1.5MHZ SYNCHRONOUS BOOST / SYNCHRONOUS BUCK CONVERTERS AND LDO
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1326A
LTC3100
DESCRIPTION
Demonstration circuit 1326A consists of three
voltage regulators; a synchronous boost, a syn-
chronous buck and a linear LDO. The high effi-
ciency DC/DC converters feature 700mA
switches for the boost, 250mA for the buck and
a 100mA rating for the LDO regulator.
With a light load, the boost converter can
startup with an input voltage as low as 700mV
and once started, the input can go as low as
500mV while maintaining a regulated output.
Buck converter requires 1.8V minimum input.
Separate input terminals are provided for each
switch mode converter, and a jumper for paral-
leling the two converter inputs or powering the
buck from the output of the boost. The LDO
regulator is always powered from the boost
output.
Jumpers are included for separately shutting
down the boost regulator or shutting down or
sequencing the buck and LDO regulators.
Table 1. Typical Specifications (25°
C)
Conditions
Boost Converter Input Voltage Range V
IN
Boost Converter, 1.8V V
OUT
Boost Converter, 3.3V V
OUT
Boost Converter, 5V V
OUT
Boost Output Voltage Ripple (burst mode)
Boost Output Voltage Ripple (PWM)
Buck Converter, 1.2V V
OUT
Buck Converter, 1.5V V
OUT
Buck Converter, 1.8V V
OUT
Buck Output Voltage Ripple (burst mode)
Buck Output Voltage Ripple (PWM)
LDO Regulator, 1.5V V
OUT
LDO Regulator, 2.85V V
OUT
LDO Regulator, 3V V
OUT
V
IN
= 1.2V, I
OUT
= 100mA
V
IN
= 1.2V, I
OUT
= 100mA
V
IN
= 1.2V, I
OUT
= 100mA
V
IN
= 1.5V, V
OUT
= 3.3V, I
OUT
= 10mA
V
IN
= 1.5V, V
OUT
= 5V, I
OUT
= 100mA
V
IN
= 2V, I
OUT
= 100mA
V
IN
= 2V, I
OUT
= 100mA
V
IN
= 2V, I
OUT
= 100mA
V
IN
= 2V, V
OUT
= 1.5V, I
OUT
= 10mA
V
IN
= 2V, V
OUT
= 1.5V, I
OUT
= 100mA
V
IN
= 3.3V from V
OUT
Boost, I
OUT
= 50mA
V
IN
= 3.3V from V
OUT
Boost, I
OUT
= 50mA
V
IN
= 3.3V from V
OUT
Boost, I
OUT
= 50mA
Limits
0.68V to 5.5V
1.8V ± 3%
3.3V ± 3%
5.0V ± 3%
25mV p-p
10mV p-p
1.2V ± 3%
1.5V ± 3%
1.8V ± 3%
10mV p-p
5mV p-p
1.5V ± 3%
2.85V ± 3%
3.0V ± 3%
Jumpers are also provided for selecting a total
of nine output voltages and selecting BURST or
PWM operation. The 16-pin 3X3 mm QFN
thermally enhanced package combined with the
high switching frequency provides a very tiny
multi output solution. The LTC3100 boost con-
verter also features output disconnect and the
input voltage can be greater or less than the
output voltage. Power Good terminals for the
boost and buck converters are also included.
This demonstration circuit allows the user to
quickly evaluate the LTC3100 performance.
Jumpers make selecting different output volt-
ages simple while 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 Technol-
ogy Corporation
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1.5MHZ SYNCHRONOUS BOOST / SYNCHRONOUS BUCK CONVERTERS AND LDO
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1326A
Board Number
1326A
LTC Part Number
LTC3100EUD
Part Marking
LDJR
BUCK Input
V
BOOST Input
Input
Power
Supply
0 to 5V@1A
-
+
A
Select
PWM
or BURST
Mode
Resistive
Loads
Boost
ON/OFF
Select VOUT
BOOST
Select VOUT
LDO
A
V
A
V
Select Buck
Input Power
Select Buck
ON/OFF or SEQ
Select LDO
ON/OFF or SEQ
BOOST
Converter
LDO
Reguator
BUCK
Converter
V
V
Monitor
Power Good
Outputs
GND
Select VOUT
BUCK
A
V
Figure 1. Demonstration Circuit Test Setup
QUICK START PROCEDURE
The LTC3100 circuit can be evaluated using
the setup shown in Figure 1. Simply placing
jumpers in various locations, attaching output
loads and measuring voltages can verify most
of the features. It is recommended that the
LTC3100 data sheet be nearby for a more
complete explanation of the various features
and specifications.
Place the BUCK INPUT jumper (JP1) in the
“PARALLEL” position. Using jumpers JP5,
JP6 and JP7, select the desired output volt-
ages (with no jumpers installed, the output
voltage is set for the highest voltage). Note;
set the boost output voltage to 3.3V to provide
sufficient input voltage for the LDO regulator.
