Analog Devices DC2745A Demo Manual

DESCRIPTION
Demonstration Circuit 2745A features the
6A synchronous step-down silent switcher operating as
a 2MHz, 3.3V to 1.2V 6A buck regulator. The LTC3309A
supports adjustable output voltages from 0.5V to V
and operating frequencies from 1MHz up to 3MHz. The
LTC3309A is a compact, ultralow emission, high effi-
ciency, and high speed synchronous monolithic step-
down switching regulator. A minimum on-time of 22ns
enables high V to low V
IN
switching frequencies.
The DC2745A operating mode may be selected as
Burst Mode operation, skip or forced continuous (FC)
®
mode. Setting JP1 to the FC/SYNC position will allow
the LTC3309A to sync to a clock frequency from 1MHz
to 3MHz. The LTC3309A operates in forced continuous
mode when syncing to an external clock.
The DC2745A is set to a fixed 2MHz frequency by con-
necting RT to V through a 0Ω resistor, R9. The frequency
IN
can be easily changed by removing R9 and setting an
appropriate resistor in the R4 location to obtain the
desired frequency. Refer to the LTC3309A data sheet for
the proper RT value for a desired switching frequency.
PERFORMANCE SUMMARY
SYMBOL PARAMETER
V Input Voltage Range
IN
V V Voltage Range*
OUT OUT
I OUTPUT Current
OUT
f Switching Frequency
SW
t Top Switch Minimum On Time
ON
Duty Cycle Top Switch Duty Cycle
*With 1% resistors. Accuracy will improve to within 1% using 0.1% FB resistors.
5V, 6A Synchronous Step-Down
Silent Switcher in 2mm × 2mm LQFN
LTC 3309A
®
conversion ratios at high
OUT
Specifications are at T
CONDITIONS
V
IN
DEMO MANUAL DC2745A
5V, The DC2745A also has an EMI filter to reduce conducted
EMI. This EMI filter can be included by applying the input
voltage at the V
IN
, the board is shown in the EMI Test Results section. The
IN
red lines in the EMI performance graphs illustrate the
CISPR25 Class 5 peak limits for the conducted and radi-
ated emission tests.
The LTC3309A 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 LTC3309A is assembled in a 2mm × 2mm
LQFN package with exposed pads for low thermal resis-
tance. The layout recommendations for low EMI operation
and maximum thermal performance are available in the
data sheet section Low EMI 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.
Design files for this circuit board are
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= 25°C
A
Greater than V
OUT
LTC3309A
EMI terminal. The EMI performance of
available.
MIN TYP MAX
2.25
1.183 1.2 1.217
1
22
100
UNITS
5.5 V
V
6 A
3 MHz
ns
%
Rev. 0
1