PI5USB2546J

www.diodes.com

November 2020

Document Number DS43167 Rev 1-2

26

© Diodes Incorporated

PI5USB2546J

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 PI5USB2546J 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.

Current-Limit Settings

The PI5USB2546J has two independent current limit settings that are each programmed externally with a resistor. The ILIM_HI

setting is programmed with RILIM_HI connected between ILIM_HI and GND. The ILIM_LO setting is programmed with RILIM_LO

connected between ILIM_LO and GND. Consult the Device Truth Table to see when each current limit is used. Both settings

have the same relation between the current limit and the programming resistor. RILIM_LO is optional and the ILIM_LO pin may

be left unconnected if the following conditions are met:

1.

ILIM_SEL is always set high

2.

Load Detection - Port Power Management is not used

The following equation programs the typical current limit:

IOS_TYP (mA)=50250/RLIM_xx (kΩ)

RILIM_XX corresponds to either RILIM_HI or RILIM_LO as appropriate.

Many applications require that the current limit meet specific tolerance limits. When designing to these tolerance limits, both

the tolerance of the PI5USB2546J current limit and the tolerance of the external programming resistor must be taken into

account. The following equations approximate the PI5USB2546J minimum / maximum current limits to within a few mA and

are appropriate for design purposes. These equations assume an ideal – no variation - external programming resistor. To take

resistor tolerance into account, first determine the minimum /maximum resistor values based on its tolerance specifications and

use these values in the equations. Because of the inverse relation between the current limit and the programming resistor, use

the maximum resistor value in the IOS_MIN equation and the minimum resistor value in the IOS_MAX equation.

IOS_MIN (mA)=45271/(RLIM_xx (kΩ))0.98437-30

IOS_MAX (mA) =55325/ (RLIM_xx (kΩ)) 1.0139+30

The traces routing the RILIM_XX resistors should be a sufficiently low resistance as to not affect the current-limit accuracy. The

ground connection for the RILIM_XX resistors is also very important. The resistors need to reference back to the PI5USB2546J

GND pin. Follow normal board layout practices to ensure that current flow from other parts of the board does not impact the

ground potential between the resistors and the PI5USB2546J GND pin.

/FAULT Response

The /FAULT open-drain output is asserted (active low) when an over-temperature or current limit condition occurs.

The PI5USB2546J is designed to eliminate false /FAULT reporting by using an internal deglitch circuit for current limit

conditions without the need for external circuitry. This ensures that /FAULT is not accidentally asserted due to normal

operation such as starting into a heavy capacitive load. Over-temperature conditions are not deglitched and assert the /FAULT

signal immediately.