STM32F103CBU6 datasheet(54/105 Pages) STMICROELECTRONICS

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Electrical characteristics

STM32F103x8, STM32F103xB

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DocID13587 Rev 16

Note:

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.

Caution:

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  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.

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

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

Feedback resistor



Recommended load capacitance

versus equivalent serial

resistance of the crystal (RS)

RS = 30 K

LSE driving current

VDD = 3.3 V

VIN = VSS

1.4

µA

Oscillator transconductance

µA/V

tSU(LSE)(3) Startup time

VDD is

stabilized

TA = 50 °C

1.5

TA = 25 °C

2.5

TA = 10 °C

TA = 0 °C

TA = -10 °C

TA = -20 °C

TA = -30 °C

TA = -40 °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 “Oscillator design guide for

ST microcontrollers”.

tSU(LSE) is the startup time measured from the moment it is enabled (by software) to a stabilized 32.768 kHz oscillation is

reached. This value is measured for a standard crystal and it can vary significantly with the crystal manufacturer

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