DC1471A - Demo Manual

DEMO CIRCUIT 1471
LT3990
QUICK START
GUIDE
LT3990
62V, 350mA Step-Down Regulator with 2.5µA
Quiescent Current and Integrated Diodes
DESCRIPTION
Demonstration circuit 1471 is a monolithic stepdown DC/DC switching regulator featuring the
LT3990. The switching frequency is adjustable
up to 2.2MHz. The demo circuit is designed for
5V, 350mA output from a 6.5V to 62V input. The
wide input range of the LT3990 allows a variety
of input sources including automotive batteries
and 24V industrial supplies. Low ripple Burst
Mode increases the efficiency at the light load
while keeping the output ripple below 5mV in a
typical application. The part is in shutdown
when the EN pin is low and active when the pin
is high. The threshold of the EN pin is accurate
at 1V when Vin is above 4.2V. Adding a resistor
divider from Vin to EN can program the LT3990
to regulate the output only when Vin is above a
desired voltage.
Performance Summary (TA = 25oC)
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Output Voltage VOUT
Typical switching Frequency
Maximum Output Current
Typical efficiency
Typical output voltage Ripple
The catch diode and boost diode are integrated
to reduce the components count and solution
size. The circuit consumes only 2.5µA of quiescent current. The current mode control scheme
creates fast transient response and good loop
stability. The catch diode current is limited to
protect the part under short circuit and overvoltage conditions.
The LT3990 datasheet gives a complete description of the part, operation and application
information. The datasheet must be read in conjunction with this quick start guide for demo circuit 1471.
Design files for this circuit board are available. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
CONDITION
VIN=12V, Iout=350mA
VIN=12V, Iout=350mA
VALUE
6.5V
62V
5.04V ±3%
400kHz
350mA
83.27%
15mV
QUICK START PROCEDURE
Demonstration circuit 1471 is easy to set up to
evaluate the performance of the LT3990. Refer
to Figure 1 for proper measurement equipment
setup and follow the procedure below:
NOTE. When measuring the input or output voltage ripple, care
must be taken to avoid a long ground lead on the oscilloscope
probe. Measure the input or output voltage ripple by touching the
probe tip directly across the Vin or Vout and GND terminals. See
Figure 2 for proper scope probe technique.
1
LT3990
1.
2.
3.
Place JP1 on the ON position.
5.
With power off, connect the input
power supply to Vin and GND.
Turn on the power at the input.
Once the proper output voltage is
established, adjust the load within the
operating range and observe the output voltage regulation, ripple voltage,
efficiency and other parameters.
NOTE. Make sure that the input voltage does not exceed 62V.
4.
Check for the proper output voltage.
NOTE. If there is no output, temporarily disconnect the load to
make sure that the load is not set too high.
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
2
OFF
ON
EN/UVLO
PG
GND
E5
E6
E4
E3
VIN
6.5V - 62V
JP1
3
2
1
(Opt)
R8
VOUT
C4
10uF
100V
VIN
+
VIN
100K
0402
R6
C3
2.2uF
100V
1210
R7
(Opt)
3
5
7
10
12
15
4
14
6
NC
NC
NC
NC
NC
NC
EN/UVLO
PG
VIN
8
17
GND GND
U1
LT3990EMSE
RT
FB
FB
BD
BOOST
SW
16
1
2
13
11
9
R5
374K
1%
0402
(400kHz)
C2
0.22uF
16V
0603
L1
33uH
LPS6225-333ML
R2
316K
1%
R1
1.00M
1%
C5
22pF
C1
22uF
10V
1206
VOUT
E2
E1
GND
VOUT
5V / 350mA
LT3990
3
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