DC765A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 765
GENERAL PURPOSE POSITIVE/NEGATIVE CONVERTERS
LT3479EDE
DESCRIPTION
Demonstration circuit 765 is a general purpose assembly containing 1MHz, positive and negative converters featuring the LT3479. The demo circuit demonstrates small size and low component count in a
Boost Circuit and an Inverting Circuit. The Boost Converter is set up to convert a 2.5V-4.2V input to 7V
output at 300mA constant current to drive two LXHLPW09 LUMILEDs but can be easily configured to run
as a general purpose boost providing 7V at 600mA
(See instructions on the schematic). The Inverting
Circuit generates a -5V output at 600mA from an input of 2.5V to 12V. The boost circuit was designed to
demonstrate the ability to drive high power LEDs with
a constant current and a minimum sense resistor
power loss. Both circuits demonstrate the capacitor
programmable Soft-Start feature, advantages of the
1MHz constant switching frequency and the internal
42V switches. Both outputs on this demo circuit can
be modified for higher voltages. These circuits are
intended for space-conscious applications such as
high power LED drivers, DSL modems and Distributed Power.
Design files for this circuit board are available. Call
the LTC factory.
LTC is a trademark of Linear Technology Corporation
Table 1. Performance Summary (TA = 25°C)
PARAMETERS FOR BOOST CIRCUIT (USED AS GENERAL
PURPOSE BOOST)
CONDITION
VALUE
Minimum Input Voltage
2.5V
Maximum Input Voltage
4.2V
Output Voltage VOUT
Vin = 2.5V to 4.2V (Powering LUMILEDs)
6V to 7.5V
Typical efficiency
VIN =3.3V, Vout = [email protected] (Powering
LUMILEDs)
83%
Typical efficiency as regular Boost converter
Vin=3.3V, [email protected]
85%
Typical Output Ripple VOUT as regular Boost converter
Vin=3.3V, [email protected]
60mV
PARAMETERS FOR INVERTING CIRCUIT
VALUE
Output Voltage VOUT
VIN = 2.5V, IOUT =0-600mA
-5V ±3%
Output Voltage VOUT
VIN = 12V, IOUT =0- 600mA
-5V ±3%
Typical Output Ripple VOUT
VIN = 3.3V, IOUT = 600mA
10mVP–P
Typical efficiency
VIN = 7V, Vout = [email protected]
74%
Input capacitors C16 and C17 used only for operation with long inductive input leads.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 765
GENERAL PURPOSE POSITIVE/NEGATIVE CONVERTERS
QUICK START PROCEDURE
Demonstration circuit 765 is easy to set up to evaluate the performance of the LT3479. Refer to Figure 1
for proper measurement equipment setup and follow
the procedure below:
NOTE: When measuring the input or output voltage
ripple, 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 VIN or VOUT and GND terminals. See Figure 1 for proper scope probe technique.
1.
For Boost converter circuit: Place jumper in the
following position:
JP1
2.
3.
4.
NOTE: If
there is no output, there will be no light.
Make sure that the unit is properly hooked up.
5.
Once the proper output voltages are established,
vary the input voltage within the operating range
and observe the output voltage regulation, ripple
voltage, efficiency and other parameters.
6.
For Inverter circuit: Place jumper in the following
position, and repeat tests 2 to 5.
JP2
On
With power off, connect the input power supply to
VIN and GND.
Before applying power place a shield on top of D2
and D3 and avoid looking directly at the light.
Check for the proper output voltages. VOUT will
change between 6V and 7.5V, depending on the
forward voltage of the LUMILEDs D2 and D3.
On
7.
Apply input voltage and monitor the output.
8.
Once the proper output voltages are established,
adjust the input and load within the operating
range and observe the output voltage regulation,
ripple voltage, efficiency and other parameters.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 765
GENERAL PURPOSE POSITIVE/NEGATIVE CONVERTERS
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 765
GENERAL PURPOSE POSITIVE/NEGATIVE CONVERTERS
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