Datasheet

LM2586
SNVS121D MAY 1996REVISED 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 μA of supply current (16 μA to V
IN
and 40 μA to the ON /OFF pin).
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
R
SET
(k) Frequency (kHz)
Open 100
200 125
47 150
33 175
22 200
Figure 54. Frequency Synchronization
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