QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1483
DUAL 550MA SYNCHRONOUS BOOST CONVERTER
LTC3535
DESCRIPTION
Demonstration circuit 1483 is a dual high efficiency
synchronous boost converter capable of operating
with an input voltage range from 0.8V to 5V. The 12
lead 3X3 mm thermally enhanced DFN package with a
1MHz switching frequency and the 550mA internal
switches provide a very tiny step-up solution. The
LTC3535 can be powered from separate input sup-
plies that can be greater or less than the output volt-
age although the efficiency and maximum output cur-
rent is reduced when V
IN
is greater than V
OUT
. Also fea-
tured is burst mode operation for high efficiency at
low current levels and a true input-to-output discon-
nect which allows the output to drop to zero volts
when shutdown and provides soft start and current
limiting.
This demonstration circuit allows the user to quickly
evaluate the LTC3535 performance. Individual jump-
ers are provided for selecting a variety of output volt-
ages from 1.8V to 5V. Jumpers also allow separate
low quiescent current shutdown and the ability to
parallel the inputs. Terminals on the board allow easy
hookup to input supplies and output loads.
Design files for this circuit board are available. Call
the LTC factory.
LTC and Burst Mode are trademarks of Linear Technology Corporation
Table 1. Each Converter Typical Specifications (25°C)
V
IN
Input Voltage Range after startup
V
OUT1
3V
V
OUT1
3.3V
V
OUT1
5V
V
OUT2
1.8V
V
OUT2
2.85V
V
OUT2
3.3V
Output Ripple Voltage (burst mode)
Output Ripple Voltage (fixed frequency)
Efficiency
Efficiency
Minimum voltage is load current dependant
V
IN
= 1.5V, I
OUT
= 100mA
V
IN
= 1.5V, I
OUT
= 100mA
V
IN
= 1.5V, I
OUT
= 100mA
V
IN
= 1.5V, I
OUT
= 100mA
V
IN
= 1.5V, I
OUT
= 100mA
V
IN
= 1.5V, I
OUT
= 100mA
V
IN
= 1.2V, V
OUT
= 3.3V I
OUT
= 10mA
V
IN
= 1.2V, V
OUT
= 3.3V I
OUT
= 100mA
V
IN
= 1.2V, V
OUT
= 1.8V I
OUT
= 10mA
V
IN
= 1.8V, V
OUT
= 3.3V I
OUT
= 100mA
0.5V to 5V
3V ± 3%
3.3V ± 3%
5.0V ± 3%
1.8V ± 3%
2.85V ± 3%
3.3V ± 3%
45mV p-p
15mV p-p
84%
88%
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1483
DUAL 550MA SYNCHRONOUS BOOST CONVERTER
QUICK START PROCEDURE
The boost converters can be evaluated using the
setup shown in Figure 1. Set jumper JP1 to the
PARALLEL position and JP2 and JP3 to ON. Select
the desired output voltages using jumpers JP4 and
JP5. (With no jumpers installed, the output voltage
is set for the maximum). Connect voltmeters and
ammeters as shown on the test setup. Connect a
power supply to the V
IN
and GND terminals and suit-
able load resistors between VOUT and GND.
With a light load (1k resistor) at one of the outputs,
begin increasing the input power supply voltage. At
approximately 800mV, the output will rise to the
selected regulated voltage. Increase the input volt-
age to approximately 1.5V and increase the load
current.
Note the excellent load regulation when going from
a light load current to a heavier load, but it is impor-
tant to monitor the input voltage directly at the in-
put terminals of the circuit board. At very low input
voltages, voltage drops in the power supply wire,
VOUT2
ON/OFF
VOUT2 ON OFF
connections and Ammeter will result in the input
voltage at the input terminals dropping below the
minimum voltage required for operation.
Additional pc board pads are provided for optional
input bypass capacitors (C1, C3). These may be
necessary when using long wires between the
power supply and circuit board, or for adding tanta-
lum capacitors to minimize input voltage transients
that may occur when the input is hot-switched.
Also, pads on the board backside are provided for
adding small Schottky diodes, which can increase
efficiency slightly under some conditions. But add-
ing a diode defeats the output disconnect and short
circuit protection features.
When verifying output ripple use the scope probe
connection as shown in figure 2.
In Burst mode with light load current, the output
ripple voltage is higher than in non-burst mode.
See the LTC3535 Data Sheet for additional data.
Select
VOUT2
Voltage
Resistive
Loads
Input
+
Power
Supply
-
A
A
V
V
Seperate or
Parallel Inputs
Converter 1 Input
VOUT1 ON OFF
Select
VOUT1
Voltage
V
A
VOUT1
ON/OFF
Package marking LDWV
Figure 1. Demonstration Circuit Test Setup
V
OUT
GND
Figure 2. Scope Probe Placement for Measuring Output Ripple Voltage.
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