DC1237A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1237
DUAL SYNCHRONOUS BOOST CONVERTER
LTC3527
DESCRIPTION
Demonstration circuits 1237A-A and 1237A-B are
dual 800/400mA high efficiency synchronous boost
converters. With a light load, the boost converters
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 voltage.
Separate input terminals are provided for each converter, and a jumper for paralleling the two inputs.
Terminals and jumpers for separately shutting down
or sequencing each regulators output and individual
Power-Good outputs are included. Jumpers are also
provided for selecting a total of six output voltages,
selecting BURST or PWM operation and switching
frequency. The 16-pin 3X3 mm QFN thermally enhanced package combined with the high switching
frequency provides a very tiny multi output solution.
The LTC3537 also features output disconnect and the
input voltage can be greater or less than the output
voltage.
This demonstration circuit allows the user to quickly
evaluate the LTC3527 performance. Jumpers make
selecting different output voltages simple while terminals on the board allow easy hookup to input supplies and output loads.
Demonstration circuit 1237A-B (LTC3527-1) has an
active pull-down to quickly discharge the output capacitor when manually shutdown.
Design files for this circuit board are available. Call
the LTC factory.
LTC and Burst Mode are trademarks of Linear Technology Corporation
Table 1. Typical Specifications (25°C)
Conditions
Input Voltage Range VIN
Limits
0.7V to 5.5V
Converter 1, 3V VOUT
VIN = 1.2V, IOUT = 100mA
3V ± 3%
Converter 1, 3.3V VOUT
VIN = 1.2V, IOUT = 100mA
3.3V ± 3%
Converter 1, 5V VOUT
VIN = 1.2V, IOUT = 100mA
5.0V ± 3%
Output Ripple Voltage (burst mode)
VIN = 1.5V, VOUT = 3.3V IOUT = 15mA
40mV p-p
Output Ripple Voltage (fixed frequency, 1.2MHz)
VIN = 1.5V, VOUT = 3.3V IOUT = 200mA
10mV p-p
Boost Efficiency (1.2MHz)
VIN = 1.8V, VOUT = 3.3V IOUT = 100mA
88%
Converter 2, 1.8V VOUT
VIN = 1.2V, IOUT = 50mA
1.8V ± 3%
Converter 2, 2.85V VOUT
VIN = 1.2, IOUT = 50mA
2.85V ± 3%
Converter 2, 3.3V VOUT
VIN = 1.2V, IOUT = 50mA
3.3V ± 3%
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1237
DUAL SYNCHRONOUS BOOST CONVERTER
Converter 1
Select VOUT
Input
Power
Supply
0 to [email protected]
Resistive
Loads
Converter 2
Select VOUT
A
-
V
V
+
Converter 1
A
VIN pin select
Converter 2
VIN1 Input
V
Upper position
parallels VIN1
& VIN2 pins
A
VIN2 Input
Select
PWM
or BURST
Mode
Converter 1
ON/OFF Inputs
Select
switching
frequency
Converter 2
ON/OFF Inputs
Select Converter 1
ON/OFF or SEQ
V
Monitor
Power Good
Outputs
V
Board Number
LTC Part Number
Part Marking
1237A-A
LTC3527EUD
LDDK
1237A-B
LTC3527EUD-1
LCXP
Figure 1. Demonstration Circuit Test Setup
VOUT
GND
Figure 2. Scope Probe Placement for Measuring Output Ripple Voltage
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1237
DUAL SYNCHRONOUS BOOST CONVERTER
QUICK START PROCEDURE
The LTC3527/3527-1 circuits can be evaluated using the setup shown in Figure 1. Simply placing
jumpers in various locations and measuring voltages can verify most of the features. It is recommended that the LTC3527 data sheet be nearby for
a more complete explanation of the various features
and specifications.
