LM2585 datasheet(18/32 Pages) TI

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LM2585

SNVS120F – APRIL 2000 – REVISED APRIL 2013

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Step-Up (Boost) Regulator Operation

Figure 45 shows the LM2585 used as a step-up (boost) regulator. This is a switching regulator that produces an

output voltage greater than the input supply voltage.

A brief explanation of how the LM2585 Boost Regulator works is as follows (refer to Figure 45). When the NPN

switch turns on, the inductor current ramps up at the rate of VIN/L, storing energy in the inductor. When the

switch turns off, the lower end of the inductor flies above VIN, discharging its current through diode (D) into the

output capacitor (COUT) at a rate of (VOUT − VIN)/L. Thus, energy stored in the inductor during the switch on time

is transferred to the output during the switch off time. The output voltage is controlled by adjusting the peak

switch current, as described in Flyback Regulator.

Figure 45. 12V Boost Regulator

By adding a small number of external components (as shown in Figure 45), the LM2585 can be used to produce

a regulated output voltage that is greater than the applied input voltage. The switching waveforms observed

during the operation of this circuit are shown in Figure 46. Typical performance of this regulator is shown in

Figure 47.

A: Switch Voltage, 10 V/div

B: Switch Current, 2 A/div

C: Inductor Current, 2 A/div

D: Output Ripple Voltage,

100 mV/div, AC-Coupled

Horizontal: 2

μs/div

Figure 46. Switching Waveforms

Figure 47. VOUT Response to Load Current Step

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