1
Rev. 0
DESCRIPTION
LTC3311S
3.3V to 1.2V at 12.5A, 2MHz Low EMI Buck
Regulator in a 1.17cm
2
Solution
Demonstration Circuit 3018A features the
12.5A, low voltage, synchronous step-down Silent
Switcher
®
2 operating as a 2MHz 3.3V to 1.2V 12.5A buck
regulator. The LTC3311S supports output voltages from
0.5V to V
IN
with operating frequencies from 500kHz up
to 5MHz. The LTC3311S is a compact, ultralow emission,
high efficiency, and high speed synchronous monolithic
step-down switching regulator. The integrated bypass
capacitors optimize all the fast current loops and make it
easier to minimize EMI/EMC emissions by reducing layout
sensitivity. Fast minimum on-time of 35ns enables high
V
IN
to low V
OUT
conversion at high frequency.
DC3018A is set up to run in forced continuous mode with
a 2MHz switching frequency but can be configured to
pulse skip mode or different switching frequencies. RT is
connected to VIN which sets the MODE/SYNC pin as an
input and allows the LTC3311S to sync from an external
clock. Connecting the MODE/SYNC pin to VIN sets the
mode to pulse skip mode and connecting the MODE/SYNC
pin to GND sets the mode to forced continuous mode.
The Efficiency vs Load graph shows the efficiency and
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PERFORMANCE SUMMARY
the power loss of the circuit with a 3.3V input in forced
continuous mode operation.
The DC3018A also has an EMI filter to reduce conducted
EMI. This EMI filter can be included by applying the input
voltage at the VIN EMI terminal. The EMI performance
of the board is shown in the EMI Test Results section.
The red lines in the EMI performance graphs illustrate
the CISPR25 Class 5 peak limits for the conducted and
radiated emission tests.
The LTC3311S data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this demo. The
LTC3311S is assembled in a 3mm × 3mm LQFN package
with exposed pads for low thermal resistance. The layout
recommendations for low EMI operation and maximum
thermal performance are available in the data sheet sec-
tion Low EMI PCB Layout.
Design files for this circuit board are available
Specifications are at T
A
= 25°C
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Voltage Range
2.25
5.5
V
V
OUT
Voltage Range*
1.176
1.2
1.224
V
OUTPUT Current
V
IN
> 3V
12.5
A
Switching Frequency
1.8
2.2
MHz
Minimum On-Time
35
60
ns
*With 1% feedback resistors. Accuracy will improve to within 1% using 0.1% FB resistors.
