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_Transition_To_PDO (default 288 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. It 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 start-up 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, during transition to a lower PDO voltage, or when the device goes
into the error recovery state (see Section 3.8 Hardware fault management).
The automatic VBUS discharge path feature is enabled by default in the NVM and can be disabled through NVM
programming only (see Section 4 User-defined start-up configuration). Discharge time duration
(T_Transition_To_PDO and T_Transition_To_0V) 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 start-up configuration) and also by software through the I2C interface (see Section 6 I²C register
map).
3.6.3 VBUS power path assertion
The STUSB4700 can control the assertion of the VBUS power path on USB Type-C port, directly or indirectly,
through VBUS_EN_SRC pin.
The following table summarizes the configurations of the STUSB4700 and the operation conditions that determine
the electrical value of the VBUS_EN_SRC pin during system operations.
STUSB4700
VBUS power path control
DS11977 - Rev 4 page 10/43