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DEMO MANUAL DC1687A
Description
LTC3115EDHD-1
40V, 2A Synchronous
Buck-Boost DC/DC Converter
Demonstration circuit 1687A features the LTC
®
3115-1, a
high voltage monolithic synchronous buck-boost converter.
The DC1687A demo board has two user selectable operat-
ing modes: Burst Mode
®
operation and forced continuous
operation (fixed frequency PWM) (JP1). There is also an
accurate programmable RUN pin which is used to enable
the converter (JP2).
The DC1687A operates with a 2.7V to 40V input volt-
age range. The demo board has been designed with the
output voltage set to 5.0V. The LTC3115-1 incorporates a
proprietary low noise switching algorithm which optimizes
efficiency with input voltages above, below or equal to the
output voltage and ensures seamless transitions between
operating modes.
The demo board has been programmed to operate at 1MHz
in PWM mode to optimize small size with high efficiency
operation.
L, LT, LTC, LTM, µModule, Burst Mode, 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
The demo board also has optional provisions to back
feed V
CC
in order to increase efficiency in some 5V out-
put applications. There is also a provision for an optional
Schottky diode from SW2 to V
OUT
for applications where
V
OUT
is greater than 20V and short circuit protection is
desired. Consult the data sheet for more information on
these options.
Figures 1 and 2 show typical demo board efficiency.
The LTC3115-1 data sheet has detailed information about
the operation, specifications, and applications of the part.
The data sheet should be read in conjunction with this
quick start guide.
Design files for this circuit board are available at
http://www.linear.com/demo
PARAMETER VALUE
Input Voltage Range 2.7V to 40V
V
OUT
5.0V
I
OUT
(See Note 1) 1A For V
IN
≥ 3.6V,
2A For V
IN
> 6V
Efficiency See Figures 1 and 2
Note 1: The Demo Board output current is a function of V
IN
. Please refer to the data sheet for more information
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DEMO MANUAL DC1687A
Quick start proceDure
Using short twisted pair leads for any power connections
and with all loads and power supplies off, refer to Figure 3
for the proper measurement and equipment setup. The
battery/power supply (PS1) should not be connected to
the circuit until told to do so in the procedure below.
When measuring the input or output voltage ripple, care
must be taken to avoid a long ground lead on the oscil-
loscope probe. Measure the input or output voltage ripple
by touching the probe tip directly across the V
IN
or V
OUT
and GND terminals (see Figure 4), or by using an oscil-
loscope probe tip jack.
1. Jumper and PS1 settings to start:
PS1 = OFF
JP1 (PWM) = fixed frequency
JP2 (RUN) = ON
2. With power OFF connect the power supply (PS1) as
shown in Figure 3. If accurate current measurements
are desired (for efficiency calculation for example) then
connect an ammeter in series with the supply as shown.
The ammeter is not required however.
3. Connect a 500mA load to V
OUT
as shown in Figure 3
(10Ω for V
OUT
= 5V). Connect an ammeter if accurate
current measurement or monitoring is desired.
4. Turn on PS1 and slowly increase voltage until the volt-
age at V
IN
is 4.0V.
5. Verify V
OUT
is ~5.0V.
6. V
IN
can now be varied between 2.7V and 40.0V. I
OUT
may
need to be reduced for V
IN
< 4V. V
OUT
should remain in
regulation.
7. Load current (I
OUT
) can also be varied. The maximum
I
OUT
is a function of V
IN
and the current limit. Consult
the data sheet for more information on I
OUT
vs V
IN
. In
general for V
IN
> 3.6V I
OUT
can be increased to 1A. For
V
IN
> 6V I
OUT
can be increased to 2A.
8. For operation in Burst Mode operation move Jumper
JP1 to burst. I
OUT
is limited in Burst Mode operation.
See the data sheet for more information.
9. NOTE: If V
OUT
drops out of regulation, check to be sure
the maximum load has not been exceeded, or that V
IN
is not below the minimum value for regulation (see data
sheet)
0
100
90
80
70
60
50
5 10 15 20 25 30 35 40
EFFICIENCY (%)
V
IN
(V)
LOAD = 1A
LOAD = 500mA
0
100
90
80
70
60
50
5 10 15 20 25 30 35 40
EFFICIENCY (%)
V
IN
(V)
LOAD = 300mA
LOAD = 200mA
LOAD = 100mA
Figure 1. DC1687A Efficiency in PWM Mode Figure 2. DC1687A Efficiency in Burst Mode Operation