Power Receiver Interface

The flow-chart visible in Figure 3 reports the whole process leading to a power transfer in Base Power Profile

(BPP), the only power profile supported by STWLC68 due to a maximum output power of 5 W (1.0 A @ 5 V).

Ping

Identification &

Configuration

Power Transfer

Extended Digital Ping

Power Transfer Contract established

Selection

Apply Power Signal

No Response / Abort Digital Ping

Power Transfer Contract Violation /

Unexpected Packet /

Timeout

No Power Transfer Contract /

Unexpected Packet /

Transmission Error / Timeout

Power Transfer Complete

In case of Qi-mode the STWLC68 goes autonomously through Selection, Ping, Identification & Configuration

phases, entering Power Transfer phase if no error occurs. During the Power Transfer phase, the device sends

Received-Power and Control-Error packets periodically as feedback information for the transmitter. If a critical

event like over-voltage, over-current or over-temperature occurs, the STWLC68 automatically sends the End-

Power-Transfer packet.

When the Power Transfer is up and running, the End-Power-Transfer packet (with any response value) or any

custom packet (e.g. Proprietary packet or Charge-Status packet) can be sent to the transmitter simply through

response from the transmitter) or no reply at all: if a response is received, the content is captured and stored in

Important notes:

•

Changing the output voltage must respect the overall system design (selected coil, transmitter type, etc.).

•

Output load transient response strongly depends on correct design of the output capacitors. Severe load

transients may lead to temporary output voltage collapse due to the overall TX-RX response time.

•

A minimum output load significantly helps in increasing the signal-to-noise ratio during digital pin and it is

advisable to ensure interoperability with all transmitters. For this purpose, the STWLC68 allows the user

to set a dummy load (reservoir current) that is dynamically managed to fade-out when an output load is

applied.

•

The initial load at power-up should not exceed 2.5 W, smoothly ramping-up to full power subsequently.

5.8

I2C interface

The STWLC68 can operate fully independently, i.e. without being interfaced with any host controller. In

applications in which the STWLC68 has to be part of the peripherals managed by the host system, the two

SDA and SCL pins could be connected to the existing I²C bus.

Thedevice works as an I²C slave and supports both standard (100 kbit/s) and fast (400 kbit/s) data transfer

modes.

Through the I²C interface, maximum device flexibility is obtained and full access to the internal resources is

possible. The host controller typically polls for device status and power transfer operation, demands for custom

commands execution or reconfigures the default parameters.

STWLC68

I2C interface

DS13131 - Rev 3

page 13/32