SLAA322D August   2006  – July 2017 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 , MSP430F2274 , 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 , MSP430F5438A , MSP430F5500 , MSP430F5501 , MSP430F5502 , MSP430F5503 , MSP430F5504 , MSP430F5505 , MSP430F5506 , MSP430F5507 , MSP430F5508 , MSP430F5509 , MSP430F5510 , MSP430F5513 , MSP430F5514 , MSP430F5515 , MSP430F5517 , MSP430F5519 , MSP430F5521 , MSP430F5522 , MSP430F5524 , MSP430F5525 , MSP430F5526 , MSP430F5527 , MSP430F5528 , MSP430F5529 , MSP430F5630 , MSP430F5631 , MSP430F5632 , MSP430F5633 , MSP430F5634 , MSP430F5635 , MSP430F5636 , MSP430F5637 , MSP430F5638 , MSP430F6433 , MSP430F6435 , MSP430F6436 , MSP430F6438 , MSP430F6630 , MSP430F6631 , MSP430F6632 , MSP430F6633 , MSP430F6634 , MSP430F6635 , MSP430F6636 , MSP430F6637 , MSP430F6638 , MSP430F6720 , MSP430F6720A , MSP430F6721 , MSP430F6721A , MSP430F6723 , MSP430F6723A , MSP430F6724 , MSP430F6724A , MSP430F6725 , MSP430F6725A , MSP430F6726 , MSP430F6726A , MSP430F6730 , MSP430F6730A , MSP430F6731 , MSP430F6731A , MSP430F6733 , MSP430F6733A , MSP430F6734 , MSP430F6734A , MSP430F6735 , MSP430F6735A , MSP430F6736 , MSP430F6736A , MSP430F6745 , MSP430F67451 , MSP430F67451A , MSP430F6745A , MSP430F6746 , MSP430F67461 , MSP430F67461A , MSP430F6746A , MSP430F6747 , MSP430F67471 , MSP430F67471A , MSP430F6747A , MSP430F6748 , MSP430F67481 , MSP430F67481A , MSP430F6748A , MSP430F6749 , MSP430F67491 , MSP430F67491A , MSP430F6749A , MSP430F6765 , MSP430F67651 , MSP430F67651A , MSP430F6765A , MSP430F6766 , MSP430F67661 , MSP430F67661A , MSP430F6766A , MSP430F6767 , MSP430F67671 , MSP430F67671A , MSP430F6767A , MSP430F6768 , MSP430F67681 , MSP430F67681A , MSP430F6768A , MSP430F6769 , MSP430F67691 , MSP430F67691A , MSP430F6769A , MSP430F6775 , MSP430F67751 , MSP430F67751A , MSP430F6775A , MSP430F67761 , MSP430F67761A , MSP430F6776A , MSP430F67771 , MSP430F67771A , MSP430F6777A , MSP430F67781 , MSP430F67781A , MSP430F6778A , MSP430F67791 , MSP430F67791A , MSP430F6779A , MSP430FE423 , MSP430FE4232 , MSP430FE423A , MSP430FE4242 , MSP430FE425 , MSP430FE4252 , MSP430FE425A , MSP430FE427 , MSP430FE4272 , MSP430FE427A , MSP430FG4250 , MSP430FG4260 , MSP430FG4270 , MSP430FG437 , MSP430FG438 , MSP430FG439 , MSP430FG4616 , MSP430FG4617 , MSP430FG4618 , MSP430FG4619 , MSP430FG477 , MSP430FG478 , MSP430FG479 , MSP430FW423 , MSP430FW425 , MSP430FW427 , MSP430G2001 , MSP430G2101 , MSP430G2102 , MSP430G2111 , MSP430G2112 , MSP430G2121 , MSP430G2131 , MSP430G2132 , MSP430G2152 , MSP430G2201 , MSP430G2201-Q1 , MSP430G2211 , MSP430G2212 , MSP430G2221 , MSP430G2231 , MSP430G2231-Q1 , MSP430G2232 , MSP430G2252 , MSP430G2302 , MSP430G2312 , MSP430G2332 , MSP430G2352 , MSP430G2402 , MSP430G2432 , MSP430G2452 , MSP430L092

