LC87FBH08A
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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
[]
Rd
[]
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
[]
Rd
[]
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 V
DD
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
0.5V
DD
Rf
Rd
CF1/XT1
CF2/XT2
C2
CF/X’tal
C1
