Datasheet LTC3409 (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | 600mA Low VIN Buck Regulator in 3mm × 3mm DFN |
| Pages / Page | 16 / 8 — FUNCTIONAL DIAGRAM. OPERATION. Main Control Loop. Burst Mode Operation |
| File Format / Size | PDF / 295 Kb |
| Document Language | English |
FUNCTIONAL DIAGRAM. OPERATION. Main Control Loop. Burst Mode Operation
Model Line for this Datasheet
Text Version of Document
LTC3409
FUNCTIONAL DIAGRAM
MODE 5 SLOPE SYNC COMP 0.65V 8 PLL OSC VIN – 3, 4 VFB EN + – 1 SLEEP + 0.613V 5Ω – 0.4V + – + I EA COMP BURST S Q SOFT- R Q START SWITCHING RS LATCH LOGIC VIN AND ANTI- BLANKING SHOOT- CIRCUIT THRU 6 SW RUN + 7 REFERENCE OV OVDET 0.675 – + SHUTDOWN IRCMP– 2 GND 3409 FD
OPERATION Main Control Loop
by the current reversal comparator IRCMP, or the beginning The LTC3409 uses a constant frequency, current mode step- of the next clock cycle. down architecture. Both the main (P-channel MOSFET) and Comparator OVDET guards against transient overshoots synchronous (N-channel MOSFET) switches are internal. >10% by turning the main switch off and keeping it off During normal operation, the internal top power MOSFET until the transient has ended. is turned on each cycle when the oscillator sets the RS latch, and turned off when the current comparator, ICOMP,
Burst Mode Operation
resets the RS latch. The peak inductor current at which The LTC3409 is capable of Burst Mode operation in which ICOMP resets the RS latch is controlled by the output of error the internal power MOSFETs operate intermittently based amplifi er EA. The VFB pin, described in the Pin Functions on load demand. To enable Burst Mode operation, simply section, allows EA to receive an output feedback voltage connect the MODE pin to GND. To disable Burst Mode from an external resistive divider. When the load current operation and enable PWM pulse skipping mode, connect increases, it causes a slight decrease in the feedback voltage the MODE pin to V relative to the 0.613V reference, which in turn, causes the IN or drive it with a logic high (VMODE >1.1V). In this mode, the effi ciency is lower at light loads, EA amplifi er’s output voltage to increase until the average but becomes comparable to Burst Mode operation when inductor current matches the new load current. While the the output load exceeds 30mA. The advantage of pulse top MOSFET is off, the bottom MOSFET is turned on until skipping mode is lower output ripple and less interference either the inductor current starts to reverse, as indicated 3409fc 8
FUNCTIONAL DIAGRAM
MODE 5 SLOPE SYNC COMP 0.65V 8 PLL OSC VIN – 3, 4 VFB EN + – 1 SLEEP + 0.613V 5Ω – 0.4V + – + I EA COMP BURST S Q SOFT- R Q START SWITCHING RS LATCH LOGIC VIN AND ANTI- BLANKING SHOOT- CIRCUIT THRU 6 SW RUN + 7 REFERENCE OV OVDET 0.675 – + SHUTDOWN IRCMP– 2 GND 3409 FD
OPERATION Main Control Loop
by the current reversal comparator IRCMP, or the beginning The LTC3409 uses a constant frequency, current mode step- of the next clock cycle. down architecture. Both the main (P-channel MOSFET) and Comparator OVDET guards against transient overshoots synchronous (N-channel MOSFET) switches are internal. >10% by turning the main switch off and keeping it off During normal operation, the internal top power MOSFET until the transient has ended. is turned on each cycle when the oscillator sets the RS latch, and turned off when the current comparator, ICOMP,
Burst Mode Operation
resets the RS latch. The peak inductor current at which The LTC3409 is capable of Burst Mode operation in which ICOMP resets the RS latch is controlled by the output of error the internal power MOSFETs operate intermittently based amplifi er EA. The VFB pin, described in the Pin Functions on load demand. To enable Burst Mode operation, simply section, allows EA to receive an output feedback voltage connect the MODE pin to GND. To disable Burst Mode from an external resistive divider. When the load current operation and enable PWM pulse skipping mode, connect increases, it causes a slight decrease in the feedback voltage the MODE pin to V relative to the 0.613V reference, which in turn, causes the IN or drive it with a logic high (VMODE >1.1V). In this mode, the effi ciency is lower at light loads, EA amplifi er’s output voltage to increase until the average but becomes comparable to Burst Mode operation when inductor current matches the new load current. While the the output load exceeds 30mA. The advantage of pulse top MOSFET is off, the bottom MOSFET is turned on until skipping mode is lower output ripple and less interference either the inductor current starts to reverse, as indicated 3409fc 8
