S2-LPS datasheet(19/73 Pages) STMICROELECTRONICS

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The S2-LPS PM can be configured by SPI (BYPASS_LDO field in PM_CONFIG [1] register) in two main modes:

High performance mode (HPM)

Low power mode (LPM)

In HPM all available LDOs supplied from SMPS are used, to get the best possible isolation and minimum

low-frequency noise level and SMPS ripple. SMPS must be set to 1.4 V at least.

In LPM the LDOs connected to the SMPS are by-passed and SMPS must be configured to provide 1.2 V output

level to increase the regulation efficiency but with reduced isolation and higher low-frequency noise and SMPS

ripple.

The load inductor of the SMPS has to have the following characteristics:

•

A typical 10 µH nominal value +/-10%

•

A rated current of 100 mA minimum

•

A DC resistance as low as possible (to guarantee maximum efficiency of the SMPS block), around 1 Ohm is

a typically good value, but the lower the better

4.2

Power-On-Reset

The Power-On-Reset (POR) circuit generates a reset pulse upon power-up which is used to initialize the entire

digital logic. Power-on-reset senses VBAT voltage.

The S2-LPS provides an automatic POR circuit, which generates an internal RESETN (active low) level for a time

TRESET, after the VBAT reaches the reset release voltage threshold VRRT, as shown in Figure 6. Power-On-Reset

timing and limits. The same reset pulse is generated after a step-down on the input pin SDN (VDD>VRRT). This

signal is available on the GPIO0 pin.

Figure 6. Power-On-Reset timing and limits

The parameters VRRT and TRESET are fixed by design in order to guarantee a reliable reset procedure of the

state machine. In addition, all the registers are initialized to their default values.

A software command SRES is also available, it generates an internal but partial resetting of the S2-LPS.

Table 29. POR parameters

Parameter

Comment

Min.

Typ.

Max.

Unit

Reset start-up threshold voltage

0.5

Hold pulse width (Thold, figure below)

For SDN to be effective

µs

S2-LPS

Power-On-Reset

DS13831 - Rev 1

page 19/73

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