LC87FBG08A

No.A2046-26/30

Characteristics of a Sample Subsystem Clock Oscillator Circuit

Given below are the characteristics of a sample subsystem clock oscillation circuit that are measured using a Our

designated oscillation characteristics evaluation board and external components with circuit constant values with which

the oscillator vendor confirmed normal and stable oscillation.

Table 2 Characteristics of a Sample Subsystem Clock Oscillator Circuit with a Crystal Oscillator

EPSON TOYOCOM

Nominal

Frequency

Type

Oscillator

Name

Circuit Constant

Operating

Voltage

Range

[V]

Oscillation

Stabilization Time

Remarks

C1

[pF]

C2

[pF]

Rf

[

Ω]

Rd

[

Ω]

typ

[s]

max

[s]

32.768kHz

SMD

MC-306

9

9

Open

330k

1.8 to 5.5

1.4

4.0

Applicable CL value =

7.0pF

SEIKO INSTRUMENTS

Nominal

Frequency

Type

Oscillator

Name

Circuit Constant

Operating

Voltage

Range

[V]

Oscillation

Stabilization Time

Remarks

C1

[pF]

C2

[pF]

Rf

[

Ω]

Rd

[

Ω]

typ

[s]

max

[s]

32.768kHz

SMD

SSP-T7-F

18

22

Open

330k

1.8 to 5.5

0.75

2.0

Applicable CL value =

12.5pF

The oscillation stabilization time refers to the time interval that is required for the oscillation to get stabilized after VDD

goes above the operating voltage lower limit (see Figure 3).

• The time interval that is required for the oscillation to get stabilized after the instruction for starting the subclock

oscillation circuit is executed.

• The time interval that is required for the oscillation to get stabilized after the Hold mode, under the state which

the subclock oscillation is enabled, is reset and oscillation is started.

(Notes on the implementation of the oscillator circuit)

• Oscillation is influenced by the circuit pattern layout of printed circuit board. Place the oscillation-related

components as close to the CPU chip and to each other as possible with the shortest possible pattern length.

• Keep the signal lines whose state changes suddenly or in which large current flows as far away from the oscillator

circuit as possible and make sure that they do not cross one another.

• Be sure to insert a current limiting resistor (Rd) so that the oscillation amplitude never exceeds the input voltage

level that is specified as the absolute maximum rating.

• The oscillator circuit constants shown above are sample characteristic values that are measured using the Our

designated oscillation evaluation board. Since the accuracy of the oscillation frequency and other characteristics vary

according to the board on which the IC is installed, it is recommended that the user consult the resonator vendor for

oscillation evaluation of the IC on a user's production board when using the IC for applications that require high

oscillation accuracy. For further information, contact your resonator vendor or Our company sales representative

serving your locality.

• It must be noted, when replacing the flash ROM version of a microcontroller with a mask ROM version, that their

operating voltage ranges may differ even when the oscillation constant of the external oscillator is the same.

Figure 1 CF and XT Oscillator Circuit

Figure 2 AC Timing Measurement Point

0.5VDD

Rf

Rd

CF1/XT1

CF2/XT2

C2

CF/X’tal

C1