DEMO MANUAL DC2236A-B
LTC3890
60V, Low I
Q
Multiphase Synchronous
Step-Down Converter
DESCRIPTION
Demonstration circuit 2236A-B is a high output voltage,
high efficiency synchronous PolyPhase
®
buck converter
featuring the
LTC
®
3890EUH.
The DC2236A-B has wide
input voltage range of 16V up to 60V, and is capable of
delivering up to 25A of output current. The output voltage
is set to 12V, however, the output voltage can go as high
as 24V, with certain modifications. The DC2236A-B sup-
ports three operation modes: Fixed frequency modulation,
pulse-skipping and Burst Mode
®
operation. Fixed frequency
mode of operation maximizes the output current, reduces
output voltage ripple, and yields a low noise switching
spectrum. Burst Mode employs a variable frequency
switching algorithm that minimizes the no-load input
quiescent current and improves efficiency at light loads.
The DC2236A-B consumes less than 50µA of quiescent
current during shutdown and less than 1mA under a no
load condition with the output in regulation in Burst Mode
operation. The DC2236A-B has a standard operating
frequency of 150kHz, but can be adjusted to frequencies
as high as 900kHz. The DC2236A is a dual phase single
output step-down converter; however it designed to be
easily transformed to 4- or 6-phase system by combin-
ing two or three DC2236A-B boards. The LTC3890EUH
data sheet gives a complete description of these parts,
operation and application information and must be read
in conjunction with this quick start guide for demonstra-
tion circuit 2236A-B. Table 1 summarizes the differences
between the parts in the LTC3890 family.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2236A-B
L,
LT, LTC, LTM, Linear Technology, Burst Mode, PolyPhase and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
PERFORMANCE SUMMARY
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Output Voltage V
OUT
Regulation
Maximum Continuous Output Current
Preset Operating Frequency
External Clock Sync. Frequency Range
Efficiency
Typical Output Ripple V
OUT
Quiescent Current at Shutdown
Input Current at No Load
Specifications are at T
A
= 25°C
CONDITIONS
VALUE
16V
60V
V
IN
= 16V to 55V
R7 = 30.1kΩ
V
IN
= 36V, V
OUT
= 12V, I
OUT
= 12A, See Figure 3 Efficiency Curves for
Complete Operating Range
V
IN
= 36V, I
OUT
= 12A (20MHz BW)
V
IN
= 16V to 55V
V
IN
= 16V to 55V
12V ± 2%
25A
150kHz
75kHz to 850kHz
97%
<35mV
P-P
<50µA
<1mA
dc2236abf
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DEMO MANUAL DC2236A-B
QUICK START PROCEDURE
Demonstration circuit 2236A-B is easy to set up to evaluate
the performance of the LTC3890. For proper measurement
equipment configuration, set up the circuit according to
the diagram in Figure 1. Before proceeding to test, insert
shunt into JP1 (RUN) OFF position, which connects the
RUN pin to ground (GND), and thus, shuts down the circuit.
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 V
IN
or
V
OUT
and GND terminals. See Figure 2 for proper scope
probe technique.
1. With the DC2236A-B set up according to the proper
measurement and equipment in Figure 1, apply 20V at
V
IN
. Measure V
OUT
; it should read 0V. If desired, one
can measure the shutdown supply current at this point.
The supply current will be approximately 50µA, or less,
in shutdown.
2. Turn on the circuit by inserting the shunt in header JP1
(RUN) into the ON position. The output voltage should
be regulating. Measure V
OUT
– it should measure 12V
± 2%
(Do not apply more than the rated maximum
voltage of 60V to the board or the part may be dam-
aged).
3. Vary the converter load, which should not exceed 25A.
Note: all four input and output terminals VIN, VOUT and
two GND equipped with two banana connectors, two-
wires can be used for each terminal to reduce copper
looses and heat dissipation in the interconnection lines.
4. Vary the input voltage from 16V to 55V, the V
OUT
– it
should measure 12V ± 2%
5. Set output current to zero and move jumper JP2 (MODE)
into BURST MODE position and measure V
OUT
– it
should register 12V ± 2%.
6. Set output current to zero and move jumper JP2 (MODE)
into PLS SKIP position and measure V
OUT
– it should
register 12V ± 2%
Figure 1. Proper Measurement Equipment Setup
dc2236abf
2
DEMO MANUAL DC2236A-B
QUICK START PROCEDURE
Table 1. Summary of the Differences Between the Parts in the LTC3890 Family
LTC3890
I
LIM
Pin for Adjustable
Current Sense Voltage?
CLKOUT and PHASMD Pins
for PolyPhase
®
Operation?
Independent PGOOD Pins for
Each Channel
Overvoltage Protection
Bottom Gate “Crowbar?”
Current Foldback During
Overcurrent Events
Light Load Operation When
Synchronized to External
Clock Using PLLIN/MODE Pin
SENSE Pins Common Mode
Range
Yes
Yes
Yes; PGOOD1 and PGOOD2
Yes
Yes
Forced Continuous
LTC3890-1
No
No
No; PGOOD1 Only
Yes
Yes
Forced Continuous
LTC3890-2
Yes
Yes
Yes; PGOOD1 and PGOOD2
No; BG Not Forced On
No
Pulse-Skipping
LTC3890-3
No
No
No; PGOOD1 Only
No; BG Not Forced On
No
Pulse-Skipping
Operation with SENSE
Common Mode < 0.5V
Requires V
FB
< 0.65V
Operation with SENSE
Common Mode < 0.5V
Requires V
FB
< 0.65V
Not Dependent on V
FB
Voltage. Makes It Easy to
Make a Non-synchronous
Boost or SEPIC Converter
with Ground-Referenced
Current Sensing
Not Dependent on V
FB
Voltage. Makes It Easy to
Make a Non-synchronous
Boost or SEPIC Converter
with Ground-Referenced
Current Sensing
dc2236abf
3
DEMO MANUAL DC2236A-B
QUICK START PROCEDURE
Figure 2. Measuring Input or Output Ripple
VIN
99.5
99.0
98.5
η
(%)
98.0
97.5
97.0
96.5
96.0
5
0.22
0.20
0.18
I
IN
(mA)
0.16
0.14
0.12
0.10
20
25
10
Figure 3. Efficiency vs Load
Figure 4. Input Current at No Load vs Input Voltage (Burst Mode)
GND
24V
36V
48V
20
15
LOAD (A)
25
30
dc2236ab F03
30
35
V
IN
(V)
40
45
50
dc2236ab F04
dc2236abf
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DEMO MANUAL DC2236A-B
QUICK START PROCEDURE
Figure 5. Output Noise, V
IN
36V, I
O
12A
Figure 6. Thermal Map, V
IN
48V, V
O
12V, I
O
25A, No Air Flow
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