LPC2138FBD64 NXP Semiconductors, LPC2138FBD64 Datasheet - Page 38

• Manufacturer Part Number: LPC2138FBD64
• Description: 16/32BIT MCU ARM7, 512K FLASH, 64LQFP
• Manufacturer: NXP Semiconductors

Specifications of LPC2138FBD64

• No. Of I/o's: 47
• Ram Memory Size: 32KB
• Cpu Speed: 60MHz
• No. Of Timers: 2
• No. Of Pwm Channels: 6
• Digital Ic Case: RoHS Compliant
• Core Size: 32bit
• Program Memory Size: 512KB
• Oscillator Type: External Only
• Controller Family/series: LPC21xx
• Rohs Compliant: Yes

NXP Semiconductors
LPC2131_32_34_36_38
Product data sheet
12.2 RTC 32 kHz oscillator component selection
12.3 XTAL and RTCX Printed Circuit Board (PCB) layout guidelines
The RTC external oscillator circuit is shown in
integrated on chip, only a crystal, the capacitances C
externally to the microcontroller.
Table 12
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 12.
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
third overtone crystal usage have a common ground plane. The external components
must also be connected to the ground plain. 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
accordingly to the increase in parasitics of the PCB layout.
Crystal load capacitance
C
11 pF
13 pF
15 pF
Fig 15. 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 the RTC external 32 kHz oscillator C
All information provided in this document is subject to legal disclaimers.
RTCX1
C X1
LPC2xxx
32 kHz XTAL
Rev. 5 — 2 February 2011
L
Maximum crystal series
resistance R
< 100 kΩ
< 100 kΩ
< 100 kΩ
. The value of external capacitances C
RTCX2
C X2
X1
/C
X2
S
evaluation
x1
LPC2131/32/34/36/38
Figure
and C
Single-chip 16/32-bit microcontrollers
X1
=
15. Since the feedback resistance is
x2
External load capacitors C
18 pF, 18 pF
22 pF, 22 pF
27 pF, 27 pF
and C
should be chosen smaller
L
X2
is the typical load
x1
need to be connected
, C
L
C L
R S
X1
x2
and C
002aaf495
, and C
© NXP B.V. 2011. All rights reserved.
X1
C P
/C
L
X2
. Parasitics
X2
specified in
x3
components
Table 12
in case of
X1
/C
38 of 45
X2