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DC1787A

P1-P3P4-P6
1
dc1787af
DEMO MANUAL DC1787A
DESCRIPTION
LT3759
Wide Input Voltage Range
Boost/SEPIC/Inverting Controller
Demonstration circuit 1787A is a wide input voltage
range SEPIC converter featuring the LT3759 controller. It
converts a 2.8V~36V input to a 12V output, with 1A load
current capability for V
IN
≥ 4V. The converter operates at
a 300 kHz nominal switching frequency, with 91% peak
efficiency. The DC1787A can be easily modified to gener-
ate other output voltages, and can also be optimized for
efficiency and size with narrower input voltage ranges.
The LT3759 is a boost/SEPIC/Inverting controller with a
wide input voltage range, suitable for applications from
single-cell lithium-ion battery portable electronics to high
voltage automotive and industrial power supplies. It also
exhibits low shutdown quiescent current of 1A, making it
an ideal fit for battery-operated systems. Thanks to a novel
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
PERFORMANCE SUMMARY
FBX pin architecture, the LT3759 can be connected directly
to a divider from either positive output or negative output
voltage to ground. It also packs many popular features
such as soft-start, input undervoltage lockout, adjustable
frequency and synchronization in a small 12-lead exposed
pad MSOP package.
The LT3759 data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this quick start
guide for demo circuit 1787A.
Design files for this circuit board are available at
http://www.linear.com/demo
(T
A
= 25°C)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Voltage Range, V
IN
2.8 12 36 V
Minimum Startup Voltage 3.0 V
Switching Frequency I
OUT
= 0.5A 300 kHz
Output Voltage, V
OUT
V
IN
= 2.8V~36V
I
OUT
= 0mA~0.5A
11.64 12.0 12.36 V
Maximum Continuous Output Current, I
OUT
V
IN
≥ 2.8V 0.5 A
V
IN
≥ 4.0V 1 A
Output Voltage Ripple (Peak-to-Peak) V
IN
= 12V, I
OUT
= 1A 90 mV
Typical Efficiency V
IN
= 12V, I
OUT
= 1A 91 %
2
dc1787af
DEMO MANUAL DC1787A
QUICK START PROCEDURE
Demo circuit 1787A is easy to set up to evaluate the
performance of the LT3759. Refer to Figure 1 for proper
measurement equipment setup and follow the procedure.
1. With power off, connect the input power supply to the
V
IN
(E1) and GND (E2) terminals on the demo circuit.
NOTE: Minimize the voltage drop and transient on the
input wires between the power supply and input terminals
of the demo circuit.
2. Connect load to the V
OUT
(E6) and GND (E5) terminals
on the demo circuit. Connect voltage and current meters
as shown in Figure 1. Preset the load to 0.5A or less,
and V
IN
supply to be 0V.
3. Place jumpers in the following positions for a typical
12V application:
EN (JP1) SYNC (JP2)
ON OFF
NOTE: The demo circuit configures the shutdown voltage
at typical 2.5V, which means that the input voltage can be
dropped to as low as 2.5V, once it starts up. The startup
voltage is 3.0V but can be adjusted by changing R1 and
R3 values.
5. Check for the proper output voltages. The output should
be regulated at 12V (±3%).
NOTE: If there is no output, or output is out of spec, tem-
porarily disconnect the load from the demo board. Make
sure the load current is set within spec, and the power
supply current capability is above 4A.
6. Once the proper output voltage is established, adjust the
input and load within the operating range and observe
the output voltage regulation, ripple voltage, efficiency
and other parameters. Typical efficiency curve, regula-
tion, and operation waveforms are shown in Figures 3
and 4, respectively.
NOTE: When measuring the input or output voltage ripples,
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 V
IN
and GND, or V
OUT
and GND terminals. See Figure 2 for
proper scope probe technique.
4. Turn on the power supply at the input. Slowly increase
V
IN
to 3.0V.
NOTE: Make sure the input voltage is within the range. If
higher operating voltage is required, power components
with higher voltage ratings should be used. The maximum
input voltage of LT3759 is 42V.
NOTE: The output current capability depends on the input
voltage, as can be seen in Figure 3. Proper cooling is
necessary for overload operations.
3
dc1787af
DEMO MANUAL DC1787A
QUICK START PROCEDURE
dc1787af F01
Figure 1. Proper Measurement Equipment Setup
Figure 2. Proper Scope Probe Placement for
Measuring Input or Output Ripple
Figure 3. Efficiency Curves Figure 4. Short Circuit Waveforms with Frequency Foldback
INPUT OR OUTPUT CAPACITOR
dc1787af F02
LOAD CURRENT (mA)
100 300 500 600 700 800200 400 900 1000
dc1787af F03
70
EFFICIENCY (%)
75
80
90
85
95
V
IN
= 12V
V
IN
= 4V
V
IN
= 2.8V
dc1787af F04
V
O
: 10V/DIV
V
DS
: 50V/DIV
I
SW
: 5A/DIV
P1-P3P4-P6

DC1787A

Mfr. #:
Buy DC1787A
Manufacturer:
Analog Devices Inc.
Description:
Power Management IC Development Tools LT3759EMSE SEPIC Demo Board - VIN = 2.8V
Lifecycle:
New from this manufacturer.
Delivery:
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