9.1.2

USB-PD PDO and APDO adaptation and protection

During the attach procedure, the Source and Sink verify the voltage and current, offered and requested. As

defined by the USB-PD protocol, upon cable connection the device checks the cable capabilities; in case the

cable used is not 5 A capable, the maximum current in all the PDOs and APDOs sent upon capability request is

limited to 3 A.

In case of secondary side temperature protection, the capabilities are modified depending on the temperature

level.

9.1.3

USB-PD alert management

The device implements protections such as UVP, OVP, OCP. Some, for this mode, are reported during the USB-

PD message exchange between source and sink. In some cases of this alarm type, the VBUS is automatically

disconnected and no message is sent.

The temperature is also verified and controlled. The corresponding bit into alert messages is managed.

9.1.4

Overcurrent management

The IC manages the OCP and turns off the load switch according to the USB-PD standard.

The OCP level and behavior depends on the PDO or APDO selected by sink.

•

if a PDO is selected, the OCP is set up adding a programmable percentage of the maximum current

defined on the PDO. If an OCP is detected, the load switch is turned off and Vbus is disconnected.

•

if an APDO is selected, the current is limited in CC mode. If the output voltage drops below a

programmable threshold, the power module issues a warning, and if a second threshold is bypassed,

disconnects the Vbus.

9.1.5

Undervoltage management

The IC manages the undervoltage protection depending on the PDO or APDO selected by the sink:

•

if a PDO is selected, the UVP threshold is determined as a programmable percentage of the nominal

output voltage

•

if an APDO is selected, the undervoltage is triggered by a drop below a programmable threshold while

operating in constant current mode, as described in Section 9.1.4

9.1.6

Temperature management

The ST-ONEMP device supports two temperature measurement points on the secondary side, one internal to the

device and one external using an optional NTC.

•

The internal temperature is relative to the device and, normally, the default limit is considered good for most

applications. The internal temperature sense can read between 0 ºC and +150 ºC, with an accuracy of

TACC (see Section 7 Electrical data).

•

The external temperature limit is defined by the user by connecting an external resistor divider using

an NTC. The user can program the voltage thresholds for the overtemperature fault (OTP) and warning

(WTP).

In case of temperature management, the device implements the secondary side Overtemperature Protection

(SOTP) and Warning Temperature Protection (WTP). All the temperature trip points are programmable.

Figure 11. Temperature management

Temperature

low

high

WTP

OTP

In case of overtemperature, the HARD_RESET message is sent out and the next capability proposed is only 5 V

and 500 mA. In case the OTP is confirmed for 10 seconds, the Vbus voltage is switched off. The Vbus voltage

is provided only when the secondary temperature returns below OTP-10 ºC for the internal temperature or below

OTP-Hysteresis in case of external temperature. In case the OTP is triggered, the charger functionality is restored

if either:

•

the AC line is removed, and the temperature returns into an acceptable range.

ST-ONEMP

USB-PD protocol

DS13989 - Rev 2

page 29/39