ST72325J4B5 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST72325J4B5

8-BIT MCU WITH 16 TO 60K FLASH/ROM, ADC, CSS, FIVE TIMERS, SPI, SCI, I2C INTERFACE

STMicroelectronics 

ST72325

CLOCK AND TIMING CHARACTERISTICS (Cont’d)

12.5.3 Crystal and Ceramic Resonator Oscillators

The ST7 internal clock can be supplied with four

different Crystal/Ceramic resonator oscillators. All

the information given in this paragraph are based

on characterization results with specified typical

external components. In the application, the reso-

nator and the load capacitors have to be placed as

close as possible to the oscillator pins in order to

minimize output distortion and start-up stabiliza-

tion time. Refer to the crystal/ceramic resonator

manufacturer for more details (frequency, pack-

age, accuracy...).

Symbol

fOSC

RF

CL1

CL2

Parameter

Oscillator Frequency 1)

Feedback resistor2)

Recommended load capacitance ver-

sus equivalent serial resistance of the

crystal or ceramic resonator (RS)3)

Conditions

fOSC= 1 to 2 MHz

fOSC= 2 to 4 MHz

fOSC= 4 to 8 MHz

fOSC= 8 to 16 MHz

Min

Max

Unit

1

16

MHz

20

40

kΩ

20

60

20

50

15

35

pF

15

35

Symbol

Parameter

i2

OSC2 driving current

Conditions

VDD=5V:

fOSC= 2MHz, C0 = 6pF, Cl1 = Cl2 = 68pF

fOSC= 4MHz, C0 = 6pF, Cl1 = Cl2 = 68pF

fOSC= 8MHz, C0 = 6pF, Cl1 = Cl2 = 40pF

fOSC= 16MHz, C0 = 7pF, Cl1 = Cl2 = 20pF

Typ Max

426

425

456

660

Unit

µA

Figure 76. Typical Application with a Crystal or Ceramic Resonator

WHEN RESONATOR WITH

INTEGRATED CAPACITORS

CL1

OSC1

LINEAR

AMPLIFIER

fOSC

FEEDBACK

LOOP

POWER DOWN

LOGIC

RESONATOR

VDD/2 i2

RF Ref

CL2

OSC2

ST72XXX

Notes:

1. The oscillator selection can be optimized in terms of supply current using an high quality resonator with small RS value.

Refer to crystal/ceramic resonator manufacturer for more details.

2. Data based on characterisation results, not tested in production.

3. The relatively low value of the RF resistor, offers a good protection against issues resulting from use in a humid envi-

ronment, due to the induced leakage and the bias condition change. However, it is recommended to take this point into

account if the µC is used in tough humidity conditions.

3. For CL1 and CL2 it is recommended to use high-quality ceramic capacitors in the 5-pF to 25-pF range (typ.) designed

for high-frequency applications and selected to match the requirements of the crystal or resonator. CL1 and CL2, are usu-

ally the same size. The crystal manufacturer typically specifies a load capacitance which is the series combination of CL1

and CL2. PCB and MCU pin capacitance must be included when sizing CL1 and CL2 (10 pF can be used as a rough esti-

mate of the combined pin and board capacitance).

150/193

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