Datasheet LTC3406, LTC3406-1.5, LTC3406-1.8 (Analog Devices) - 6
| Hersteller | Analog Devices |
| Beschreibung | 1.5MHz, 600mA Synchronous Step-Down Regulator in ThinSOT |
| Seiten / Seite | 16 / 6 — FU CTIO AL DIAGRA. OPERATIO (Refer to Functional Diagram). Main Control … |
| Dateiformat / Größe | PDF / 247 Kb |
| Dokumentensprache | Englisch |
FU CTIO AL DIAGRA. OPERATIO (Refer to Functional Diagram). Main Control Loop. Burst Mode Operation
Modelllinie für dieses Datenblatt
Textversion des Dokuments
LTC3406 LTC3406-1.5/LTC3406-1.8
U U W FU CTIO AL DIAGRA
SLOPE COMP 0.65V OSC OSC FREQ 4 VIN SHIFT – VFB/VOUT + – 5 SLEEP + 0.6V 5Ω LTC3406-1.5 R1 0.4V + – + I R1 + R2 = 550k FB – EA COMP BURST LTC3406-1.8 S Q R1 + R2 = 540k R2 R Q SWITCHING RS LATCH LOGIC VIN AND ANTI- BLANKING SHOOT- CIRCUIT THRU 3 SW RUN 1 0.6V REF + SHUTDOWN IRCMP– 2 GND 3406 BD
U OPERATIO (Refer to Functional Diagram) Main Control Loop Burst Mode Operation
The LTC3406 uses a constant frequency, current mode The LTC3406 is capable of Burst Mode operation in which step-down architecture. Both the main (P-channel the internal power MOSFETs operate intermittently based MOSFET) and synchronous (N-channel MOSFET) switches on load demand. are internal. During normal operation, the internal top In Burst Mode operation, the peak current of the inductor power MOSFET is turned on each cycle when the oscillator is set to approximately 200mA regardless of the output sets the RS latch, and turned off when the current com- load. Each burst event can last from a few cycles at light parator, ICOMP, resets the RS latch. The peak inductor loads to almost continuously cycling with short sleep current at which ICOMP resets the RS latch, is controlled by intervals at moderate loads. In between these burst events, the output of error amplifier EA. When the load current the power MOSFETs and any unneeded circuitry are turned increases, it causes a slight decrease in the feedback off, reducing the quiescent current to 20µA. In this sleep voltage, FB, relative to the 0.6V reference, which in turn, state, the load current is being supplied solely from the causes the EA amplifier’s output voltage to increase until output capacitor. As the output voltage droops, the EA the average inductor current matches the new load cur- amplifier’s output rises above the sleep threshold signal- rent. While the top MOSFET is off, the bottom MOSFET is ing the BURST comparator to trip and turn the top MOSFET turned on until either the inductor current starts to reverse, on. This process repeats at a rate that is dependent on the as indicated by the current reversal comparator IRCMP, or load demand. the beginning of the next clock cycle. 3406fa 6
U U W FU CTIO AL DIAGRA
SLOPE COMP 0.65V OSC OSC FREQ 4 VIN SHIFT – VFB/VOUT + – 5 SLEEP + 0.6V 5Ω LTC3406-1.5 R1 0.4V + – + I R1 + R2 = 550k FB – EA COMP BURST LTC3406-1.8 S Q R1 + R2 = 540k R2 R Q SWITCHING RS LATCH LOGIC VIN AND ANTI- BLANKING SHOOT- CIRCUIT THRU 3 SW RUN 1 0.6V REF + SHUTDOWN IRCMP– 2 GND 3406 BD
U OPERATIO (Refer to Functional Diagram) Main Control Loop Burst Mode Operation
The LTC3406 uses a constant frequency, current mode The LTC3406 is capable of Burst Mode operation in which step-down architecture. Both the main (P-channel the internal power MOSFETs operate intermittently based MOSFET) and synchronous (N-channel MOSFET) switches on load demand. are internal. During normal operation, the internal top In Burst Mode operation, the peak current of the inductor power MOSFET is turned on each cycle when the oscillator is set to approximately 200mA regardless of the output sets the RS latch, and turned off when the current com- load. Each burst event can last from a few cycles at light parator, ICOMP, resets the RS latch. The peak inductor loads to almost continuously cycling with short sleep current at which ICOMP resets the RS latch, is controlled by intervals at moderate loads. In between these burst events, the output of error amplifier EA. When the load current the power MOSFETs and any unneeded circuitry are turned increases, it causes a slight decrease in the feedback off, reducing the quiescent current to 20µA. In this sleep voltage, FB, relative to the 0.6V reference, which in turn, state, the load current is being supplied solely from the causes the EA amplifier’s output voltage to increase until output capacitor. As the output voltage droops, the EA the average inductor current matches the new load cur- amplifier’s output rises above the sleep threshold signal- rent. While the top MOSFET is off, the bottom MOSFET is ing the BURST comparator to trip and turn the top MOSFET turned on until either the inductor current starts to reverse, on. This process repeats at a rate that is dependent on the as indicated by the current reversal comparator IRCMP, or load demand. the beginning of the next clock cycle. 3406fa 6