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

2015-08-0011

PT0497-4

08/31/15

9

PI5PD2556/2557

Precision Adjustable

Current-Limited Power Switch

Application Information

Input and Output Capacitance

Input and output capacitance improves the performance of the device; the actual capacitance should be optimized for the particular

application. For all applications, a 0.1uF or greater ceramic bypass capacitor between IN and GND is recommended as close to the

device as possible for local noise decoupling. This precaution reduces ringing on the input due to power-supply transients.

Additional input capacitance may be needed on the input to reduce voltage overshoot from exceeding the absolute-maximum

voltage of the device during heavy transient conditions or output shorting. This is especially important during bench testing when

long inductive cables are used to connect the evaluation board to the bench power supply. Normally suggested the distance

between IC and DC supply source is less than 15cm.

Output capacitance also need to be close to IC as possible. When large transient currents are expected on the output , placing a

high-value electrolytic capacitor on the output pin is recommended.

Programming the Current-Limit Threshold

The overcurrent threshold is user programmable via an external resistor. The PI5PD2556/57 uses an internal regulation loop to

provide a regulated voltage on the ILIM pin. The current-limit threshold is proportional to the current sourced out of ILIM. The

recommended 1% resistor range for RILIM is 20 kΩ ≤ RILIM ≤ 187 kΩ to ensure stability of the internal regulation loop.

Many applications require that the minimum current limit is above a certain current level or that the maximum current limit is

below a certain current level, so it is important to consider the tolerance of the overcurrent threshold when selecting a value for

RILIM. The following equations approximate the resulting overcurrent threshold for a given external resistor value ®ILIM).

Consult the Electrical Characteristics table for specific current limit settings. The traces routing the RILIM resistor to the

PI5PD2556/57 should be as short as possible to reduce parasitic effects on the current-limit accuracy.

Figure 16 Current Limit Threshold & RILIM

Application 1: Designing above a Minimum Current Limit

Some applications require that current limiting cannot occur below a certain threshold. For this example, assume

that 3 A must be delivered to the load so that the minimum desired current-limit threshold is 3000 mA. Use the