DC1368A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1368A
ADJUSTABLE LDO LINEAR REGULATORS IN PARALLEL
LT3080EDD-1
DESCRIPTION
Demonstration circuit 1368A shows adjustable linear
regulators in parallel using LT3080-1. Architected as
a precision current source and voltage follower, it
allows this new regulator to be used in many applications requiring high current, adjustability to zero output, and no heat sink. Also the device brings out the
collector of the pass transistor to allow low dropout
operation when used with multiple supplies.
A key feature of the LT3080-1 is the capability to
supply a wide output voltage range. By using a reference current through a single resistor, the output
voltage can be programmed to any level between
zero and 36V. The DC1368A has a reduced input
voltage 25V due to input capacitor voltage rating.
LT3080-1 incorporates an internal ballast resistor to
allow direct paralleling of devices without the need
for PC board resistors or sensor resistors. By direct
paralleling of four LT3080-1 regulators, the DC1368A
is capable of delivering up to 4.4A output current. It
can be used as a high current linear regulator, post
regulator for switching supply, variable voltage supply or low output voltage power supply.
Internal protection circuitry includes current limiting
and thermal limiting.
LT3080-1 regulator is offered in 8-lead MSOP (with
an Exposed Pad for better thermal characteristics)
and a 3mm × 3mm DFN.
The LT3080-1 datasheet gives a complete description
of the part, operation and application information.
The datasheet should be read in conjunction with this
quick start guide for working on or modifying the
demo circuit 1368A.
Design files for this circuit board are available.
Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Table 1. Performance Summary ( TA = 25oC )
PARAMETER
CONDITION
VALUE
Minimum Vin Voltage
Vout=1.2V
1.7V
Maximum Vin Voltage
Minimum Vcontrol Voltage
25V
Vout=1.2V
Maximum Vcontrol Voltage
Output Voltage
25V
Iout=4.4A
Minimum Output Current
Maximum Output Current
2.8V
1.17V ±3%
4mA
Vin-Vout<2.5V
4.4A
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1368A
ADJUSTABLE LDO LINEAR REGULATORS IN PARALLEL
QUICK START PROCEDURE
The DC1368A is easy to set up to evaluate the performance of the LT3080-1. Refer to Figure 1. for
proper measurement equipment setup and following
the procedures below:
1.
Apply 1.7V across Vin (to Gnd), and 2.8V
across Vcontrol. Draw 4.4A of load current.
The measured Vout should be 1.17V ± 3%
(1.13V to 1.21V).
2.
Vary Vin from 1.7V to 25V, Vcontrol from
2.8V to 25V and the load current from 4mA to
4.4A. Vout should measure 1.19V ± 5%
(1.13V to 1.25V).
Note: Make sure the power dissipation is limited below the thermal limit.
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
INPUT VOLTAGE RANGE
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1368A
ADJUSTABLE LDO LINEAR REGULATORS IN PARALLEL
The guaranteed Vin dropout voltage is 0.5V at 4.4A,
the guaranteed Vcontrol dropout voltage is 1.6V at
4.4A. The maximum Vin and maximum Vcontrol is
reduced to 25V due to the input capacitor voltage rating.
DUAL SUPPLY OR SINGLE SUPPLY
Use two separate supplies for Vin and Vcontrol, a low
dropout voltage can be achieved on the Vin pin and the
power dissipation is minimized. Alternatively, Tying the
Vcontrol to Vin through a zero ohm jump resistor R1
on board, a single supply is sufficient to drive the
demo circuit 1368A. AVOID USING A LONG WIRE TO
TIE VCONTROL AND VIN.
OUTPUT CURRENT
The output current will decrease at high input-tooutput differential. The actual current output is further
limited by the thermal shutdown function, which is
related to the board thermal dissipation.
THERMAL IMAGE
An example thermal image shows the temperature distribution on board. The test is done in still air at room temperature with average 2.0W power dissipation in each LT3080-1.
BYPASS CAPACITOR
Since the SET pin is a high impedance node, unwanted
signals may couple into the SET pin and cause erratic
behavior. This will be most noticeable when operating
with minimum output capacitors at full load current.
The easiest way to remedy this is to bypass the SET
pin with a small amount of capacitance from SET to
ground, 10pF to 20pF is sufficient. A 0.01uF bypass
capacitor is used on the demo board to provide a lownoise output. Please refer to datasheet for details.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1368A
ADJUSTABLE LDO LINEAR REGULATORS IN PARALLEL
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