MP5087A Rev. 1.0

www.MonolithicPower.com

12

7/18/2014

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APPLICATION INFORMATION

ILIM Resistor Selection

The current limit value can be set by ILIM

resistor. The current limit can be gotten by

equation (1).

The current limit threshold is suggested to 10%

~ 20% higher than maximum load current. For

example, if the system’s full load is 7A, set the

current limit to 7.7A.

ILIM Capacitor Selection

The internal advanced auto-zero comparator

bring a high accuracy of current limit. The auto-

zero will also cause some little jitter on ILIM pin.

To get a more stable ILIM, a small ceramic

capacitor can be mounted between ILIM and

ground. Suggested place a ILIM capacitor less

than 1nF.

Soft Start Capacitor Selection

There is an internal 9µA constant current

source charge SS cap and ramps up the

voltage on the SS pin. The output voltage rises

follow 3 times the slew rate of SS voltage.

If the inrush on output current reached the

current limit during start up (like with large

output cap or very large load), MP5087A will

limit the output current and the same time, SS

time will be increased (Figure 2 and Figure 3).

Soft Start @ Different Load

Soft Start @ No Load

Soft Start @ Half Load

Soft Start @ Very large Load

Current Limit

Current Limit

Current Limit

Figure 2: Soft Start Periods at different load