STM32WL33C8 datasheet(12/91 Pages) STMICROELECTRONICS

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3.5

Power supply management

3.5.1

SMPS step-down converter

The device integrates a step-down converter to improve low power performance when the VDD (aka VDDIO)

voltage is high enough.

The SMPS output voltage can be programmed from 1.2 V to 2.4 V with a granularity of 100 mV. The SMPS output

voltage can be controlled by the PWRC_CR5.SMPSLVL[3:0] register.

The relation between the SMPSLVL and the VOUT of the SMPS is given by Table 2:

Table 2. SMPS output voltage

SMPSLV

VOUT

Min. VBATT

1.2 V

1.95 V

1.2 V

1.95 V

1.2 V

1.95 V

1.3 V

1.95 V

1.4 V

2.0 V

1.5 V

2.0 V

1.6 V

2.15 V

1.7 V

2.2 V

1.8 V

2.3 V

1.9 V

2.45 V

2.0 V

2.6 V

2.1 V

2.7 V

2.2 V

2.8 V

2.3 V

2.8 V

2.4 V

2.9 V

2.4 V

2.9 V

It is internally clocked at 4 MHz or 8 MHz. It can be clocked at a frequency in-between 4 MHz and 8 MHz by

means of the KRM feature. In this case the SMPS can be clocked at System Clock divided by 8 to 16 by unitary

steps. This feature is useful to avoid that the channel to be received is at a frequency that is an integer multiple of

the SMPS clock.

The device can operate without the internal SMPS either by using a dedicated hardware setting, or by using the

bypass-on-the-fly (BOF) feature. The bypass-on-the-fly permits internal connection of the SMPS output to the

battery via a current-limited switch (Static mode), or bypass of the SMPS by the use of an internal regulator

(dynamic). In both modes the SMPS is off while the bypass-on-the-fly is operating, and a programmable current

limitation is provided. The static mode connects the SMPS output to the battery after the first start-up of the

STM32WL33xx, and the connection is maintained until a reset occurs. In this case, the transmission is limited to

+14dBm. The dynamic mode bypasses the SMPS with a regulator. For instance, this can be done dynamically to

use the SMPS during transmission and to bypass the SMPS via a regulator during reception.

The SMPS has the following possible configurations:

•

SMPS_ON

–

the VFBSD pin of the SMPS outputs a regulated voltage (from 1.2V to 2.4V)

–

the SMPS needs a clock.

•

No SMPS

–

VFBSD pin must be connected or to an external supply or to VDD

–

VLXSD pin must be floating

–

the SMPS does not need a clock

STM32WL33xx

Functional overview

DS14221 - Rev 5

page 12/91

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