50
Philips Semiconductors
Preliminary User Manual
LPC2119/2129/2292/2294
ARM-based Microcontroller
CRYSTAL OSCILLATOR
The oscillator supports crystals in the range of 10 MHz to 25 MHz. The oscillator output frequency is called F
osc
and the ARM
processor clock frequency is referred to as cclk for purposes of rate equations, etc. elsewhere in this document. F
osc
and cclk
are the same value unless the PLL is running and connected. Refer to the PLL description in this chapter for details.
Onboard oscillator in LPC2119/2129/2292/2294 can operate in one of two modes: slave mode and oscillation mode.
In slave mode the input clock signal should be coupled by means of a capacitor of 100 pF (Cc in Figure 12, drawing a), with an
amplitude of at least 200 mVrms. X2 pin in this configuration can be left not connected.
External components and models used in oscillation mode are shown in Figure 12, drawings b and c, and in Table 13. Since the
feedback resistance is integrated on chip, only a crystal and the capacitances C
X1
and C
X2
need to be connected externally in
case of fundamental mode oscillation (the fundamental frequency is represented by L, C
L
and R
S
). Capacitance Cp in Figure 12,
drawing c, represents the parallel package capacitance and should not be larger than 7 pF. Parameters F
C
, C
L
, R
S
and C
P
are
supplied by the crystal manufacturer.
Figure 12: Oscillator modes and models: a) slave mode of operation, b) oscillation mode of operation,
c) external crystal model used for C
X1/X2
evaluation
Table 13: Recommended values for C
X1/X2
when oscillation mode is used
Fundamental Oscillation
Frequency F
C
Crystal Load
Capacitance C
L
Max. Crystal Series
Resistence R
S
External Load
Capacitors C
X1
, C
X2
10 - 15 MHz
10 pF
< 300
Ω
18 pF, 18 pF
20 pF
< 220
Ω
38 pF, 38 pF
30 pF
< 140
Ω
58 pF, 58 pF
15 - 20 MHz
10 pF
< 220
Ω
18 pF, 18 pF
20 pF
< 140
Ω
38 pF, 38 pF
30 pF
< 80
Ω
58 pF, 58 pF
20 - 25 MHz
10 pF
< 160
Ω
18 pF, 18 pF
20 pF
< 90
Ω
38 pF, 38 pF
30 pF
< 50
Ω
58 pF, 58 pF
C
L
R
S
C
P
L
<=>
X1
X2
C
X1
C
X2
Xtal
X1
X2
C
C
Clock
a)
b)
c)
LPC2119/2129
LPC2292/2294
LPC2119/2129
LPC2292/2294