Specifications

© NXP Laboratories UK 2013 JN-DS-JN5148-001 1v9 93
Three examples of typical crystals are given, each with the value of external capacitors to use, plus the likely supply
current and start-up time that can be expected. Also given is the maximum recommended ESR based on the start-up
criteria given in Appendix B.1.3. The values of the external capacitors can be calculated using the equation in
Appendix B.1.2 .
Load Capacitance Ext Capacitors Current Start-up Time Max ESR
9pF 15pF 1.6uA 0.8Sec
70KΩ
6pF 9pF 1.4uA 0.6sec
80KΩ
12.5pF 22pF 2.4uA 1.1sec
35KΩ
Below is measurement data showing the variation of the crystal oscillator supply current with voltage and with crystal
ESR, for two load capacitances.
32KHz Crystal Oscillator Current
0.6
0.8
1
1.2
1.4
1.6
2.2 2.4 2.6 2.8 3 3.2 3.4 3.6
Supply Voltage (VDD)
Normalised Current (IDD)
32KHz Crystal Oscillator Current
0.6
0.8
1
1.2
1.4
1.6
10 20 30 40 50 60 70 80
Crystal ESR (K ohm)
Normalised Current (IDD)
9pF
12.5pF