S35390A datasheet(39/51 Pages) SII

39 / 51 page

FOR AUTOMOTIVE 105°C OPERATION 2-WIRE REAL-TIME CLOCK

Rev.2.2_00

S-35390A H Series

Seiko Instruments Inc.



Adjustment of Oscillation Frequency

1. Configuration of crystal oscillation circuit

Since the crystal oscillation circuit is sensitive to external noise (the clock accuracy is affected), the following measures

are essential for optimizing the configuration.

• Place the S-35390A H Series crystal oscillator, and external capacitor (Cg) as close to each other as possible.

• Increase the insulation resistance between pins and the substrate wiring patterns of XIN and XOUT.

• Do not place any signal or power lines close to the crystal oscillation circuit.

• Locating the GND layer immediately below the crystal oscillation circuit is recommended.

• Locate the bypass capacitor adjacent to the power supply pin of the S-35390A H Series.

S-35390A H Series

XOUT

XIN

Rf = 100 M

 (typ.)

Rd = 100 k

 (typ.)

Cd = 8 pF (typ.)

Parasitic capacitance*3

Crystal oscillator: 32.768 kHz

Parasitic capacitance*3

CL = 6 pF*1

Cg = None*2 to 9.1 pF

*1.

When setting the value for the crystal oscillator's CL as 7 pF, connect Cd externally if necessary.

*2.

The crystal oscillation circuit operates even when Cg is not connected. Note that the oscillation frequency is in the

direction that it advances.

*3.

Design the board so that the parasitic capacitance is within 5 pF.

Figure 49 Connection Diagram 1

XIN

XOUT

VSS

S-35390A H

Series

Locate the GND layer in the

layer immediately below

Crystal

oscillator

Figure 50 Connection Diagram 2

Caution 1. When using the crystal oscillator with a CL exceeding the rated value (7 pF) (e.g: CL = 12.5 pF),

oscillation operation may become unstable. Use a crystal oscillator with a CL 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 Cg. When configuring a crystal oscillation

circuit, pay sufficient attention for them.

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