  1 .26
Equation 28. R4 < V ( sysH ) min - V ref ( max ) × 1 + R4 R5 × (1 +2 p ) I lkg + I lkg ( Op ) × (1 + p ) = 4 .0 V -1 .575 V × 1 +1 .26 × (1 +2 ×0 .05 ) 50 nA +700 pA × (1 +0 .05 ) =4 .55 MΩ

R4 is chosen to be 2 MΩ.

Resistor R5 is calculated as Equation 29.

Equation 29. R5 = R4 1 .26 = 2 MΩ 1 .26 =1 .59 MΩ
Equation 30. R3 < V ( sys ) min - V ( sys + ) min (1 + p ) × I lkg ( sys ) + V ( sys + ) min - V ref ( min ) R4 × (1 + p ) = 4 .5 V -3 .5 V (1 +0 .05 ) × 1 µ A + 3 .5 V -1 .425 V 2 MΩ × (1 +0 .05 ) =479 kΩ

The three chosen resistors are: R3 = 330 kΩ, R4 = 2 MΩ, R5 = 1.6 MΩ