LTC3615-1_15 Datasheet, PDF (13/32 Pages) Linear Technology – Dual 4MHz, 3A Synchronous Step-Down DC/DC Converter

LTC3615/LTC3615-1
Operation
Burst Mode Operation—External Clamp
Connecting the MODE pin to a voltage in the range of 0.5V
to 0.8V enables Burst Mode operation with external clamp.
During this mode of operation, the minimum voltage on
the ITH pin is externally set by the voltage on the MODE
pin. It is recommended to use Burst Mode operation with
the internal clamp for ambient temperatures above 85°C.
Pulse-Skipping Mode Operation
Pulse-skipping mode is similar to Burst Mode operation,
but the LTC3615 does not disable power to the internal
circuitry during sleep mode. This improves output voltage
ripple but uses more quiescent current compromising
light load efficiency.
Connecting the MODE pin to SV_IN enables pulse-skipping
mode. As the load current decreases, the peak inductor
current will be determined by the voltage on the ITH pin
until the ITH voltage drops below 450mV, corresponding
to 0A. At this point switching cycles will be skipped to
keep the output voltage in regulation.
Forced Continuous Mode Operation
In forced continuous mode the inductor current is con-
stantly cycled which creates a minimum output voltage
ripple at all output current levels.
Connecting the MODE pin, to a voltage in the range of
1.1V to SV_IN • 0.58 will select the forced continuous mode
operation.
The forced continuous mode must be used if the output
is required to sink current.
Dropout Operation
As the input supply voltage approaches the output voltage,
the duty cycle increases toward the maximum on-time.
Further reduction of the supply voltage forces the main
switch to remain on for more than one cycle, eventually
reaching 100% duty cycle. The output voltage will then be
determined by the input voltage minus the voltage drop
across the internal P-channel MOSFET and the inductor.
LTC3615
V_IN
SV_IN
MODE
0V
SGND
LTC3615
V_IN
SV_IN SW1
MODE FB1
0V
SGND
V_OUT1
R_M1
R_M2
2a. Burst Mode Operation
Internally Controlled
2b. Burst Mode Operation
Externally Controlled
LTC3615
V_IN
SV_IN
MODE
0V
SGND
2c. Pulse-Skipping Mode
LTC3615
V_IN
SV_IN
R_M1
MODE
R_M2
0V
SGND
3615 F02
2d. Forced Continuous Mode
Figure 2. Modes of Operation
For more information www.linear.com/LTC3615
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