CD00161566 Datasheet, PDF(54/105 Page) STMicroelectronics – nullMedium-density performance line ARM-based 32-bit MCU

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CD00161566 Datasheet, PDF (54/105 Pages) STMicroelectronics – nullMedium-density performance line ARM-based 32-bit MCU

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Electrical characteristics

STM32F103x8, STM32F103xB

Symbol

Table 23. LSE oscillator characteristics (fLSE = 32.768 kHz)(1) (2)

Parameter

Conditions

Min Typ Max Unit

Feedback resistor

Mï

Recommended load capacitance

versus equivalent serial

resistance of the crystal (RS)

RS = 30 Kï

15 pF

LSE driving current

VDD = 3.3 V

VIN = VSS

1.4 ÂµA

Oscillator transconductance

- ÂµA/V

TA = 50 Â°C

1.5

TA = 25 Â°C

2.5

TA = 10 Â°C

tSU(LSE)(3) Startup time

VDD is

stabilized

TA = 0 Â°C

TA = -10 Â°C

TA = -20 Â°C

TA = -30 Â°C

TA = -40 Â°C

1. Based on characterization, not tested in production.

2. Refer to the note and caution paragraphs below the table, and to the application note AN2867 âOscillator design guide for

ST microcontrollersâ.

rteSaUc(LhSeEd).

is the startup

This value is

time measured

measured for a

from the moment it is enabled (by software)

standard crystal and it can vary significantly

to a stabilized 32.768 kHz oscillation

with the crystal manufacturer

Note:

Caution:

For CL1 and CL2 it is recommended to use high-quality ceramic capacitors in the 5 pF to

15 pF range selected to match the requirements of the crystal or resonator. CL1 and CL2, are

usually the same size. The crystal manufacturer typically specifies a load capacitance which

is the series combination of CL1 and CL2.

Load capacitance CL has the following formula: CL = CL1 x CL2 / (CL1 + CL2) + Cstray where

Cstray is the pin capacitance and board or trace PCB-related capacitance. Typically, it is

between 2 pF and 7 pF.

To avoid exceeding the maximum value of CL1 and CL2 (15 pF) it is strongly recommended

to use a resonator with a load capacitance CL ï£ 7 pF. Never use a resonator with a load

capacitance of 12.5 pF.

Example: if you choose a resonator with a load capacitance of CL = 6 pF, and Cstray = 2 pF,

then CL1 = CL2 = 8 pF.

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