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1/18/2017

2016-11-0004

PT0493-4

26

PI5USB2546

CDP/SDP Auto Switch

PI5USB2546 is equipped with a CDP/SDP auto-switch feature to support some popular phones in the market that are not

compliant to the BC1.2 specification, as they fail to establish data connection in CDP mode. These phones use primary

detection (used to distinguish between an SDP and different types of Charging Ports) to only identify ports as SDP (data / no

charge) or DCP (no data / charge). They do not recognize CDP (data /charge) ports. When connected to a CDP port, these

phones classify the port as a DCP and will only charge. Since charging ports are configured as CDP when the computer is in S0,

users do not get the expected data connection.

To remedy this problem PI5USB2546 employs a CDP/SDP Auto Switch scheme to ensure these BC1.2 non-compliant phones

will establish data connection by following below steps:



The PI5USB2546 will determine when a non-compliant phone has wrongly classified a CDP port as a DCP port and

has not made a data connection



The PI5USB2546 will then automatically do a OUT (VBUS) discharge and reconfigure the port as an SDP



This allows the phone to discover it is now connected to an SDP and establish a data connection



The PI5USB2546 will then switch automatically back to CDP without doing an OUT (VBUS) discharge



The phone will continue to operate like it is connected to a SDP since OUT (VBUS) was not interrupted



The port is now ready in CDP if a new device is attached

Over-Current Protection

When an over-current condition is detected, the device maintains a constant output current and reduces the output voltage

accordingly. Two possible overload conditions can occur. In the first condition, the output has been shorted before the device is

enabled or before VIN has been applied. The PI5USB2546 senses the short and immediately switches into a constant-current

output. In the second condition, a short or an overload occurs while the device is enabled. At the instant the overload occurs,

high currents may flow for nominally one to two microseconds before the current-limit circuit can react. The device operates in

constant-current mode after the current-limit circuit has responded. Complete shutdown occurs only if the fault is presented

long enough to activate thermal limiting. The device will remain off until the junction temperature cools approximately 20°C

and will then re-start. The device will continue to cycle on/off until the over-current condition is removed.