DEMO CIRCUIT 975
QUICK START
LT3482
GUIDE
LT3482
DC/DC Boost Converter for APD Bias
DESCRIPTION
Demonstration circuit 975A is a DC/DC Converter
for APD Bias featuring the LT3482 in a 3mm x
3mm QFN package. This demo circuit is designed
to convert a 3V-12V source to 80V at 2mA. The
circuit runs at 1.1MHz but can be easily pro-
grammed to run at 650KHz (inductor and other
components might need to change for such case).
The LT3482 features a 48V, 260mA switch, in-
tegrated Schottky diodes and a high side cur-
rent monitor which provides a current propor-
tional to the APD current. This current can be
used as a reference to digitally program the out-
put via the CTRL pin.
This circuit is specifically designed for APD bias
and is optimized for performance, solution size and
profile. To further reduce the solution size, induc-
tors such as Taiyo Yuden BRL2012B type can
be used though efficiency will suffer about 10%.
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.
LT is a registered trademark of Linear Technology Corporation.
PERFORMANCE SUMMARY DC975A
SYMBOL
V
IN
V
OUT
V
OUT
RIPPLE
FS
Specifications are at TA = 25°
C
MIN
3
75
75
TYP
80
80
500
1.1
MAX
12
85
85
UNITS
V
V
V
µV
MHz
PARAMETER
Input Supply Range
Output Voltage Range
Output Voltage Range
Switching frequency
CONDITIONS
V
IN
= 3V, I
LOAD
= 2mA
V
IN
= 12V, I
LOAD
= 2mA
V
IN
= 3.6V, I
LOAD
= 2mA
QUICK START PROCEDURE
Demonstration circuit 975 is easy to set up to
evaluate the performance of the LT3482. Refer to
Figure 1. for proper measurement equipment
setup and follow the procedure below:
NOTE.
When measuring the output voltage ripple, use a BNC cable
to connect J1 to the oscilloscope. Set the oscilloscope to AC couple,
2mV/division. That should yield the results shown in Figure 2 (Make
sure there are no test cables connected to the APD node).
3.
Connect a 40K resistor from APD to GND.
4.
Turn on the power at the input.
5.
Check for the proper output voltage. Vout1 =
75V to 85V.
NOTE.
If there is no output, temporarily disconnect the load to
make sure that the load is not set too high.
1.
Place jumper in the following position:
JP1
Run
2.
With power off, connect the input power supply
to Vin and GND.
6.
Once the proper output voltage is established,
adjust the load within the operating range and
observe the output voltage regulation, ripple
voltage, efficiency and other parameters.
1
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