5.6

GPIOx and INTB pins

The GPIO0 through GPIO5 pins are programmable general-purpose I/O pins whose functions can be assigned in

OTP memory. These pins can be configured both as inputs and outputs (either push-pull or open-drain) according

to the selected function.

The INTB pin is an interrupt output line that can be associated to any internal interrupt condition and used to

inform the host system about specific events. The INTB pin can be programmed to be push-pull or open-drain

type as well.

The following table reports the available functions that can be assigned by writing the corresponding GPIOx-FS

register.

GPIO function and type

GPIOx-FS register

Description

GPIOF_NONE

I

0x00

No function

GPIOF_XINT_OD

O

0x03

Interrupt signal status (inverted), open-drain

GPIOF_XINT_PP

O

0x04

Interrupt signal status (inverted), push-pull

GPIOF_OUT_INH

I

0x05

Output voltage inhibit control (input):

low = enable VOUT, high = inhibit VOUT

GPIOF_OUT_MON

O

0x06

Output status monitor

low = VOUT disabled, high = VOUT enabled

GPIOF_OUT_XMON

O

0x07

Output status monitor (inverted)

low = VOUT enabled, high = VOUT disabled

GPIOF_OUT_XMON_OD

O

0x08

Output status monitor (inverted, open-drain)

low = VOUT enabled, high = VOUT disabled

GPIOF_ADC_TICK

O

0x0F

ADC sampling toggling ticker (debug)

GPIOF_CORE_XRDY

O

0x1D

Digital core ready (inverted). If low, core and I2C

interface are ready.

Note:

the INTB pin is also used as auxiliary control signal by the Graphical User Interface (GUI) during OTP flashing.

This signal must be conveniently routed to the programming connector in the application (see evaluation boards

as a reference)

5.7

Wireless power interface

The blocks that refer to the wireless power interface are the synchronous rectifier, the main LDO linear regulator

and the ASK modulator, as well as the digital core as supervisor. As previously mentioned, the power transfer

from the transmitter to the receiver is actually the result of a procedure that involves different phases.

In brief, a power transfer begins after the transmitter has properly detected a valid receiver and a specific

communication has been established between the two parts. Without entering the details of the different phases,

the basic sequence of events taking place when a receiver is properly placed on the transmitting coil are

summarized as:

•

Analog ping: this is the initial step of the so-called “selection phase”. A brief AC burst is periodically

generated by the transmitter in order to detect the presence of a potential receiver on its transmitting

surface. Through analog ping the transmitter could eventually be able to discriminate foreign objects.

•

Digital ping: this step is an interrogation session based on a more energetic AC burst during which the

potential receiver is expected to reply through amplitude shift-keying (ASK) modulation.

•

Identification & configuration: this is the following step aiming to identify the receiver and to gather

information about its power transfer capability. The transmitter generates a so-called “Power Transfer

Contract” tailoring some parameters that will characterize the following power transfer phase.

•

Power transfer: this is the final step, where the transmitter initially increases and subsequently modulates the

transmitted power in response to the control (feedback) data from the receiver.

STWLC68

GPIOx and INTB pins

DS13131 - Rev 3

page 12/32