Analog Devices DC2990A Manual

DESCRIPTION
Demonstration circuit 2990A features the
5V, 3A synchronous step-down Silent Switcher
ating as a 2MHz, 3.3V to 1.2V 3A buck regulator. The
LTC3307A supports adjustable output voltages from
0.5V to V with operating frequencies from 1MHz up to
IN
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 V to low V
IN
high frequencies.
The DC2990A 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 DC2990A is set to a fixed 2MHz fre-
quency by connecting RT to V
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.
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% resistors.
5V Input to 1.2V Output at 3A Synchronous
Step‑Down Silent Switcher Demo Circuit
LTC 3307A
®
®
conversion ratios at
OUT
through a 0Ω resistor, R9.
IN
Specifications are at T
CONDITIONS
V
IN
DEMO MANUAL DC2990A
The DC2990A also has an EMI filter to reduce conducted
oper- 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
red lines in the EMI performance graphs illustrate the
CISPR25 Class 5 peak limits for the conducted and radi-
ated 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 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
LTC3307A
EMI terminal. The EMI performance of
available.
MIN TYP MAX
2.25
1.183 1.2 1.217
1
22
UNITS
5.5 V
V
3 A
3 MHz
ns
100 %
Rev. 0
1