Datasheet

0.0 0.2 0.4 0.6 0.8 1.0 1.2

INPUT VOLTAGE (v)

SHORT CIRCUIT VOLTAGE (v)

SAFE OPERATING AREA

LM22673

www.ti.com

SNVS586N –SEPTEMBER 2008–REVISED APRIL 2013

Where V

is the value of output voltage during the overload and F

is the normal switching frequency. If the

input voltage should exceed this value, while in foldback mode, the regulator and/or the diode may be

damaged. It is important to note that the voltages in these equations are measured at the inductor. Normal trace

and wiring resistance will cause the voltage at the inductor to be higher than that at a remote load. Therefore,

even if the load is shorted with zero volts across its terminals, the inductor will still see a finite voltage. It is this

value that should be used for V

and V

in the calculations. In order to return from foldback mode, the load must

be reduced to a value much lower than that required to initiate foldback. This load "hysteresis" is a normal aspect

of any type of current limit foldback associated with voltage regulators.

The safe operating area, when in short circuit mode, is shown in Figure 13. Operating points below and to the

right of the curve represent safe operation.

Figure 13. SOA

Current Limit Adjustment

A key feature of the LM22673 is the ability to adjust the peak switch current limit. This can be useful when the full

current capability of the regulator is not required for a given application. A smaller current limit may allow the use

of power components with lower current ratings, thus saving space and reducing cost. A single resistor between

the IADJ pin and ground controls the current limit in accordance with Figure 14. The current limit mode is set

during start-up of the regulator. When V

is applied, a weak pull-up is connected to the IADJ pin and, after

approximately 100 µs, the voltage on the pin is checked against a threshold of about 0.8V. With the IADJ pin

open, the voltage floats above this threshold, and the current limit is set to the default value of 4.2A (typ). With a

resistor present, an internal reference holds the pin voltage at 0.8V; the resulting current sets the current limit.

The accuracy of the adjusted current limit will be slightly worse than that of the default value; +35%/ -25% is to

be expected. Resistor values should not exceed the limits shown in Figure 14

Figure 14. Current Limit vs IADJ Resistor

Product Folder Links: LM22673