SLAA423A December   2009  – November 2018 MSP430F4132 , MSP430F4152 , MSP430F47126 , MSP430F47127 , MSP430F47163 , MSP430F47166 , MSP430F47167 , MSP430F47173 , MSP430F47176 , MSP430F47177 , MSP430F47183 , MSP430F47186 , MSP430F47187 , MSP430F47193 , MSP430F47196 , MSP430FG4616 , MSP430FG4617 , MSP430FG4618

 

  1.   XOSC8 Guidance
    1.     Trademarks
    2. 1 Introduction
    3. 2 Contribution of ESR, Load Capacitance, VCC, and Temperature
      1. 2.1 Crystal ESR
        1. 2.1.1 ESR and Start-up Reliability
        2. 2.1.2 ESR Specification
      2. 2.2 Load Capacitance
      3. 2.3 Temperature and VCC
    4. 3 Using a Shunt Resistor From XIN to GND
    5. 4 Failsafe Mechanisms
      1. 4.1 2xx Family
      2. 4.2 4xx Family
    6. 5 Summary
    7. 6 References
  2.   Revision History

2.1.2 ESR Specification

Most crystal data sheets specify a typical and maximum ESR value for the crystal. For those vendors that do not provide a typical value, a good rule of thumb is 15 kΩ below the maximum. For example, if the vendor specifies a 50-kΩ maximum, the typical ESR is probably approximately 35 kΩ, while a 60-kΩ maximum ESR crystal is typically approximately 45 kΩ and is above the erratum requirement.

Taking the 50-kΩ (maximum) ESR crystal in the pervious example and adding 10 to 15 kΩ of series resistance does not address the XOSC8 erratum. ESR is a function of the mechanical losses due to vibration (RM), parasitic capacitance of the package (C0), and the required load capacitance (CL) (see equation 1 in MSP430 32-kHz Crystal Oscillators). In some cases, applying as much as 90 kΩ or greater series resistance was required to prevent the XOSC8 failure with a 14-kΩ ESR crystal (crystal 1b) instead of simply adding 26 kΩ to reach the 40-kΩ requirement. The impacts of adding such a large series resistance are a decreased safety factor and an increased start-up time.