 

  1.   MSP430rep%#8482; 32-kHz Crystal Oscillators
    1.     Trademarks
    2. 1 The 32-kHz Crystal Oscillator
      1. 1.1 The Crystal
      2. 1.2 The Oscillator
    3. 2 Crystal Selection
      1. 2.1 Effective Load Capacitance
      2. 2.2 ESR Value
      3. 2.3 Tolerance
      4. 2.4 Start-up Time
    4. 3 PCB Design Considerations
    5. 4 Testing the Crystal Oscillator
      1. 4.1 Oscillator Frequency vs Load Capacitance
      2. 4.2 Negative Resistance Method
      3. 4.3 Relationship Between Crystal ESR and Safety Factor
    6. 5 Crystal Oscillator in Production
      1. 5.1 PCB Material, Quality, and Cleaning
      2. 5.2 Soldering and Contact Impedance
      3. 5.3 Environmental Influences, Temperature, and Humidity
      4. 5.4 Device-Specific Features to Support Better Start-up Behavior
    7. 6 Hardware Troubleshoot for Crystal-Oscillator Start-up in Production
    8. 7 References
  2.   Revision History

4.3 Relationship Between Crystal ESR and Safety Factor

To further show the importance of ESR on a crystal's ability to oscillate properly, the negative resistance method detailed in Section 4.2 was used on a selection of crystal oscillators with varying packages, ESR values, and tolerances. The test was performed using a MSP430FE427A device populated on a MSP-TS430PM64 target board, a platform whose design does not follow the recommendations detailed by this application report. The RQmax value of each crystal was determined by placing a potentiometer in series followed by testing for the crystal's start and stop allowances. The nearest standard resistor value (±5%) was recorded as general reference. The exact oscillation allowances and safety factors were also calculated using Equation 4 and Equation 5. Table 3 outlines the outcome of these tests. Note that results will differ based on variables such as PCB design, board cleanliness or amount of flux present, and quantity of solder used, all of which affect the system's parasitic capacitance. The size and dimensions of all crystals used in this example are similar, but accommodations were made to establish connections to the target board and the various package types.

Table 3. Safety Factor Test Results

Mouser Crystal Part Number Package ESR
(kΩ)		 Tolerance
(±ppm)		 RQmax
(kΩ)		 Standard Value
(kΩ)		 OA
(kΩ)		 SF(1)
AB26T-32.768KHZ Radial 35 20 257 240 292 8.34
CFS206-32.768KEZB-U Radial 35 10 254 240 289 8.26
AB26TRQ-32.768kHz-T Radial 50 20 195 180 245 4.90
MC-306 32.7680K-A0 4-SOJ 35 20 233 220 268 7.66
ABS25-32.768KHZ-T 4-SOJ 50 20 250 240 300 6.00
CM200C-32.768KDZB-UT 4-SOJ 50 20 242 240 292 5.84
ABS25-32.768KHz-6-1-T 4-SOJ 50 10 238 220 288 5.76
FC-12M 32.7680KA-A3 2-SMD 90 20 178 160 268 2.98
ABS10-32.768KHZ-T 2-SMD 70 20 213 200 283 4.04
ABS07-32.768KHZ-1-T 2-SMD 70 10 197 180 267 3.81
FC-135R 32.7680KA 2-SMD 50 20 246 240 296 5.92
(1) While some tests resulted in safety factors in the suitable and safe categories, the target boards are not ideal test fixtures due to the socket.

As Table 3 shows, crystals with a lower ESR produce a higher RQmax, which proportionately results in higher oscillation allowances and safety factors.