STM32F427AI datasheet(96/239 Pages) STMICROELECTRONICS

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Electrical characteristics

STM32F427xx STM32F429xx

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DocID024030 Rev 9

6.3.2

VCAP1/VCAP2 external capacitor

Stabilization for the main regulator is achieved by connecting an external capacitor CEXT to

the VCAP1/VCAP2 pins. CEXT is specified in Table 19.

Figure 24. External capacitor CEXT

1. Legend: ESR is the equivalent series resistance.

Table 18. Limitations depending on the operating power supply range

Operating

power supply

range

ADC operation

Maximum Flash

memory access

frequency with

no wait states

(fFlashmax)

Maximum HCLK

frequency vs Flash

memory wait states

(1)(2)

I/O operation

Possible Flash

memory

operations

VDD =1.7 to

2.1 V(3)

Conversion time

up to 1.2 Msps

20 MHz(4)

168 MHz with 8 wait

states and over-drive

OFF

No I/O

compensation

8-bit erase and

program

operations only

VDD = 2.1 to

2.4 V

Conversion time

up to 1.2 Msps

22 MHz

180 MHz with 8 wait

states and over-drive

No I/O

compensation

16-bit erase and

program

operations

VDD = 2.4 to

2.7 V

Conversion time

up to 2.4 Msps

24 MHz

180 MHz with 7 wait

states and over-drive

I/O compensation

works

16-bit erase and

program

operations

VDD = 2.7 to

3.6 V(5)

Conversion time

up to 2.4 Msps

30 MHz

180 MHz with 5 wait

states and over-drive

I/O compensation

works

32-bit erase and

program

operations

1. Applicable only when the code is executed from Flash memory. When the code is executed from RAM, no wait state is

required.

2. Thanks to the ART accelerator and the 128-bit Flash memory, the number of wait states given here does not impact the

execution speed from Flash memory since the ART accelerator allows to achieve a performance equivalent to 0 wait state

program execution.

3. VDD/VDDA minimum value of 1.7 V is obtained with the use of an external power supply supervisor (refer to Section 3.17.2:

Internal reset OFF).

4. Prefetch is not available.

5. The voltage range for USB full speed PHYs can drop down to 2.7 V. However the electrical characteristics of D- and D+

pins will be degraded between 2.7 and 3 V.

Table 19. VCAP1/VCAP2 operating conditions(1)

1. When bypassing the voltage regulator, the two 2.2 µF VCAP capacitors are not required and should be

replaced by two 100 nF decoupling capacitors.

Symbol

Parameter

Conditions

CEXT

Capacitance of external capacitor

2.2 µF

ESR

ESR of external capacitor

< 2

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