|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||

|||||||||||||||||

2015-08-0009

PT0514-4

08/24/15

20

PI5USB2544

USB Charging Port Controller and Detection Power Switch

Current-Limit Settings

The PI5USB2544 have two independent current limit settings that are each programmed externally with a resistor. The

ILIM_LO pin may be left unconnected if the ILIM_SEL is always set high.

The following equation programs the typical current limit:

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 PI5USB2544 current limit and the tolerance of the external programming resistor must be taken into

account. The following equations approximate the PI5USB2544 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

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 PI5USB2544 GND pin.

/FAULT Response

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

remains asserted until the fault condition is removed. The PI5USB2544 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.

Undervoltage Lockout (UVLO)

The undervoltage lockout (UVLO) circuit disables the power switch until the input voltage reaches the UVLO turn on threshold.

Built-in hysteresis prevents unwanted oscillations on the output due to input voltage drop from large current surges.

Thermal Sense

The PI5USB2544 protects itself with thermal sensing circuit that monitor the operating temperature of the power distribution

switch and disables operation if the temperature exceeds recommended operating conditions. The device operates in constant-

current mode during an over-current condition, which increases the voltage drop across power switch. The power dissipation in

the package is proportional to the voltage drop across the power switch, so the junction temperature rises during an over-current

condition. The thermal sensor turns off the power switch when the die temperature exceeds 170°C regardless of whether the

power switch is in current limit. Hysteresis is built into thermal sensor, and the switch turns on after the device has cooled by

approximately 20°C. The switch continues to cycle off and on until the fault is removed. The open-drain false reporting output

/FAULT is asserted (active low) when an over-temperature shutdown condition.