STM32L475RG datasheet(112/193 Pages) STMICROELECTRONICS

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Electrical characteristics

STM32L475xx

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DocID027692 Rev 2

High-speed external clock generated from a crystal/ceramic resonator

The high-speed external (HSE) clock can be supplied with a 4 to 48 MHz crystal/ceramic

resonator oscillator. All the information given in this paragraph are based on design

simulation results obtained with typical external components specified in Table 46. In the

application, the resonator and the load capacitors have to be placed as close as possible to

the oscillator pins in order to minimize output distortion and startup stabilization time. Refer

to the crystal resonator manufacturer for more details on the resonator characteristics

(frequency, package, accuracy).

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

5 pF to 20 pF range (typ.), designed for high-frequency applications, and selected to match

the requirements of the crystal or resonator (see Figure 15). 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. PCB and MCU pin capacitance must be included (10 pF

can be used as a rough estimate of the combined pin and board capacitance) when sizing

CL1 and CL2.

Table 46. HSE oscillator characteristics(1)

1. Guaranteed by design.

Symbol

Parameter

Conditions(2)

2. Resonator characteristics given by the crystal/ceramic resonator manufacturer.

Min

Typ

Max

Unit

fOSC_IN

Oscillator frequency

MHz

Feedback resistor

200

kΩ

IDD(HSE) HSE current consumption

During startup(3)

3. This consumption level occurs during the first 2/3 of the tSU(HSE) startup time

5.5

VDD = 3 V,

Rm = 30 Ω,

CL = 10 pF@8 MHz

-0.44

VDD = 3 V,

Rm = 45 Ω,

CL = 10 pF@8 MHz

-0.45

VDD = 3 V,

Rm = 30 Ω,

CL = 5 pF@48 MHz

-0.68

VDD = 3 V,

Rm = 30 Ω,

CL = 10 pF@48 MHz

-0.94

VDD = 3 V,

Rm = 30 Ω,

CL = 20 pF@48 MHz

-1.77

Maximum critical crystal

transconductance

Startup

1.5

mA/V

tSU(HSE)(4)

4. tSU(HSE) is the startup time measured from the moment it is enabled (by software) to a stabilized 8 MHz

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

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