S-35392A Datasheet, PDF (37/47 Pages) Seiko Instruments Inc – 2-WIRE REAL-TIME CLOCK

Rev.1.3_00
2-WIRE REAL-TIME CLOCK
S-35392A
„ Adjustment of Oscillation Frequency
1. Configuration of oscillator
Since crystal oscillation is sensitive to external noise (the clock accuracy is affected), the following measures are
essential for optimizing the oscillation configuration.
(1) Place the S-35392A, crystal oscillator, and external capacitor (C_g) as close to each other as possible.
(2) Increase the insulation resistance between pins and the substrate wiring patterns of XIN and XOUT.
(3) Do not place any signal or power lines close to the oscillator.
(4) Locating the GND layer immediately below the oscillator is recommended.
(5) Locate the bypass capacitor adjacent to the power supply pin of the S-35392A.
Parasitic capacitance^*3
XIN
Rf
Cg
Crystal oscillator: 32.768 kHz
CL = 6 pF^*1
XOUT
Rd
Cg = None^*2 to 9.1 pF
Parasitic capacitance^*3
Cd
Oscillator internal constant
standard values:
Rf = 100 MΩ
Rd = 100 kΩ
Cd = 8 pF
S-35392A
*1. When setting the value for the crystal oscillator’s C_L as 7 pF, connect C_d externally if necessary.
*2. Design the board so that the parasitic capacitance is 5 pF.
*3. The oscillator operates unless C_g is not connected. Note that the oscillation frequency is in the direction that it
advances.
Figure 45 Connection Diagram 1
Crystal oscillator
C_g
1
S-35392A ₈
2 XOUT
7
3 XIN
6
4 ^VSS
5
Locate the GND layer in the
layer immediately below
Figure 46 Connection Diagram 2
Caution
1. When using the crystal oscillator with a C_L exceeding the rated value (7 pF) (e.g : C_L = 12.5 pF),
oscillation operation may become unstable. Use a crystal oscillator with a C_L value of 6 pF or 7 pF.
2. Oscillation characteristics is subject to the variation of each component such as substrate parasitic
capacitance, parasitic resistance, crystal oscillator, and C_g. When configuring an oscillator, pay
sufficient attention for them.
Seiko Instruments Inc.
37