Crystal Oscillator - Philips LPC2119 User Manual

Philips Semiconductors
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
processor clock frequency is referred to as cclk for purposes of rate equations, etc. elsewhere in this document. F
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
case of fundamental mode oscillation (the fundamental frequency is represented by L, C
drawing c, represents the parallel package capacitance and should not be larger than 7 pF. Parameters F
supplied by the crystal manufacturer.
LPC2119/2129
LPC2292/2294
X1
C
C
Clock
a)
Figure 12: Oscillator modes and models: a) slave mode of operation, b) oscillation mode of operation,
Table 13: Recommended values for C
Fundamental Oscillation
Frequency F
10 - 15 MHz
15 - 20 MHz
20 - 25 MHz
System Control Block
LPC2119/2129
LPC2292/2294
X2 X1
C
X1
c) external crystal model used for C
when oscillation mode is used
X1/X2
Crystal Load
Capacitance C
C
10 pF
20 pF
30 pF
10 pF
20 pF
30 pF
10 pF
20 pF
30 pF
and C
X1
X2
Xtal
C
X2
b)
evaluation
X1/X2
Max. Crystal Series
Resistence R
L
< 300 Ω
< 220 Ω
< 140 Ω
< 220 Ω
< 140 Ω
< 80 Ω
< 160 Ω
< 90 Ω
< 50 Ω
50
Preliminary User Manual
LPC2119/2129/2292/2294
osc
need to be connected externally in
X2
and R ). Capacitance Cp in Figure 12,
L S
, C , R
C L
L
<=>
C C
L
R
S
c)
External Load
Capacitors C
S X1
18 pF, 18 pF
38 pF, 38 pF
58 pF, 58 pF
18 pF, 18 pF
38 pF, 38 pF
58 pF, 58 pF
18 pF, 18 pF
38 pF, 38 pF
58 pF, 58 pF
January 08, 2004
and the ARM
and cclk
osc
and C are
S P
P
, C
X2