Philips LPC214 Series User Manual page 286

Philips Semiconductors
Volume 1
Table 280
capacitance of the crystal and is usually specified by the crystal manufacturer. The actual
C
different load capacitance, the circuit will oscillate at a slightly different frequency
(depending on the quality of the crystal) compared to the specified one. Therefore for an
accurate time reference it is advised to use the load capacitors as specified in
that belong to a specific C
this table are calculated from the internal parasitic capacitances and the C
from PCB and package are not taken into account.
Table 280: Recommended values for the RTC external 32 kHz oscillator C
Crystal load capacitance
C
11 pF
13 pF
15 pF
User manual
Fig 63. RTC 32kHz crystal oscillator circuit
gives the crystal parameters that should be used. C
influences oscillation frequency. When using a crystal that is manufactured for a
L
L
Rev. 01 — 15 August 2005
LPC2141/2/4/6/8
RTXC1
32 kHz Xtal
C
X1
. The value of external capacitances C
L
Maximum crystal series
resistance R
S
< 100 kΩ
< 100 kΩ
< 100 kΩ
UM10139
Chapter 19: RTC
RTXC2
C
X2
is the typical load
L
and C
X1
X1/X2
External load capacitors C
18 pF, 18 pF
22 pF, 22 pF
27 pF, 27 pF
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Table 280
specified in
X2
. Parasitics
L
components
,
X1 CX2
286