QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 634
AVALANCHE PHOTODIODE BIAS SUPPLY
LT1930A
DESCRIPTION
Demonstration circuit 634 is a low noise ava-
lanche photodiode (APD) bias supply featuring the
LT1930A.
This circuit takes an input voltage from 3V to 5.5V.
The output voltage can be adjusted from 30V to
90V by applying a control voltage (4.5V to 0V) to
the VPROGRAM pin.
Table 1. Performance Summary
PARAMETER
Typical Output Ripple (V
OUT
= 30V)
Typical Output Ripple (V
OUT
=50V)
Typical Output Ripple (V
OUT
=70V)
Nominal Switching Frequency
CONDITION
V
IN
= 3V, LOAD = 47kΩ, 10MHz bandwidth
V
IN
= 3V, LOAD = 47kΩ, 10MHz bandwidth
V
IN
= 3V, LOAD = 47kΩ, 10MHz bandwidth
VALUE
340µV
P–P
400µV
P–P
535µV
P–P
2.2MHz
The 2.2MHz switching frequency helps to mini-
mize the circuit size.
Design files for this circuit board are available.
Call the LTC factory.
QUICK START PROCEDURE
Demonstration circuit 634 is easy to set up to
evaluate the performance of the LT1930A. Follow
the procedure below:
1.
Before hooking up the input supply and control
3.
Make sure your setup is safe and the RUN/SD
jumper is in the RUN position.
Remember, the
output voltage will be 90V when the control
voltage is 0V.
4.
Turn on the power supplies and meters. Adjust
voltage to the demo board, set the input supply
voltage between 3V and 5.5V; set the control
voltage between 0V and 4.5V. Then turn off the
supplies.
2.
Connect input supply, control voltage, load and
the control voltage for the desired output volt-
age.
5.
Once the proper output voltage is established.
meters as shown in Figure 1. If you want to
monitor output ripple, also connect the BNC
connector to the oscilloscope through a coaxial
cable.
Check the ripple voltage via the coaxial cable.
(See
Application Note 92 for detailed dis-
cussion on low noise measurement tech-
niques.)
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 634
AVALANCHE PHOTODIODE BIAS SUPPLY
Figure 1. Proper Measurement Equipment Setup
Figure 2. LT1930A Output Ripple (V
IN
=3V, V
OUT
=30V, LOAD = 47kΩ; 0.5mV/div ac coupled; 10MHz
bandwidth)
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 634
AVALANCHE PHOTODIODE BIAS SUPPLY
Figure 3. LT1930A Output Ripple (V
IN
=3V, V
OUT
=50V, LOAD = 47kΩ; 0.5mV/div ac coupled; 10MHz
bandwidth)
Figure 4. LT1930A Output Ripple (V
IN
=3V, V
OUT
=70V, LOAD = 47kΩ; 0.5mV/div ac coupled; 10MHz
bandwidth)
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 634
AVALANCHE PHOTODIODE BIAS SUPPLY
4
