Datasheet

LM2597, LM2597HV

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SNVS119C –MARCH 1998–REVISED APRIL 2013

NOTE

The lower curve shown in Figure 32 shows the Soft-start region from 0% to 100%. This is

not the duty cycle percentage, but the output voltage percentage. Also, the Soft-start

voltage range has a negative temperature coefficient associated with it. See the Soft-start

curve in Electrical Characteristics.

4. Normal operation. Above 2.8V, the circuit operates as a standard Pulse Width Modulated switching

regulator. The capacitor will continue to charge up until it reaches the internal clamp voltage of approximately

7V. If this pin is driven from a voltage source, the current must be limited to about 1 mA.

If the part is operated with an input voltage at or below the internal soft-start clamp voltage of approximately

7V, the voltage on the SD/SS pin tracks the input voltage and can be disturbed by a step in the voltage. To

maintain proper function under these conditions, it is strongly recommended that the SD/SS pin be clamped

externally between the 3V maximum soft-start threshold and the 4.5V minimum input voltage. Figure 34 is an

example of an external 3.7V (approx.) clamp that prevents a line-step related glitch but does not interfere

with the soft-start behavior of the device.

Figure 32. Soft-start, Delay, Error, Output

Product Folder Links: LM2597 LM2597HV