DC1401A- Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1401A
ADJUSTABLE SINGLE RESISTOR LDO REGULATOR
LT3085EDCB
DESCRIPTION
Demonstration circuit 1401A is an adjustable 500mA
linear regulator featuring LT®3085. 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 LT3085 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 DC1401A has a reduced input voltage 25V
due to input capacitor voltage rating. And DC1401A
is capable of delivering up to 500mA output current.
Therefore, the DC1401A 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.
LT3085 regulator is offered in 8-lead MSOP (with an
Exposed Pad for better thermal characteristics) and
6-lead 2mm × 3mm DFN packages.
The LT3085 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 1401A.
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
JP1, Vout=1.2V
1.2V ±3%
JP1, Vout=1.8V
1.8V ±3%
JP1, Vout=2.5V
2.5V ±3%
JP1, Vout=3.3V
3.3V ±3%
JP1, Vout=5.0V
5.0V±3%
Minimum Output Current
Maximum Output Current
2.8V
1mA
Vin-Vout<6V
500mA
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1401A
ADJUSTABLE SINGLE RESISTOR LDO REGULATOR
QUICK START PROCEDURE
The DC1401A is easy to set up to evaluate the performance of the LT3085. Refer to Figure 1. for proper
measurement equipment setup and following the
procedures below:
1.
Before proceeding to test, use jumper JP1 for
the desired output voltage (1.2V, 1.8V, 2.5V,
3.3V or 5.0V). If the output voltage is different
from the above values, use the USER option
and install R6. Select R6 according to the following equation: R6 = VOUT .
Vcontrol. Draw 500mA of load current. The
measured Vout should be 1.2V ± 3% (1.174V
to 1.246V).
3.
Vary Vin from 1.7V to 25V, Vcontrol from
2.8V to 25V and the load current from 1mA to
500mA. Vout should measure 1.2V ± 3%
(1.174V to 1.246V).
Note: Make sure the power dissipation is limited below the thermal limit.
10µA
2.
Assume 1.2V is the desired output. Apply
1.7V across Vin (to Gnd), and 2.8V across
Figure 1. Proper Measurement Equipment Setup
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1401A
ADJUSTABLE SINGLE RESISTOR LDO REGULATOR
Figure 2. Measuring Input or Output Ripple
INPUT VOLTAGE RANGE
The guaranteed Vin dropout voltage is 0.5V at 500mA,
the guaranteed Vcontrol dropout voltage is 1.6V at
500mA. 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 short wire, a single supply is
sufficient to drive the demo circuit 1401A. 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. DO NOT
CONTINUOUSLY OPERATE THE LT3085 TO THE
THERMAL LIMIT, WHICH MAY IMPAIR THE DEVICE
RELIABILITY. MAXIMUM JUNCTION TEMPERATURE
IS 125oC.
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1401A
ADJUSTABLE SINGLE RESISTOR LDO REGULATOR
THERMAL IMAGE
An example thermal image shows the temperature distribution on board. The test is done in still air at room temperature with 2.0W power dissipation in LT3085.
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.
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1401A
ADJUSTABLE SINGLE RESISTOR LDO REGULATOR
5
Similar pages