3.3

Auto-run mode

The STUSB4500 implements a hardcoded decision algorithm that allows the device to negotiate in autonomous

way a power delivery transaction with a source according to the PDO (power data objects) profiles programmed in

the NVM.

It makes the STUSB4500 a plug-and-play, autonomous and effective solution to develop USB PD sink systems

operating in standalone.

3.3.1

Sink PDOs configuration

The STUSB4500 features up to 3 sink PDOs (SNK_PDO). The value of each PDO is defined in the NVM (see

Section 5 Start-up configuration).

Sink PDO #

Comment

Priority

Description

PDO1

Mandatory

Low

Defines the default power configuration

PDO2

Optional

Medium

Defines the intermediate power configuration

PDO3

Optional

High

Defines the highest power configuration (if any)

PDO voltage configuration:

•

PDO1 voltage is fixed to 5 V by hardware

•

PDO2 and PDO3 voltages are programmable by NVM from 5 V to 20 V by steps of 50 mV as defined in the

USB PD standard specification (see Section 5 Start-up configuration)

PDO current configuration:

•

The current of each PDO is programmable by NVM through look-up table see (Section 5 Start-up

configuration)

•

15 predefined values are set in the look-up table from 0.5 A to 5 A

•

1 custom value can be programmed in the look-up table from 10 mA to 5 A by steps of 10 mA as defined in

the USB PD standard specification. This value is common to all PDOs if used

3.3.2

Decision algorithm description

The decision algorithm compares each SNK_PDOi with the SRC_PDOj capabilities received from the source.

The comparison starts from the SNK_PDO with the highest priority to the SNK_PDO with the lowest priority. The

voltage is compared first, the current afterwards.

A match occurs when both conditions are met:

1.

V(SNK_PDOi) = V(SRC_PDOj)

2.

I(SNK_PDOi) ≤ I(SRC_PDOj)

The comparison loop stops at the first match. The remaining SRC_PDOj are not compared and the SNK_PDOi

with lower priority are discarded.

In case of match:

•

An RDO (request data object) message is formed with matched voltage V(SNK_PDOi) as operating voltage,

related I(SNK_PDOi) current as operating current and I(SRC_PDOj) current from matched SRC_PDOj as

maximum current

•

The RDO message is sent to the source for evaluation and acceptance by the source prior the transition to

matched PDO voltage by the source and the reception of PS_READY message by the sink

In case of no match:

•

At the end of the comparison loop, if no match happens, the USB PD negotiation ends with an explicit USB

PD contract at 5 V

•

An RDO message is sent to the source with capability mismatch enabled, operating current set to current

value from source PDO at 5 V, and maximum current set to I(SNK_PDO1)

STUSB4500

Auto-run mode

DS12499 - Rev 2

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