LM2586

SNVS121D – MAY 1996 – REVISED APRIL 2013

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APPLICATION HINTS

LM2586 SPECIAL FEATURES

Figure 53. Shutdown Operation

SHUTDOWN CONTROL

A feature of the LM2586 is its ability to be shut down using the ON /OFF pin (pin 1). This feature conserves input

power by turning off the device when it is not in use. For proper operation, an isolation diode is required (as

shown in Figure 53).

The device will shut down when 3V or greater is applied on the ON /OFF pin, sourcing current into pin 1. In shut

down mode, the device will draw typically 56

To turn the device back on, leave pin 1 floating, using an (isolation) diode, as shown in Figure 53 (for normal

operation, do not source or sink current to or from this pin—see the next section).

FREQUENCY ADJUSTMENT

The switching frequency of the LM2586 can be adjusted with the use of an external resistor. This feature allows

the user to optimize the size of the magnetics and the output capacitor(s) by tailoring the operating frequency. A

resistor connected from pin 1 (the Freq. Adj. pin) to ground will set the switching frequency from 100 kHz to 200

kHz (maximum). As shown in Figure 53, the pin can be used to adjust the frequency while still providing the shut

down function. A curve in Typical Performance Characteristics the resistor value to the corresponding switching

frequency. Table 4 shows resistor values corresponding to commonly used frequencies.

However, changing the LM2586's operating frequency from its nominal value of 100 kHz will change the

magnetics selection and compensation component values.

Table 4. Frequency Setting Resistor Guide

Frequency (kHz)

Open

100

200

125

47

150

33

175

22

200

Figure 54. Frequency Synchronization

24

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