STM32F100RC datasheet(51/98 Pages) STMICROELECTRONICS

51 / 98 page

STM32F100xC, STM32F100xD, STM32F100xE

Electrical characteristics

Doc ID 15081 Rev 7

51/98

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)

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

Feedback resistor

CL1

CL2

(2)

Recommended load capacitance

versus equivalent serial

resistance of the crystal (RS)

(3)

RS = 30 KΩ

LSE driving current

VDD = 3.3 V

VIN = VSS

1.4

µA

Oscillator transconductance

µA/V

tSU(LSE)

(4)

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

Based on characterization, not tested in production.

Refer to the note and caution paragraphs above the table.

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

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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