DC995A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 995A
ADJUSTABLE LDO LINEAR REGULATOR
LT3080EDD
DESCRIPTION
Demonstration circuit 995A is an adjustable 1.1A linear regulator featuring LT®3080. 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 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 DC995A has a reduced input voltage 25V
due to input capacitor voltage rating. And DC995A is
capable of delivering up to 1.1A output current.
Therefore, the DC995A 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 regulator is offered in 8-lead MSOP (with an
Exposed Pad for better thermal characteristics), a
3mm × 3mm DFN, 5-lead TO-220 and a simple-touse 3-lead SOT-223 version.
The LT3080 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 995A.
If more output current is required or heat-spreading
is needed, LT3080 can be easily paralleled. See
DC1294A for details.
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=1.8V
2.3V
Maximum Vin Voltage
Minimum Vcontrol Voltage
25V
Vout=1.8V
Maximum Vcontrol Voltage
Output Voltage
25V
JP1, Vout=1.8V
1.8V ±3%
JP1, Vout=0V-5V
0V-5V±3%
Minimum Output Current
Maximum Output Current
3.4V
1mA
Vin-Vout<3.5V
1.1A
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 995A
ADJUSTABLE LDO LINEAR REGULATOR
QUICK START PROCEDURE
The DC995A is easy to set up to evaluate the performance of the LT3080. Refer to Figure 1. for proper
measurement equipment setup and following the
procedures below:
1.
Before proceeding to test, use VOUT Select
jumper JP1 for the desired output voltage
(1.8V or 0V-5V). If the output voltage is different from the above values, use the USER
option and install R3. Select R3 according to
the following equation: R3 = VOUT .
Vcontrol. Draw 1.1A of load current. The
measured Vout should be 1.8V ± 3% (1.766V
to 1.875V).
3.
Vary Vin from 2.3V to 25V, Vcontrol from
3.4V to 25V and the load current from 1mA to
1.1A. Vout should measure 1.8V ± 3%
(1.766V to 1.875V).
Note: Make sure the power dissipation is limited below the thermal limit.
10µA
2.
Assume 1.8V is the desired output. Apply
2.3V across Vin (to Gnd), and 3.4V across
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 995A
ADJUSTABLE LDO LINEAR REGULATOR
INPUT VOLTAGE RANGE
The guaranteed Vin dropout voltage is 0.5V at 1.1A,
the guaranteed Vcontrol dropout voltage is 1.6V at
1.1A. 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 on
board, a single supply is sufficient to drive the demo
circuit 995A. AVOID USING A LONG WIRE TO TIE
VCONTROL AND VIN.
OUTPUT CURRENT
The output current will decrease at high input-to-output differential. The actual current output is further limited by the
thermal shutdown function, which is related to the board thermal dissipation. A typical curve is provided using the
demo circuit 995A at room temperature. DO NOT CONTINUOUSLY OPERATE THE LT3080 TO THE THERMAL LIMIT,
WHICH MAY IMPAIR THE DEVICE RELIABILITY. MAXIMUM JUNCTION TEMPERATURE IS 125oC.
Thermal Limit & Current Limit
1.4
Thermal Limit
LOAD CURRENT (mA)
1.2
Current Limit
1
0.8
0.6
0.4
0.2
0
0
5
10
15
20
25
30
Vin - Vout (V)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 995A
ADJUSTABLE LDO LINEAR REGULATOR
THERMAL IMAGE
An example thermal image shows the temperature distribution on board. The test is done in still air at room temperature with 2.2W power dissipation in LT3080.
Thermoteknix
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 995A
ADJUSTABLE LDO LINEAR REGULATOR
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