Datasheet

LPC15XX All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
Product data sheet Rev. 1 — 19 February 2014 88 of 99
NXP Semiconductors
LPC15xx
32-bit ARM Cortex-M3 microcontroller
14.4 RTC oscillator component selection
The 32 kHz crystal must be connected to the part via the RTCXIN and RTCXOUT pins as
shown in Figure 48
. If the RTC is not used, the RTCXIN pin can be grounded.
Select C
x1
and C
x2
based on the external 32 kHz crystal used in the application
circuitry.The pad capacitance C
P
of the RTCXIN and RTCXOUT pad is 3 pF. If the external
crystal’s load capacitance is C
L
, the optimal C
x1
and C
x2
can be selected as:
C
x1
= C
x2
= 2 x C
L
– C
P
Fig 48. RTC oscillator components
LPC1xxx
RTCXIN RTCXOUT
C
X2
C
X1
XTAL
=
C
L
C
P
R
S
L
aaa-010822