LM2614ATLX NSC [National Semiconductor], LM2614ATLX Datasheet - Page 9

• Manufacturer Part Number: LM2614ATLX
• Description: 400mA Sub-Miniature Adjustable DC-DC Converter Optimized for RF Power Amplifiers
• Manufacturer: NSC [National Semiconductor]

Device Information
CIRCUIT OPERATION
Referring to Figure 4, Figure 5, Figure 6 and Figure 7,
the LM2614 operates as follows. During the first part of each
switching cycle, the control block in the LM2614 turns on the
internal PFET switch. This allows current to flow from the
input through the inductor to the output filter capacitor and
load. The inductor limits the current to a ramp with a slope of
(V
the second part of each cycle, the controller turns the PFET
switch off, blocking current flow from the input, and then
turns the NFET synchronous rectifier on. In response, the
inductor’s magnetic field collapses, generating a voltage that
forces current from ground through the synchronous rectifier
to the output filter capacitor and load. As the stored energy is
IN
–V
OUT
)/L, by storing energy in a magnetic field. During
(Continued)
FIGURE 5. Simplified Functional Diagram
FIGURE 4. Typical Operating Circuit
9
transferred back into the circuit and depleted, the inductor
current ramps down with a slope of V
current reaches zero before the next cycle, the synchronous
rectifier is turned off to prevent current reversal. The output
filter capacitor stores charge when the inductor current is
high, and releases it when low, smoothing the voltage across
the load.
The output voltage is regulated by modulating the PFET
switch on time to control the average current sent to the load.
The effect is identical to sending a duty-cycle modulated
rectangular wave formed by the switch and synchronous
rectifier at SW to a low-pass filter formed by the inductor and
output filter capacitor. The output voltage is equal to the
average voltage at the SW pin.
OUT
20036706
20036707
/L. If the inductor
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