Datasheet
Table Of Contents
- 1. General description
- 2. Features and benefits
- 3. Applications
- 4. Ordering information
- 5. Block diagram
- 6. Pinning information
- 7. Functional description
- 7.1 Architectural overview
- 7.2 On-chip flash programming memory
- 7.3 On-chip SRAM
- 7.4 Memory map
- 7.5 Interrupt controller
- 7.6 Pin connect block
- 7.7 General purpose DMA controller
- 7.8 Fast general purpose parallel I/O
- 7.9 Ethernet (LPC2362 only)
- 7.10 USB interface
- 7.11 CAN controller and acceptance filters
- 7.12 10-bit ADC
- 7.13 10-bit DAC
- 7.14 UARTs
- 7.15 SPI serial I/O controller
- 7.16 SSP serial I/O controller
- 7.17 I2C-bus serial I/O controllers
- 7.18 I2S-bus serial I/O controllers
- 7.19 General purpose 32-bit timers/external event counters
- 7.20 Pulse width modulator
- 7.21 Watchdog timer
- 7.22 RTC and battery RAM
- 7.23 Clocking and power control
- 7.24 System control
- 7.25 Emulation and debugging
- 8. Limiting values
- 9. Thermal characteristics
- 10. Static characteristics
- 11. Dynamic characteristics
- 12. ADC electrical characteristics
- 13. DAC electrical characteristics
- 14. Application information
- 15. Package outline
- 16. Abbreviations
- 17. Revision history
- 18. Legal information
- 19. Contact information
- 20. Contents
LPC2361_62 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 5.1 — 15 October 2013 54 of 65
NXP Semiconductors
LPC2361/62
Single-chip 16-bit/32-bit MCU
14.3 RTC 32 kHz oscillator component selection
The RTC external oscillator circuit is shown in Figure 24. Since the feedback resistance is
integrated on chip, only a crystal, the capacitances C
X1
and C
X2
need to be connected
externally to the microcontroller.
Table 17
gives the crystal parameters that should be used. C
L
is the typical load
capacitance of the crystal and is usually specified by the crystal manufacturer. The actual
C
L
influences oscillation frequency. When using a crystal that is manufactured for a
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 Table 17
that belong to a specific C
L
. The value of external capacitances C
X1
and C
X2
specified in
this table are calculated from the internal parasitic capacitances and the C
L
. Parasitics
from PCB and package are not taken into account.
14.4 XTAL and RTCX Printed Circuit Board (PCB) layout guidelines
The crystal should be connected on the PCB as close as possible to the oscillator input
and output pins of the chip. Take care that the load capacitors C
x1
, C
x2
, and C
x3
in case of
third overtone crystal usage have a common ground plane. The external components
must also be connected to the ground plane. Loops must be made as small as possible in
order to keep the noise coupled in via the PCB as small as possible. Also parasitics
should stay as small as possible. Values of C
x1
and C
x2
should be chosen smaller
accordingly to the increase in parasitics of the PCB layout.
Fig 24. RTC oscillator modes and models: oscillation mode of operation and external
crystal model used for C
X1
/C
X2
evaluation
Table 17. Recommended values for the RTC external 32 kHz oscillator C
X1
/C
X2
components
Crystal load capacitance
C
L
Maximum crystal series
resistance R
S
External load capacitors C
X1
/C
X2
11 pF < 100 k 18 pF, 18 pF
13 pF < 100 k 22 pF, 22 pF
15 pF < 100 k 27 pF, 27 pF
002aaf495
LPC2xxx
RTCX1 RTCX2
C
X2
C
X1
32 kHz XTAL
=
C
L
C
P
R
S
L