STM32F103CBT7TR datasheet(54/116 Pages) STMICROELECTRONICS

54 / 116 page

Electrical characteristics

STM32F103x8, STM32F103xB

54/116

DS5319 Rev 18

Note:

For CL1 and CL2 it is recommended to use high-quality ceramic capacitors in the 5 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 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: when choosing a resonator with a load capacitance of CL = 6 pF and 

Cstray = 2 pF, then CL1 = CL2 = 8 pF.

Figure 25. Typical application with a 32.768 kHz crystal

5.3.7

Internal clock source characteristics

The parameters given in Table 24 are derived from tests performed under ambient

temperature and VDD supply voltage conditions summarized in Table 9.

High-speed internal (HSI) RC oscillator

1. Evaluated by characterization, not tested in production, unless otherwise specified.

2. Refer to the note and caution paragraphs below the table, and to 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

ai14146

OSC32_OU T

OSC32_IN

fLSE

CL1

STM32F103xx

32.768 kH z

resonator

CL2

Resonator with

integrated capacitors

Bias

controlled

gain

Table 24. HSI oscillator characteristics(1)

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fHSI

Frequency

MHz

DuCy(HSI) Duty cycle

ACCHSI

Accuracy of the HSI

oscillator

User-trimmed with the RCC_CR

1(3)

Factory-

calibrated



(4)(5)

TA = –40 to 105 °C

–2

2.5

TA = –10 to 85 °C

–1.5

2.2

TA = 0 to 70 °C

–1.3

TA = 25 °C

–1.1

1.8

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