STUSB4700 datasheet(11/32 Pages) STMICROELECTRONICS

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STUSB4700

Block descriptions

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The policy engine interprets the device policy manager’s input in order to implement policy

for port and directs the protocol layer to send appropriate messages.

3.5

Device policy manager

The device policy manager is managing the power resources.

3.6

VBUS power path control

3.6.1

VBUS monitoring

The VBUS monitoring block supervises (from the VBUS_SENSE input pin) the VBUS voltage

on the USB Type-C receptacle side.

This block is used to check that VBUS is within a valid voltage range:



To establish a valid source-to-sink connection according to USB Type-C standard

specification



To enable safely the VBUS power path through VBUS_EN_SRC pin

It allows detection of unexpected VBUS voltage conditions such as undervoltage or

overvoltage relative to the valid VBUS voltage range. When such conditions occur, the

STUSB4700 reacts as follows:



At attachment, it prevents the source-to-sink connection and the VBUS power path

assertion



After attachment, it deactivates the source-to-sink connection and disables the VBUS

power path. The device goes into error recovery state.

The VBUS voltage value is automatically adjusted at attachment and at each PDO transition.

The monitoring is then disabled during T_PDO_transition (default 280 ms changed through

NVM programming). Additionally, if a transition occurs to a lower voltage, the discharge

path is activated during this time.

The valid VBUS voltage range is defined from the VBUS nominal voltage by a high threshold

voltage and a low threshold voltage whose minimal values are respectively VBUS+5% and

VBUS-5%. The nominal threshold limits can be shifted by a fraction of VBUS from +1% to

+15% for the high threshold voltage and from -1% to -15% for the low threshold voltage.

This means the threshold limits can vary from VBUS+5% to VBUS+20% for the high limit and

from VBUS-5% to VBUS-20% for the low limit.

The threshold limits are preset by default in the NVM with different shift coefficients (see

Section 8.3: "Electrical and timing characteristics"). The threshold limits can be changed

independently through NVM programming (see Section 4: "User-defined startup

configuration") and also by software during attachment through the I2C interface (see

Section 6: "I²C register map").

3.6.2

VBUS discharge

The monitoring block handles also the internal VBUS discharge path connected to the

VBUS_SENSE input pin. The discharge path is activated at detachment, or when the

device goes into the error recovery state (see Section 3.8: "Hardware fault management").

The VBUS discharge path is enabled by default in the NVM and can be disabled through

NVM programming only (see Section 4: "User-defined startup configuration"). Discharge

time duration (T_PDO_transition and T_Transition to 0 V) are also preset by default in the

NVM (see Section 8.3: "Electrical and timing characteristics"). The discharge time duration

can be changed through NVM programming (see Section 4: "User-defined startup

configuration") and also by software through the I2C interface (see Section 6: "I²C register

map").

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