Analog Devices LTC3308A Demo Manual

DESCRIPTION
Demonstration circuit 2991A features the
5V, 4A synchronous step-down Silent Switcher
ating as a 2.0MHz, 3.3V to 1.2V 4A buck regulator. The
LTC3308A supports adjustable output voltages from 0.5V
to V with operating frequencies from 1MHz up to 3MHz.
IN
The LTC3308A is a compact, ultralow emission, high
efficiency, and high speed synchronous monolithic step-
down switching regulator. A minimum on-time switching
of 22ns enables high V
IN
at high frequencies.
The DC2991A operating mode may be selected as BURST,
SKIP or Forced Continuous (FC) mode. Setting JP1 to
the FC/SYNC position will allow the LTC3308A to sync to
a clock frequency from 1MHz to 3MHz. The LTC3308A
operates in forced continuous mode when syncing to an
external clock. The DC2991A 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 LTC3308A 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 4A Synchronous
Step‑Down Silent Switcher Demo Circuit
LTC 3308A
®
®
to low V conversion ratios
OUT
through a 0Ω resistor, R9.
IN
Specifications are at T
CONDITIONS
V
IN
DEMO MANUAL DC2991A
The DC2991A also has an EMI filter to reduce conducted
oper- EMI. This EMI filter can be included by applying the input
voltage at the V
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 LTC3308A 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 LTC3308A 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
LTC3308A
EMI terminal. The EMI performance of
IN
available.
MIN TYP
2.25
1.183 1.2
1
22
MAX UNITS
5.5 V
1.217 V
4 A
3 MHz
ns
100 %
Rev. 0
1