DESCRIPTION
Demonstration circuit 3122A features the LTC®3307A
5V, 3A synchronous step-down Silent Switcher® operating
as a 2MHz, 3.3V to 1.2V 3A buck regulator. The
LTC3307A supports adjustable output voltages from
0.5V to VIN with operating frequencies from 1MHz up to
3MHz. The LTC3307A is a compact, ultralow emission,
high efficiency, and high speed synchronous monolithic
step-down switching regulator. A minimum on-time of
22ns enables high VIN to low VOUT conversion ratios at
high frequencies.
The DC3122A operating mode may be selected as Burst,
Skip or forced continuous (FC) mode. Setting JP1 to the
FC/SYNC position will allow the LTC3307A to sync to a
clock frequency from 1MHz to 3MHz. The LTC3307A
operates in forced continuous mode when syncing to
an external clock. The DC3122A is set to a fixed 2MHz
frequency by connecting RT to VIN through a 0Ω resistor,
R9. The frequency can be easily changed by removing
R9 and setting an appropriate resistor in the R4 location
to obtain the desired frequency. Refer to the LTC3307A
data sheet for the proper RT value for a desired switching
frequency.
The DC3122A also has an Electromagnetic interference
(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 LTC3307A data sheet gives a complete description of
the device, operation and application information. The data
sheet must be read in conjunction with this demo manual.
The LTC3307A is assembled in a 1.6mm × 1.6mm Wafer
Level Chip Scale Package (WLCSP) with exposed pads for
low thermal resistance. The layout recommendations for
low EMI operation and maximum thermal performance
are available in the data sheet section Low EMI Printed
Circuit Board (PCB) Layout.
The Efficiency vs Load graph shows the efficiency and
the power loss of the circuit with a 3.3V input in Burst
Mode® operation.