Protection IC Datasheet

© 2022 Littelfuse, Inc.

Specifications are subject to change without notice.

Revised: FW.12/01/22

LS0504EDD12

5.5V 4A Low-Ron Power Distribution Load Switch

PD(MAX) =

TJMAX −TA

=

RθJA

135°C − 25°C

200°C

=0. 55W

Thermal Considerations

For best performance, all traces should be as short as possible. To be most effective, the input and output capacitors should be placed

close to the device to minimize the effects that parasitic trace inductances may have on normal and short-circuit operation. Using wide

traces for V

IN, VOUT, and GND helps minimize the parasitic electrical effects along with minimizing the case to ambient thermal impedance.

To ensure reliable operation, assume worst case junction temperature should not exceed +135°C. This restriction limits the power

dissipation the regulator can handle in any given application. To ensure the junction temperature is within acceptable limits, calculate the

maximum allowable dissipation, P

D(max), and the actual dissipation, PD which must be less than or equal to PD(max).

The maximum-power-dissipation limit is determined using the following equation:

Where:

T

J max is the maximum allowable junction temperature.

Rθ

JA is the thermal resistance junction-to-ambient for the package (see the Dissipation Ratings table).

T

A is the ambient temperature.

PCB Layout Recommendation

1. IN and OUT traces should be as short and wide as possible to accommodate for high current.

2. The IN pin should be bypassed to ground with low ESR ceramic bypass capacitors. The typical recommended bypass capacitance is

10μF ceramic with X5R or X7R dielectric. This capacitor should be placed as close to the device pins as possible.

3. The OUT pin should be bypassed to ground with low ESR ceramic bypass capacitors. The typical recommended bypass capacitance is

one-tenth of the VIN bypass capacitor of X5R or X7R dielectric rating. This capacitor should be placed as close to the device pins as

possible.

Application Information

The LS0504EDD12 is a load switch that integrates an internal low Ron N-channel MOSFET to reduce power loss. It operates with wide

input voltage range and provides comprehensive protections.

Input and Output Capacitor Selection

For stable operation, recommend to place a 10μF or higher ceramic type X5R or X7R bypass capacitor at the IN and OUT pins. When the

input is connected to a USB port, either USB cable hot plug-in or output short circuit can cause large ringing on the input. The device inter-

nal circuitry could be damaged if the input ringing voltage exceeds the absolute maximum rating of 6V. For these applications, it’s recom-

mend to add a 220µF or greater Aluminum bypass capacitor or 6V rating Transient Voltage Suppressor (TVS) at the input to absorb large

input surge current.

Enable

When input voltage is above the internal input under-voltage lockout threshold (typ.1.65V), the LS0504EDD12 can be enabled by pulling

the EN pin to above 1.2V. The device is disabled if the EN pin is pulled below 1.1V. The enable/disable threshold for EN pin is accurately

designed to be 1.2V and 1.1V respectively, so one can also use external resistor divider to program the external input under-voltage lockout

level (above 1.65V). Pull EN pin below 0.4V to turn off all circuitry and get <1µA shutdown current.

Soft-Start

The LS0504EDD12 has built-in 250µs soft start at enable. During the soft start period, VOUT will ramp up with a controlled slew rate to

minimize input inrush current.

Theory of Operation

The LS0504EDD12 is 5.5V low R

ON current limited load switches in 4-pin DFN1.2mmx 1.6mm package. To minimize voltage drop for low

voltage and high current rails, the device integrates an ultra-low R

ON N-channel MOSFET switch with 26mΩ. At enable, the LS0504E has

internal soft-start which reduces inrush current and minimizes input power supply droop. When disabled, the device automatically

discharges output voltage through an internal 8 Ω resistor. The LS0504EDD12 comes with built-in over current, over voltage and over

temperature fault protection. When over current condition is detected, the LS0504EDD12 enters hiccup mode to minimize power

dissipations. In hiccup mode, the power MOSFET is turned off to disconnect the load from input supply for a pre-determined period of

time before it automatically re-tries to start up again with soft-start. If the over load condition persists with high ambient temperature,

LS0504EDD12 junction temperature could rise above +140 ˚C. which is the built-in over temperature protection threshold. In this case, the

LS0504EDD12 will turn off the power switch and wait for the junction temperature to drop below +95˚C before it tries to automatically

re-start.