ST72324B datasheet(125/167 Pages) STMICROELECTRONICS

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ST72324B

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12.6.3.2 32K Flash and ROM devices

Figure 63. Typical Application with a Crystal or Ceramic Resonator (32K Flash and ROM devices)

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. The relatively low value of the RF resistor, offers a

good protection against issues resulting from use in a humid environment, due to the induced leakage and the bias con-

dition 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 es-

timate of the combined pin and board capacitance).

Symbol

Parameter

Conditions

Min

Max

Unit

fOSC

Oscillator Frequency 1)

116

MHz

Feedback resistor2)

Ω

CL1

CL2

Recommended load capacitance ver-

sus equivalent serial resistance of the

crystal or ceramic resonator (RS)

fOSC= 1 to 2 MHz

fOSC= 2 to 4 MHz

fOSC= 4 to 8 MHz

fOSC= 8 to 16 MHz

Symbol

Parameter

Conditions

Typ

Max

Unit

OSC2 driving current

VIN=VSS

fOSC= 1 to 2 MHz

fOSC= 2 to 4 MHz

fOSC= 4 to 8 MHz

fOSC= 8 to 16 MHz

160

310

610

150

250

460

910

µA

OSC2

OSC1

fOSC

CL1

CL2

ST72XXX

RESONATOR

WHEN RESONATOR WITH

INTEGRATED CAPACITORS

VDD/2

Ref

POWER DOWN

LOGIC

FEEDBACK

LOOP

LINEAR

AMPLIFIER

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