DC1423A - Demo Manual

DEMO CIRCUIT 1423
QUICK START LT3571
GUIDE
LT3571
DC/DC Boost Converter for APD Bias
DESCRIPTION
Demonstration circuit 1423 is a DC/DC Boost
Converter for APD Bias featuring the LT3571 in
3mm x 3mm QFN package. This demo board is
designed to convert a 5V-12V source to 50V at
2mA. The demo board includes a fast transient
response test circuit on the back side. Remove C4
for fast transient evaluation. To control the output
voltage via the CTRL pin, remove R6. The circuit is
designed for 1MHz operation but can be easily
programmed for any frequency between 250KHz
and 2MHz.
The LT3571 features a 75V, 350mA switch, integrated diode, and high side current monitor which
provides a current proportional to the APD current.
Other features include Frequency Synchronization,
Programmable Current Limit Protection, and Internal Soft-Start. The LT3571 datasheet gives a com-
PERFORMANCE SUMMARY
SYMBOL
VIN
VOUT
VOUT
Ripple
Fs
PARAMETER
Input Supply Range
Output Voltage Accuracy
Output Voltage Accuracy
plete description of the part, its operation and application information. The datasheet must be read
in conjunction with this quick start guide for working on or modifying the demo circuit 1423.
For fast transient response demonstration: remove
C4 and any other capacitance or test probes
across APD node and carefully read APD Current
Monitor Transient Response section in the datasheet.
This circuit is specifically designed for APD bias
and is optimized for performance, solution size and
profile. Typical applications include APD bias, PIN
Diode bias, Optical Receivers and Modules, Fiber
Optic Network Equipment etc.
Design files for this circuit board are available.
Call the LTC factory.
Specifications are at TA = 25°C
CONDITIONS
VIN = 5V, ILOAD = 2mA
VIN = 12V, ILOAD = 4mA
VIN = 5V, ILOAD = 2mA
Switching Frequency
MIN
5
48
48
TYP
50
50
1mV
1
MAX
12
52
52
UNITS
V
V
V
MHz
QUICK START PROCEDURE
Demonstration circuit 1423 is easy to set up to
evaluate the performance of the LT3571. Refer to
Figure 1 for proper measurement equipment setup
and follow the procedure below:
NOTE. When measuring the output voltage ripple, connect an X1
probe from the oscilloscope to the APD terminals or a BNC cable to
J1. Set the oscilloscope amplitude to 2mV/div, and the coupling to
AC. Make sure there are no other cables connected to the APD
node.
1. Place jumper in the following positions:
JP1 Run
2. With power off, connect the input power supply
to Vin and GND.
3. Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed 12V.
1
LT3571
4. Connect A 25K resistor from APD to ground
and check for the proper output voltages. Vout
= APD = 49V to 51V.
NOTE. If there is no output, temporarily disconnect the load to
make sure that the load is not set too high.
5. Once the proper output voltages are established, adjust the input voltage within the operating range and observe the output voltage
regulation, ripple voltage, efficiency and other
parameters.
Figure 1. Proper Measurement Equipment Setup
2
LT3571
Figure 2. Schematic
3
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