Nxp Semiconductors PCA2125 User Manual

 

 

UM10301_1 

© NXP B.V. 2008. All rights reserved.

Taking the numbers from Table 4 yields for L

1

 and Q: 

 

 

(

)

(

)

11234

10

1

.

2

32768

2

1

2

1

15

2

1

2

0

1

=

⋅

⋅

⋅

=

⋅

⋅

=

−

π

π

 

 

 

(

)

(

)

42053

10

55

10

1

.

2

32768

2

1

2

1

3

15

1

1

0

=

⋅

⋅

⋅

⋅

⋅

=

⋅

⋅

⋅

=

−

π

π

 

 

This L of around 11000 H resulting in a Q of around 42000 explains why starting up the 
oscillator as well as stopping it can easily take more than a second. An oscillating quartz 
crystal is actually a mechanical oscillation and starting or stopping this takes time. 
Calculations of start up time and more in-depth theory about the oscillator and load 
capacitance are beyond the scope of this user manual, but can be found in AN10716 
“Background information and theory related to Real Time Clocks and crystals”. 

The use of AGC’s improve start up by high drive initially to get it going and then reduce 
drive for low power. 

f

0 

32768 Hz 

[2] 

∆f / f

0

 ±100  ppm  [2] 

Aging; ∆f / f

0 

±3…±5 ppm 

[2] 

B, freq(T) 

-0.035 

ppm / °C

2

 [2] 

C

1

 2.1 fF  [2] 

C

0

 1.2…1.5 

pF [2] 

C

IN

 

25 ± 10 

pF 

[1] 

C

IN

, temp co. 

+47  

ppm/°C 

[1] 

R

1

 50…80 

kΩ [2] 

C

T

 variable 

4…25 

pF 

[3] 

C

T

, temp co. 

300  

ppm/°C  

[3] 

C

T

 fixed 0603 

Any 

pF 

[4] 

C

T

 fixed, tc 

±30 for C0G 

ppm/°C 

[4] 

Sources for values in table 4: 

[1]  NXP, Datasheet PCF8563, February 2008. 

[2]  Product Data Sheets, MicroCrystal. 

[3]  Murata TZB04 trim capacitor 

[4]   Vishay Beyschlag, datasheet ceramic multilayer capacitor, C0G