LPC2470 NXP Semiconductors, LPC2470 Datasheet - Page 80

• Manufacturer Part Number: LPC2470
• Description: NXP Semiconductors designed the LPC2470 microcontroller, powered by theARM7TDMI-S core, to be a highly integrated microcontroller for a wide range ofapplications that require advanced communications and high quality graphic displays
• Manufacturer: NXP Semiconductors

NXP Semiconductors
LPC2470
Product data sheet
14.5 RTC 32 kHz oscillator component selection
Table 23.
The RTC external oscillator circuit is shown in
integrated on chip, only a crystal, the capacitances C
externally to the microcontroller.
Table 24
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 24.
Fundamental oscillation
frequency F
15 MHz to 20 MHz
20 MHz to 25 MHz
Crystal load capacitance
C
11 pF
13 pF
15 pF
Fig 31. RTC oscillator modes and models: oscillation mode of operation and external
L
L
influences oscillation frequency. When using a crystal that is manufactured for a
gives the crystal parameters that should be used. C
crystal model used for C
Recommended values for C
components parameters): high frequency mode
Recommended values for the RTC external 32 kHz oscillator C
OSC
All information provided in this document is subject to legal disclaimers.
RTCX1
C X1
LPC2xxx
32 kHz XTAL
Rev. 4 — 8 September 2011
L
Maximum crystal series
resistance R
< 100 k
< 100 k
< 100 k
Crystal load
capacitance C
10 pF
20 pF
10 pF
20 pF
. The value of external capacitances C
RTCX2
C X2
X1
/C
X2
X1
S
/C
evaluation
L
X2
in oscillation mode (crystal and external
Maximum crystal
series resistance R
< 180 
< 100 
< 160 
< 80 
Figure
Flashless 16-bit/32-bit microcontroller
X1
=
31. Since the feedback resistance is
External load capacitors C
18 pF, 18 pF
22 pF, 22 pF
27 pF, 27 pF
and C
L
X2
is the typical load
S
need to be connected
L
C L
R S
X1
and C
External load
capacitors C
18 pF, 18 pF
39 pF, 39 pF
18 pF, 18 pF
39 pF, 39 pF
002aaf495
LPC2470
© NXP B.V. 2011. All rights reserved.
X1
C P
/C
L
X2
. Parasitics
X2
specified in
components
Table 24
X1
X1
, C
/C
80 of 91
X2
X2