DC720A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 720
HIGH VOLTAGE SYNCHRONOUS STEP-DOWN CONTROLLER
LT3800
DESCRIPTION
Demonstration Circuit 720 is a 200kHz high voltage,
synchronous current-mode DC/DC step-down converter featuring the LT3800.
The board operates from a Vin range of 20V – 55V
and outputs 12V @ 6.25A (75W). A soft-start feature
controls the output voltage slew rate at start-up, reducing current surges and voltage overshoots. The
modes of operation, Burst Mode, Discontinuous Current Mode and Continuous Current Mode, are jumper
selectable. Both Burst Mode and Discontinuous Current Mode increase the efficiency at light loads. Continuous Current Mode will maintain a constant
switching frequency regardless of the load current
required.
An Optional Boost Bias circuit is provided on the bottom side of the board for back-driving the LT3800
internal regulator from the output voltage. Customers
might want to use this optional circuit with modified
applications that have relatively high input voltages
and low (~ 5V) output voltages. In such applications,
the optional circuit can increase the overall efficiency
by reducing the power lost in the LT3800. The demonstration board has also been layed out with the option of doubling the switching MOSFETs to facilitate
higher output currents. The circuit design can be
modified for a Boost converter configuration.
This board is suitable for a wide range of industrial
control systems and particularly suitable for 12V/42V
automotive applications and 48V Telecom power supplies.
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)
PARAMETER
Vin Input Voltage Range
CONDITION
VALUE
20V 55V
Efficiency
20Vin, 6.25Aout
48Vin, 6.25Aout
55Vin, 6.25Aout
Switching Frequency
Output Voltage
Vout_ripple_pp
0 – 6.25Aout
95.6%
93.7%
93.2%
200kHz fixed.
12V
~ 50mV
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 720
HIGH VOLTAGE SYNCHRONOUS STEP-DOWN CONTROLLER
QUICK START PROCEDURE
DC720 is easy to set up to evaluate the performance
of the LT3800. Refer to Figure 1 for proper measurement equipment setup and follow the procedure
below:
1.
Apply a 0 – 6.25A Load across the Vout/Gnd turrets.
2.
Connect Voltmeters and Ammeters as shown in
Fig. 1.
3.
Connect a 0 - 60V Power Supply (or better) across
the Vin/Gnd turrets. Typically it’s best to set the
Current Limit of this Power Supply to its maximum
setting. The power supply must be capable of providing the required start-up power. If using a bench
power supply, a 60V/15A rated (or better) supply is
recommended. Set Vin to 20V – 55Vin.
4.
Make sure the SHDN/RUN jumper is in the RUN
position.
Figure 1. Proper Measurement Equipment Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 720
HIGH VOLTAGE SYNCHRONOUS STEP-DOWN CONTROLLER
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