STUSB4500 datasheet(12/41 Pages) STMICROELECTRONICS

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3.3.3

Requesting maximum source current

Thanks to dedicated NVM bit “REQ_SRC_CURRENT”, the operating current informed in the RDO message,

when a matching PDO is found, can be set either to the current value from the matched sink PDO (default) or to

the current value from the matched source PDO.

Requesting current value from the matched source PDO is useful for a sink that can benefit from higher power

capability than originally required in order to increase its performance. This implies for the source to allocate a

power reserve as stated in the USB PD standard specification.

In case the sink is not able to consume more power than requested, this option must not be used. It avoids

allocating by the source a power reserve that is not used, thus limiting the overall power system optimization.

3.3.4

Decision algorithm application with examples

The following capabilities from the source have been considered to study the negotiation result for different sink

PDO configuration cases with the STUSB4500:

•

SRC_PDO1 = 5 V, 3 A

•

SRC_PDO2 = 9 V, 3 A

•

SRC_PDO3 = 15 V, 2 A

Table 9. Decision algorithm results for different cases

Case

Configured sink capabilities

Result REQ_SRC_CURRENT = 0b

Result REQ_SRC_CURRENT = 1b

SNK_PDO2 = 9 V, 2.5 A

SNK_PDO1 = 5 V, 3 A

Match: RDO = 9 V, 2.5 A, 3 A

Not compared

Match: RDO = 9 V, 3 A, 3 A

Not compared

SNK_PDO3 = 9.1 V, 2.9 A

SNK_PDO2 = 8.9 V, 2.9 A

SNK_PDO1 = 5 V, 3 A

No match

Match: RDO = 5 V, 3 A, 3 A

No match

Match: RDO = 5 V, 3 A, 3 A

SNK_PDO3 = 15 V, 2.1 A

SNK_PDO2 = 9 V, 2.5 A

SNK_PDO1 = 5 V, 3 A

No match

Match: RDO = 9 V, 2.5 A, 3 A

Not compared

No match

Match: RDO = 9 V, 3 A, 3 A

Not compared

SNK_PDO3 = 15.1 V, 2 A

SNK_PDO2 = 15 V, 1 A

SNK_PDO1 = 5 V, 3 A

No match

Match: RDO = 15 V, 1 A, 2 A

Not compared

No match

Match: RDO = 15 V, 2 A, 2 A

Not compared

SNK_PDO2 = 15 V, 3 A

SNK_PDO3 = 9 V, 1 A

SNK_PDO1 = 5 V, 1 A

No match

Match: RDO = 9 V, 1 A, 3 A

Not compared

No match

Match: RDO = 9 V, 3 A, 3 A

Not compared

3.4

VBUS power path control

3.4.1

VBUS monitoring

The VBUS monitoring block supervises from the VBUS_VS_DISCH input pin the VBUS voltage on the USB Type-C

receptacle side.

It is used to check that VBUS is within a valid voltage range to establish a valid source-to-sink connection and to

enable safely the VBUS power path through the VBUS_EN_SNK 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 STUSB4500 reacts as follows:

•

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

asserted

•

After attachment, it goes into unattached state and it disables the VBUS power path

STUSB4500

VBUS power path control

DS12499 - Rev 2

page 12/41

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