STM32F100C4 datasheet(48/84 Pages) STMICROELECTRONICS

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Electrical characteristics

STM32F100x4, STM32F100x6, STM32F100x8, STM32F100xB

48/84

Doc ID 16455 Rev 2

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.

Figure 20.

Typical application with a 32.768 kHz crystal

Table 22.

LSE oscillator characteristics (fLSE = 32.768 kHz)

(1)

Based on characterization, not tested in production.

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

Feedback resistor



CL1

CL2

(2)

Refer to the note and caution paragraphs above the table.

Recommended load capacitance

versus equivalent serial

resistance of the crystal (RS)

(3)

The oscillator selection can be optimized in terms of supply current using an high quality resonator with

small RS value for example MSIV-TIN32.768 kHz. Refer to crystal manufacturer for more details

RS = 30 K

LSE driving current

VDD = 3.3 V

VIN = VSS

1.4

µA

Oscillator transconductance

µA/V

tSU(LSE)

(4)

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 resonator and it can vary

significantly with the crystal manufacturer

Startup time

VDD is stabilized

ai14129b

OSC32_OU T

OSC32_IN

fLSE

CL1

STM32F10xxx

32.768 KH z

resonator

Resonator with

integrated capacitors

Bias

controlled

gain

CL2

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