STM32H747AI datasheet(141/252 Pages) STMICROELECTRONICS

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DS12930 Rev 1

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STM32H747xI/G

Electrical characteristics

221

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

characterization results obtained with typical external components specified in Table 52. 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 25 pF range (typical), designed for high-frequency applications, and selected to

match the requirements of the crystal or resonator (see Figure 23). 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. The 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.

Note:

For information on selecting the crystal, refer to the application note AN2867 “Oscillator

design guide for ST microcontrollers” available from the ST website www.st.com.

Table 52. 4-48 MHz HSE oscillator characteristics(1)

Symbol

Parameter

Operating

conditions(2)

Min

Typ

Max

Unit

Oscillator frequency

MHz

Feedback resistor

200

kΩ

IDD(HSE)

HSE current consumption

During startup(3)

VDD=3 V, Rm=30 Ω

CL=10pF@4MHz

-0.35

VDD=3 V, Rm=30 Ω

CL=10 pF at 8 MHz

-0.40

VDD=3 V, Rm=30 Ω

CL=10 pF at 16 MHz

-0.45

VDD=3 V, Rm=30 Ω

CL=10 pF at 32 MHz

-0.65

VDD=3 V, Rm=30 Ω

CL=10 pF at 48 MHz

-0.95

Gmcritmax

Maximum critical crystal gm

Startup

1.5

mA/V

tSU(4)

Start-up time

VDD is stabilized

1. Guaranteed by design.

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

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

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.

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