QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1171A
SYNCHRONOUS BUCK CONVERTER
1
LTC3851EGN
DESCRIPTION
Demonstration circuit 1171A is a single output
synchronous buck converter featuring the
LTC3851EGN. The circuit is designed with all
components on the top side. The package style for
the LTC3851EGN is a 16-lead narrow SSOP.
Two versions of the board are available. DC-
1171A-A has an on-board sense resistor for cur-
rent feedback, while the DC1171A-B is configured
with a DCR sense circuit that allows the converter
to use the inductor’s DCR as the sense element
instead of the on-board sense resistor to save
cost, board space while improving full load effi-
ciency over 2%.
The main features of the board include an internal
5V linear regulator for bias and a Mode selector
that allows the converter to run in CCM, pulse skip
or Burst Mode operation (requires some minor
modification). Synchronization to an external clock
is also possible.
The input voltage range is 4.5V to 14V. The
LTC3851 datasheet gives a complete description
of the part, operation and application information
and must be read in conjunction with this quick
start guide for demo circuit 1171A.
Design files for this circuit board are available.
Call the LTC factory.
Burst Mode is a trademark of Linear Technology Corporation
Table 1. Performance Summary (T
A
= 25°C)
PARAMETER CONDITION VALUE
Input Voltage Range 4.5V - 14V
Output Voltage V
OUT
V
IN
= 4.5V to 14V, I
OUT
= 0A to 15A 1.5V ±2%
Nominal Switching Frequency 400kHz
Efficiency
See Figure 3 and 4 for efficiency curves
V
OUT
= 1.5V, I
OUT1
= 15A; V
IN
= 12V
87.3% Typical (A-A)
90.0% Typical (A-B)
QUICK START PROCEDURE
Demonstration circuit 1171A is easy to set up to
evaluate the performance of the LTC3851EGN.
Refer to Figure 1 for proper measurement equip-
ment setup and follow the procedure below:
NOTE:
When measuring the input or output voltage
ripple, care must be taken to avoid a long ground
lead on the oscilloscope probe. Measure the input
or output voltage ripple by touching the probe tip
directly across the Vin or Vout and GND terminals.
See Figure 2 for proper scope probe technique.
1.
Place jumpers in the following positions:
400k
On
CCM
2.
With power off, connect the input power supply
to Vin and GND.
3.
Turn on the power at the input.
NOTE:
Make sure that the input voltage does not
exceed 14V.