Using jumpers JP7 and JP8, select the desired output voltages (with no jumpers installed, the output
voltage is set for the highest voltage). Enable each
regulator by placing jumpers JP5 and JP6 in the ON
position; place JP1 in the “PARALLEL” position and
jumper JP2 to the “VIN1” position. When using
separate input supply voltages, place JP1 in the
“SINGLE” position and set jumper JP2 to the higher
of the two input voltages. Using JP3, select the desired mode (FIXED FREQUENCY or AUTO BURST)
and with JP4, select the desired switching frequency (1.2MHz or 2.2MHz).
Connect voltmeters and ammeters as shown in the
Figure 1 test setup. Connect a power supply to the
VIN1 and GND terminals and suitable load resistors
on the two VOUT 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 capacitance
near the input terminals.
With a light load (1k resistor) at each output, begin
increasing the input power supply voltage. At approximately 700mV, the output will rise to the selected regulated voltage. When the output voltage
exceeds the input voltage by at least 240mV, the
converter powers itself from the output instead of
the input. This feature allows the input voltage 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.
Increase the input voltage to approximately 1.5V or
more and increase each load current. The maximum
load current depends on the input and output voltage settings. A data sheet curve shows the maximum output current for different input and output
voltages.
Using voltmeters, verify each converter 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 placement shown in Figure 2. Typical Electrical Specifications are shown in table 1.
VOUT1
5V
4V
3V
2V
1V
0V
VOUT2
PGOOD2
SHDN2
PGOOD1
200µs/div
Figure 3. Voltages at start-up with VOUT1 sequenced to
VOUT2
Moving jumpers JP5 or JP6 to the OFF position can
individually shut down either regulator. Shutting
down the Boost Converter drops the converter’s
output voltage to near 0V. The LTC3527-1 has an
active pull-down to quickly discharge the output
capacitor when manually shutdown.
Jumpers JP5 and JP6 also can also be set for regulator output voltage sequencing. Depending on the
jumper setting, one of the regulators will remain
shut down until the other regulator has reached
regulation.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1237
DUAL SYNCHRONOUS BOOST CONVERTER
The PWRGOOD open drain output terminals are
high when the output voltage is in regulation and
pull low if the output voltage is approximately 10%
low, for any reason. Figure 3 shows various waveforms with VOUT1 sequenced to VOUT2. VOUT1 is
only allowed to be ON when VOUT 2 is in regulation. This is done by connecting the PGOOD2 to
SHDN1.
When Vin is near VOUT and in the range of approximately 300mV to 100mV below Vout, the converters are approaching the switch minimum ON
time resulting in an increased output voltage ripple
similar to BURST mode operation. This ripple can
be reduced by increasing the output capacitance.
The input voltage can exceed the output voltage and
still maintain regulation, although the maximum
output current is less and efficiency is lower.
With JP3 in the Auto Burst position, the converters
will operate in a low quiescent current burst mode,
provided both converters are under light load. Increasing the load current of either converter will
force both converters into fixed frequency (PWM)
mode.
Applications with an input of 1.6V or less boosting
to a voltage between 3V and 5V out, requiring
BURST mode operation, must use the 1.1MHz
Switching frequency. Using the higher frequency
will result in higher light load quiescent current. See
data sheet curves “Burst Mode Threshold Current
vs VIN” for additional information.
When evaluating the circuit at low input voltages, it
is important to monitor the input voltage 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 terminals dropping below the minimum
voltage required for operation.
Additional pc board pads are provided for an optional input bypass capacitor (C1). It maybe necessary when using long wires between the power
supply and circuit board, or for adding a tantalum
capacitor to minimize input voltage transients that
may occur when the input is hot-switched. Also,
pads on the board are provided for adding small
Schottky diodes, which can increase efficiency
slightly under some conditions. But adding these
diodes defeat the output disconnect and short circuit protection features.
See LTC3527 Data Sheet for additional information
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1237
DUAL SYNCHRONOUS BOOST CONVERTER
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