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PXA250 and PXA210 Applications Processors Design Guide 8-5
Power and Clocking
To drive the 32.768 kHz crystal pins from an external source:
• Drive the TEXTAL pin with a digital signal that has a low level near 0 V and a high level near
VCC. Do not exceed VCC or go below VSS by more than 100 mV. The minimum slew rate is
1V per
µs. The maximum current drawn by the external clock source when the clock is at its
maximum positive voltage should be about 1mA.
• Float the TXTAL pin or drive it complementary to the TEXTAL pin, using the same voltage
level, slew rate, and input current restrictions.
8.4.2 3.6864 MHz Oscillator Specifications
The 3.6864 MHz Oscillator is connected between the PXTAL (amplifier input) and PEXTAL
(amplified output). The 3.6864 MHz specifications are shown in Table 8-5
To drive the 3.6864 MHz crystal pins from an external source:
t
S_XT
Stabilization Time 2s — 10 s
Board Specifications
R
P_XT
Parasitic Resistance, TXTAL/TEXTAL to any node 20 MΩ — —
C
P_XT
Parasitic Capacitance, TXTAL/TEXTAL, total — — 5pF
C
OP_XT
Parasitic Shunt Capacitance, TXTAL to TEXTAL — — 0.4 pF
Table 8-4. 32.768 kHz Oscillator Specifications (Sheet 2 of 2)
Symbol Description Min Typical Max
Table 8-5. 3.6864 MHz Oscillator Specifications
Symbol Description Min Typical Max
Crystal Specifications - Typical is FOX HC49S
F
XP
Crystal Frequency, PXTAL/PEXTAL — 3.6864 MHz —
L
MP
Motional Inductance, PXTAL/PEXTAL — 0.50593 H —
C
MP
Motional Capacitance, PXTAL/PEXTAL — 3.68488 fF —
R
MP
Motional Resistance, PXTAL/PEXTAL 50 Ω 99.3 Ω 200 Ω
C
OP
Shunt Capacitance PXTAL to PEXTAL — 1.7 pF —
C
LP
Load Capacitance PXTAL/PEXTAL — 20 pF —
Amplifier Specifications
V
IH_X
Input High Voltage, PXTAL 0.8V*VCC — VCC
V
IL_X
Input Low Voltage, PXTAL VSS — 0.2 V*VCC
I
IN_XP
Input Leakage, PXTAL — — 10 µA
C
IN_XP
Input Capacitance, PXTAL/PEXTAL — 40 pF 50 pF
t
S_XP
Stabilization Time 17.8 ms — 67.8 ms
Board Specifications
R
P_XP
Parasitic Resistance, PXTAL/PEXTAL to any node 20 MΩ — —
C
P_XP
Parasitic Capacitance, PXTAL/PEXTAL, total — — 5pF
C
OP_XP
Parasitic Shunt Capacitance, PXTAL to PEXTAL — — 0.4 pF