DC1290A - Demo Manual

DEMO CIRCUIT 1290A
LTC3775EUD
QUICK START
GUIDE
LTC3775EUD
HIGH FREQUENCY SYNCHRONOUS STEP-DOWN CONVERTER
DESCRIPTION
Demonstration circuit 1290A is a high frequency synchronous step-down converter featuring the
LTC3775EUD. The circuit is designed as a drop-in layout
with the main circuit components fitting in a 1” by ½”
area. The package style for the LTC3775EUD is a 16-pin
3mm x 3mm QFN.
Two versions of the demonstration board are available.
DC-1290A-A has been optimized for 5V to 26V input,
while the DC1290A-B is optimized for 5V to 36Vin range.
Both circuits are designed for minimal size and maximum step-down ratio to demonstrate the low on-time
capability of the LTC3775EUD and not for maximum efficiency.
The main features of the board include an internal 5V
linear regulator for bias and a Mode selector that allows
the converter to run in forced continuous conduction
(FCC) or pulse skip mode operation. Synchronization to
an external clock is also possible.
The LTC3775 datasheet gives a complete description of
the part, operation and application information and must
be read in conjunction with this quick start guide for
demo circuit 1290A
Design files for this circuit board are available. Call
the LTC factory.
L, LTC are registered trademarks of Linear Technology Corporation. Other product names
may be trademarks of the companies that manufacture the products.
PERFORMANCE SUMMARY Specifications are at TA = 25°C
SYMBOL
VIN
PARAMETER
Input Supply Range
VOUT
Output Voltage Range
IOUT
Maximum Load Current
fSW
Typical Free Running Switching Frequency
Efficiency
See Figures 3 and 4 for efficiency curves
CONDITIONS
DC1290A-A
DC1290A-B
VIN = 5-26V, (DC1290A-A)
VIN = 5-36V (DC1290A-B)
DC1290A-A
DC1290A-B
DC1290A-A
DC1290A-B
DC1290A-A, VIN = 12V, IOUT = 15A
DC1290A-B , VIN = 12V, IOUT = 10A
MIN
5
5
TYP
MAX
26
36
UNITS
V
1.164
1.20
1.236
V
15
10
500
330
85.5
86.5
A
A
kHz
kHz
%
%
QUICK START PROCEDURE
Demonstration circuit 1290A is easy to set up to evaluate
the performance of the LTC3775EUD. 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 or directly across relevant capacitor.
See Figure 2 for proper scope probe technique.
1. Place jumpers in the following positions:
JP1 FCC
JP2 ON
2. With power off, connect the input power supply to
Vin and GND.
1
LTC3775EUD
3. Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed 26V or 36V for
DC1290A–A or DC1290A–B demonstration boards respectively.
4. Check for the proper output voltages.
VOUT = 1.164V to 1.236V
If there is no output, temporarily disconnect the load
to make sure that the load is not set too high.
5. Once the proper output voltage is established, adjust
the loads within the operating range and observe the
output voltage regulation, ripple voltage, efficiency
and other parameters.
A
+
V
-
+
A
IOUT
IIN
Vin supply
+
Load
Vin
-
-
+
V
-
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple Across Terminals or Directly Across Bulk Capacitor
FREQUENCY SYNCHRONIZATION AND MODE SELECTION
Demonstration circuit 1290A’s Mode selector allows
the converter to run in FCC operation, pulse skip operation or synchronizing to an external clock by changing
2
the position of JP1 accordingly. Please note that the
external synchronizing frequency should be close to
(+/-20%) the free running frequency.
LTC3775EUD
Mode Selection and Synchronized Operation Options
CONFIGURATION
FCC operation
Pulse skip operation
Synchronized to ext. clock applied to SYNC pin
JP1
‘FCC’
‘Pulse_Skip’
‘Sync’
Figure 3. Typical Efficiency vs. Load Current for DC1290A-A
Figure 4. Typical Efficiency vs. Load Current for DC1290A-B
3
LTC3775EUD
Top
Bottom
Figure 5. Thermal images of DC1290A-A, 26VIN, 1.2VOUT @ 15A, 22°C ambient
Top
Bottom
Figure 6. Thermal images of DC1290A-B, 36VIN, 1.2VOUT @ 10A, 22°C ambient
4
LTC3775EUD
5
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