AN2556 datasheet(6/35 Pages) STMICROELECTRONICS

6 / 35 page

Modified features

AN2556

6/35

1.1.3

Pin 56

In the ST10F269Zx, a decoupling capacitor of 330nF minimum has to be connected

between pin 56 (named DC1) and the nearest VSS pin.

In the ST10F273Z4, pin 56 is named V18 and a capacitor with a value between 10nF

minimum and 100nF maximum must be connected between it and the nearest VSS pin.

Hardware impacts

The capacitor value may need to be changed. As the value is much lower, the footprint of

the capacitor might be smaller and thus a modification of the PCB may be needed.

Software impacts

None.

1.1.4

Pin 99

In the ST10F269Zx, pin 99 is named EA and when it is reset it is used to select the start

from internal Flash or external memory.

Pin 99 now has an additional function in the ST10F273Z4 which is to provide the 5V power

supply to the device in standby mode (new power saving mode). It is therefore named EA-

VSTBY.

Hardware impacts

Modification depends on the previous use of the ST10F269Zx and on the use or non-use of

Standby mode.

For an application that does not use Standby mode, no change is required on the PCB. If the

new application uses the Standby mode, the EA-VSTBY pin must be separated from the

common 5V and have a specific supply path.

Software impacts

None.

1.1.5

Pins 143 and 144

These pins are a VSS-VDD pair in the ST10F269Zx. In the ST10F273Z4, they are now used

as an XTAL3-XTAL4 pair for connection to an optional 32 kHz crystal to clock the Real Time

Clock during Power-Down.

Hardware impacts

The PCB must be redesigned.

In case the optional 32 kHz is not used:

●

XTAL3 must be linked to Ground as was previously the case for ST10F269Zx.

●

XTAL4 can be left open or it may be connected to Ground via a capacitor to reduce the

potential effect of RF noise which could be propagated inside the device if it is left

floating.

AN2556 Datasheet(PDF) 6 Page - STMicroelectronics

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