Datasheet LTC3448 (Analog Devices) - 7
| Hersteller | Analog Devices |
| Beschreibung | 1.5MHz/2.25MHz, 600mA Synchronous Step-Down Regulator with LDO Mode |
| Seiten / Seite | 20 / 7 — FU CTIO AL DIAGRA. Figure 1. OPERATIO (Refer to Functional Diagram). Main … |
| Dateiformat / Größe | PDF / 284 Kb |
| Dokumentensprache | Englisch |
FU CTIO AL DIAGRA. Figure 1. OPERATIO (Refer to Functional Diagram). Main Control Loop. Pulse Skipping Mode Operation
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LTC3448
U U W FU CTIO AL DIAGRA
SYNC MODE 7 3 FREQ SLOPE LDO CONTROL 6 COMP LOGIC VIN OSC VOUT LDO 2 4 V DRIVE IN – + + 0.6V – + 5Ω VFB I – EA COMP 1 OSC S Q R Q VIN SWITCHING RS LATCH LOGIC AND ANTI- RUN BLANKING SHOOT- 8 0.6V REF – CIRCUIT THRU 5 SW OVDET 0.6V + ∆OVL + + SHUTDOWN IRCMP– 9 GND 3448 F01
Figure 1 U OPERATIO (Refer to Functional Diagram) Main Control Loop
comparator OVDET guards against transient overshoots The LTC3448 uses a constant frequency, current mode, 5.8% by turning off the main switch and keeping it off until step-down architecture. Both the main (P-channel MOS- the fault is removed. FET) and synchronous (N-channel MOSFET) switches are
Pulse Skipping Mode Operation
internal. During normal operation, the internal top power MOSFET is turned on each cycle when the oscillator sets At light loads, the inductor current may reach zero or the RS latch, and turned off when the current comparator, reverse on each pulse. The bottom MOSFET is turned off I by the current reversal comparator, I COMP, resets the RS latch. The peak inductor current at RCMP, and the switch which I voltage will ring. This is discontinuous mode operation, COMP resets the RS latch, is controlled by the output of error amplifier EA. When the load current and is normal behavior for the switching regulator. At very increases, it causes a slight decrease in the feedback light loads, the LTC3448 will automatically skip pulses to voltage FB maintain output regulation. INT relative to the 0.6V reference, which in turn, causes the EA amplifier’s output voltage to increase until the average inductor current matches the new load cur-
Low Ripple LDO Mode Operation
rent. While the top MOSFET is off, the bottom MOSFET is At load currents below ILDO(ON), and when enabled, the turned on until either the inductor current starts to re- LTC3448 will switch into very low ripple, linear regulating verse, as indicated by the current reversal comparator operation (LRO). In this mode, the current is sourced from IRCMP, or the beginning of the next clock cycle. The 3448f 7
U U W FU CTIO AL DIAGRA
SYNC MODE 7 3 FREQ SLOPE LDO CONTROL 6 COMP LOGIC VIN OSC VOUT LDO 2 4 V DRIVE IN – + + 0.6V – + 5Ω VFB I – EA COMP 1 OSC S Q R Q VIN SWITCHING RS LATCH LOGIC AND ANTI- RUN BLANKING SHOOT- 8 0.6V REF – CIRCUIT THRU 5 SW OVDET 0.6V + ∆OVL + + SHUTDOWN IRCMP– 9 GND 3448 F01
Figure 1 U OPERATIO (Refer to Functional Diagram) Main Control Loop
comparator OVDET guards against transient overshoots The LTC3448 uses a constant frequency, current mode, 5.8% by turning off the main switch and keeping it off until step-down architecture. Both the main (P-channel MOS- the fault is removed. FET) and synchronous (N-channel MOSFET) switches are
Pulse Skipping Mode Operation
internal. During normal operation, the internal top power MOSFET is turned on each cycle when the oscillator sets At light loads, the inductor current may reach zero or the RS latch, and turned off when the current comparator, reverse on each pulse. The bottom MOSFET is turned off I by the current reversal comparator, I COMP, resets the RS latch. The peak inductor current at RCMP, and the switch which I voltage will ring. This is discontinuous mode operation, COMP resets the RS latch, is controlled by the output of error amplifier EA. When the load current and is normal behavior for the switching regulator. At very increases, it causes a slight decrease in the feedback light loads, the LTC3448 will automatically skip pulses to voltage FB maintain output regulation. INT relative to the 0.6V reference, which in turn, causes the EA amplifier’s output voltage to increase until the average inductor current matches the new load cur-
Low Ripple LDO Mode Operation
rent. While the top MOSFET is off, the bottom MOSFET is At load currents below ILDO(ON), and when enabled, the turned on until either the inductor current starts to re- LTC3448 will switch into very low ripple, linear regulating verse, as indicated by the current reversal comparator operation (LRO). In this mode, the current is sourced from IRCMP, or the beginning of the next clock cycle. The 3448f 7