pc87591l National Semiconductor Corporation, pc87591l Datasheet - Page 357

• Manufacturer Part Number: pc87591l
• Description: Lpc Mobile Embedded Controllers
• Manufacturer: National Semiconductor Corporation

Revision 1.07
Host-Controlled Modules and Host Interface
External Elements
Choose C1 and C2 capacitors (see Figure 113) to match the crystal’s load capacitance. The load capacitance C
crystal Y is comprised of C
pacitance is caused by the chip package, board layout and socket (if any), and can vary from 0 to 8 pF. The rule of thumb
for choosing these capacitors is:
Oscillator Start-Up
The oscillator starts to generate 32.768 KHz pulses to the RTC after approximately t
V
C
tolerance and temperature coefficients.
6.2.4
32.768 KHz can be applied from an external clock source, as shown in Figure 114.
Connections
Connect the clock to the 32KCLKIN pin, leaving the oscillator output, 32KX2, unconnected.
BATMIN
1
can be trimmed to achieve precisely 32.768 KHz. To achieve a high time accuracy, use crystal and capacitors with low
C
L
= (C
External Oscillator
(2.4 V) or from when V
1
* C
Crystal
Resistor R
Resistor R
Capacitor C
Capacitor C
Component
2
) / (C
1
+ C
1
2
1
2
1
2
Resonance Frequency
Type
Serial Resistance
Quality Factor, Q
Shunt Capacitance
Load Capacitance, C
Temperature Coefficient
Resistance
Resistance
Capacitance
Capacitance
) + C
in series with C
CC
Battery
PARASITIC
B1
Parameters
is higher than V
Table 65. Crystal Oscillator Circuit Components
Figure 114. External Oscillator Connections
V
BAT
CF
2
and in parallel with the parasitic capacitance of the circuit. The parasitic ca-
CF
L
OUT
POWER
CCMIN
32KCLKIN /
32KX1
32.768 KHz Parallel Mode
(3.0V).
357
N-Cut or XY-bar
User defined
Clock Generator
9-13 pF
121 K
Values
(Continued)
20 M
40 K
35000
10 pF
12 pF
32.768 KHz
2 pF
NC
32KX2
To other
modules
CF = 0.1 F
External
Internal
32KW
User defined
Tolerance
from when V
10%
10%
Max
Max
Min
5%
5%
BAT
is higher than
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