Enable each regulator by placing jumpers
JP2, JP3 and JP4 in the ON position. Select
the desired mode Using JP8 (PWM or
BURST).
Connect voltmeters and ammeters as shown
in the Figure 1 test setup. Connect a power
supply to the BUCK IN and GND terminals
and suitable load resistors on the three output
and GND terminals. Avoid excessive wire
lengths between the input power supply and
the demonstration board. Wire lengths greater
than 18 inches may require additional capaci-
tance near the input terminals.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1326A
1.5MHZ SYNCHRONOUS BOOST / SYNCHRONOUS BUCK CONVERTERS AND LDO
With a light load (1k resistor) at each output,
begin increasing the input power supply volt-
age. At approximately 700mV, the boost out-
put will rise to the selected regulated voltage.
When the boost output voltage exceeds the
input voltage by at least 240mV, the boost
converter powers itself from the output instead
of the input. This feature allows the input volt-
age to drop as low as 500mV (at light loads)
and still maintain a regulated output voltage. A
data sheet curve shows the minimum resistive
load vs. Vin that will allow the boost converter
to start. Undervoltage lockout for the buck
converter keeps it off for voltages below 1.6V
(typ).
Increase the input voltage to approximately
2V and increase each load current. The
maximum load current for the boost converter
depends on the input and output voltage set-
tings while the maximum load for the buck
and LDO regulators are 250mA and 100mA
respectively. A data sheet curve shows the
maximum boost converter output current for
different input and output voltages.
Using voltmeters, verify each regulator output
voltage for each of the output voltage options.
Output ripple voltage and startup waveforms
can be observed using an oscilloscope. In
Burst mode with light load current, the output
ripple voltage is higher than in non-burst
mode. Observe proper scope probe place-
ment shown in Figure 3. Typical Electrical
Specifications are shown in table 1.
With JP3 in the burst position, under light
load, each converter can operate in a low qui-
escent current burst mode, independent of the
other converter. As the load current increases,
the converter transitions into fixed frequency
(PWM) mode. In the PWM position, the con-
verters are operating in the low output ripple,
constant frequency mode.
BOOST Output
3.3V
2.85V
BOOST
Power Good
LDO Output
RUNBST
Buck Output
1.2V
BUCK Power Good
500µs/div
Figure 2. Sequenced Voltages at Start-up
Moving jumpers JP2, JP3 or JP4 to the OFF
position can individually shut down the re-
spective regulator. Since the LDO regulator
receives power from the boost converter,
shutting down the boost converter will also
cause the LDO output to drop
Jumpers JP2 and JP4 also can also be set to
provide output voltage sequencing. Depend-
ing on the jumper settings, one of the regula-
tors will remain shut down until the other regu-
lator has reached regulation.
The PWRGOOD open drain output terminals
are high when the output voltage is in regula-
tion and pull low if the output voltage is ap-
proximately 10% low, for any reason. Figure 2
shows various waveforms with the Buck out-
put sequenced to the boost output and the
LDO output sequenced to the Buck output.
Placing JP2 and JP4 in the SEQ position con-
nects the power good output of the boost con-
verter to the run input of the Buck converter,
and the power good output of the buck con-
verter to the run input of the LDO regulator.
Sequencing provides an orderly startup of one
or more of the output voltages.
The DC/DC converters have separate input
pins and can be powered from different volt-
age sources. JP1 allows the Buck converter to
be powered from BUCK IN pin, BOOST IN pin
(parallel) or powered from the boost convert-
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1326A
1.5MHZ SYNCHRONOUS BOOST / SYNCHRONOUS BUCK CONVERTERS AND LDO
ers output. The boost converter input voltage
can exceed the output voltage and still main-
tain regulation, although the load current is
less and efficiency is lower.
With input voltage applied to the boost con-
verter, shutting it down completely opens the
input-to-output current path, unlike other boost
converters that do not have an output discon-
nect feature.
When evaluating the circuit at low input volt-
ages, it is important to monitor the input volt-
age directly at the input terminals of the circuit
board. At very low input voltages, voltage
drops in the power supply wire and Ammeter
will result in the input voltage at the input ter-
minals dropping below the minimum voltage
required for operation.
Additional pc board pads are provided on the
backside for optional input bypass capacitors
(C1 and C13). These maybe necessary when
using long wires between the power supply
and circuit board, or for adding tantalum ca-
pacitors to minimize input voltage transients
that may occur when the input is hot-switched.
Also, pads on the board backside are pro-
vided for adding small Schottky diodes (D1
and D2), which can increase converters effi-
ciency. When verifying output ripple, it is im-
portant to use the scope probe connection as
shown in figure 3.
See LTC3527 Data Sheet for additional information
V
OUT
GND
Figure 3. Scope Probe Placement for
Measuring Output Ripple Voltage
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1326A
1.5MHZ SYNCHRONOUS BOOST / SYNCHRONOUS BUCK CONVERTERS AND LDO
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