ADP315PC87570 National Semiconductor, ADP315PC87570 Datasheet - Page 65

• Manufacturer Part Number: ADP315PC87570
• Description: Keyboard and Power Management Controller
• Manufacturer: National Semiconductor

www.national.com
6.2.6
The internal oscillator employs an external crystal connect-
ed to the on-chip amplifier. The on-chip amplifier is accessi-
ble on the 32KX1 input pin and 32KX2 output pin. See
Figure 6-1 for the recommended external circuit, and Table
6-1 for a listing of the circuit components. The oscillator may
be disabled in certain conditions. See Section 6.2.15 on
page 68 for more details.
Figure 6-1. Recommended Oscillator External Circuitry
Table 6-1. Crystal Oscillator Circuit Components
External Elements
Choose C1 and C2 capacitors (see Figure 6-1) to match
the crystal’s load capacitance. The load capacitance C
“seen” by crystal Y is comprised of C
in parallel with the parasitic capacitance of the circuit. The
parasitic capacitance is caused by the chip package, board
layout and socket (if any), and can vary from 0 to 8 pF. The
rule of thumb in choosing these capacitors is:
Crystal
Resistor R
Resistor R
Capacitor C
Capacitor C
Component
C
0.1uF
C
L
Battery
V
F
= (C
BAT
B
Internal Oscillator
1
1
2
1
32KX1
1
2
* C
Resonance
Frequency
Type
Serial Resistance 40 K
Quality Factor, Q
Shunt Capacitance 2 pF
Load
Capacitance, C
Temperature
Coefficient
Resistance
Resistance
Capacitance
Capacitance
2
) / (C
Parameters
1
C
+ C
1
2
R
) + C
Y
1
Real-Time Clock (RTC) and Advanced Power Control (APC)
L
PARASITIC
R
32.768 KHz
Parallel Mode
N-Cut or XY-
bar
35000
9-13 pF
User Choice
20 M
120 K
10 pF
33 pF
2
1
Values
in series with C
32KX2
C
2
To other
modules
External
Internal
defined
Toler-
User-
ance
Max
Max
Min
5%
5%
5%
5%
2
and
L
65
Oscillator Start-up
The oscillator starts to generate 32.768 KHz pulses to the
RTC and on-chip clock multiplier after about 100 ms from
when V
than V
32KX2 pin stabilizes to its final value (approximately 0.4 V
peak-to-peak around 0.7 V DC) in about 1 s.
C
achieve a high time accuracy, use crystal and capacitors
with low tolerance and temperature coefficients.
6.2.7
32.768 KHz can be applied from an external clock source,
as shown in Figure 6-2.
Connections
Connect the clock to the 32KX1 pin, leaving the oscillator
output, 32KX2, unconnected.
Signal Parameters
The signal levels should conform to the voltage level re-
quirements for 32KX1, stated in "DC ELECTRICAL CHAR-
ACTERISTICS" on page 134. The signal should have a
duty cycle of approximately 50%. It should be sourced from
a battery-backed source in order to oscillate during power-
down. This will assure that the RTC delivers updated
time/calendar information.
6.2.8
The timing generation function divides the 32.768 KHz
clock by 2
put for the seconds counter. This is performed by a divider
chain composed of 15 divide-by-two latches, as shown in
Figure 6-3.
B
Battery
1
1
can be trimmed to achieve precisely 32.768 KHz. To
Figure 6-2. External Oscillator Connections
V
CCMIN
BAT
BAT
External Oscillator
Timing Generation
C
15
F
is higher than V
to derive a 1 Hz signal, which serves as the in-
C
(3.0 V). The oscillation amplitude on the
F
C
POWER
OUT
F
=0.1 F
(32KX1)
CLKIN
Clock Generator
BATMIN
32.768 KHz
(2.4 V) or V
NC
32KX2
To other
modules
CC
External
Internal
is higher