DEMO MANUAL DC1755A
LTC3860EUH
Wide Input Range,
High Efficiency Step-Down
DC/DC Converter
The main features of the board are listed below:
• High efficiency and high current density.
• Remote sensing for each output.
• Optional resistors to tie the two outputs together.
• Connector and header to tie two or more boards together
for up to 12-phase operation.
• RUN, PGOOD and TRACK/SS pins for each output.
• CLKIN and CLKOUT pins.
• Onboard bias voltage regulator.
• BNC connectors to monitor each output voltage.
Design files for this circuit board are available at
http://www.linear.com/demo
DESCRIPTION
Demonstration circuit DC1755A provides the user with
two high current dual phase synchronous buck converters
driven by the LTC3860. These buck converters provide
outputs of 1.5V/50A and 1.2V/50A over an input voltage
range of 6V to 14V and a switching frequency of 500kHz.
The board can be easily modified for a 4-phase, single V
O
,
100A supply. The power stage for each phase consists
of the tri-state PWM compatible 6mm × 6mm Fairchild
DrMOS module and a 0.47μH 13.2mm × 12.8mm iron
powder type inductor from Würth. A high density, two
sided drop-in layout is used. The entire converter, excluding
the bulk output and input capacitors, fits within a 2.25” ×
1.38” area on the board.
L,
LT, LTC, LTM, Linear Technology 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
OUTA
Output Voltage V
OUTB
V
OUTA
Maximum Output Current, I
OUTA
V
OUTB
Maximum Output Current, I
OUTB
Nominal Switching Frequency
Efficiency
See Figures 2 and 3
(T
A
= 25°C), no airflow.
VALUE
6V
14V
CONDITIONS
I
OUTA
= 0A to 50A, V
IN
= 6V to 14V
I
OUTB
= 0A to 50A, V
IN
= 6V to 14V
V
IN
= 6V to 14V, V
OUTA
= 1.5V
V
IN
= 6V to 14V, V
OUTB
= 1.2V
V
OUTA
= 1.5V, I
OUTA
= 50A, V
IN
= 12V
V
OUTB
= 1.2V, I
OUTB
= 50A, V
IN
= 12V
1.5V ± 2%
1.2V ± 2%
50A
50A
500kHz
90.2% Typical
89.2% Typical
dc1755af
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DEMO MANUAL DC1755A
QUICK START PROCEDURE
Demonstration circuit 1755A is easy to set up to evalu-
ate the performance of the LTC3860EUH. Please refer to
Figure 1 for proper measurement equipment setup and
follow the procedure below.
1) With power off, connect the input supply, load and
meters as shown in Figure 1. Preset the load to 0A and
V
IN
supply to be 0V. Place jumpers in the following
positions:
JP1
JP2
JP3
RUNA
RUNB
INT PWR BLK BIAS
ON
ON
ON
Note 3. Do not apply the load from the VOSA
+
turret to
the VOSA
–
turret or from the VOSB
+
turret to the VOSB
–
turret. These turrets are only intended to monitor the
voltage across COUT3 and COUT13 respectively. Heavy
load currents applied across these turrets may damage
the converter.
DYNAMIC LOAD CIRCUIT (OPTIONAL)
Demonstration circuit 1755A provides a simple load step
circuit consisting of a MOSFET and sense resistor for each
rail. To apply a load step, follow the steps below.
1) Preset the amplitude of a pulse generator to 0.0V and
the duty cycle to 5% or less.
2) Connect the scope to the VOUT BNC connectors for
the rail under test with a coax cable. To monitor the
load step current, connect the scope probe across the
ISTEP
+–
turrets for that rail.
3) Connect the output of the pulse generator to the PULSE
GEN turret for the rail under test and connect the return
to one of the GND turrets.
4) With the converter running, slowly increase the
amplitude of the pulse generator output to provide the
desired load step pulse height. The scaling for the load
step signal is 10mV/A.
2) Adjust the input voltage to be between 6V to 14V. V
OUTA
should 1.5V ± 2%.
V
OUTB
should 1.2V ± 2%.
3) Next, apply 50A load to each output and remeasure
V
OUT
.
4) Once the DC regulation is confirmed, observe the output
voltage ripple, load step response, efficiency and other
parameters.
Note 1. No airflow is required at room temperature with
50A on both outputs. But for ambient temperatures higher
than 30°C, a cooling fan is recommended.
Note 2. Use the BNC connectors labeled V
OUTA
or V
OUTB
to measure the output voltage ripple.
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DEMO MANUAL DC1755A
QUICK START PROCEDURE
+
I
OUTA
A
V
OUTA
load
-
-
V
OUTB
load
+
I
OUTB
A
+
V
OUTA
V
+
V
*
V
OUTB
-
-
*
+
V
V
IN
-
DC1755a F01
I
IN
A
+
V
IN
supply
-
*
Monitor voltage across COUT7
and COUT19 for accurate
efficiency measurements.
Figure 1. Proper Measurement Equipment Setup
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DEMO MANUAL DC1755A
QUICK START PROCEDURE
95
95
90
EFFICIENCY (%)
EFFICIENCY (%)
V
IN
= 6V
V
IN
= 10V
V
IN
= 12V
V
IN
= 14V
0
10
20
30
LOAD CURRENT (A)
DC1755a F02
90
85
85
80
80
75
40
75
60
0
10
20
30
LOAD CURRENT (A)
40
V
IN
= 6V
V
IN
= 10V
V
IN
= 12V
V
IN
= 14V
50
60
DC1755a F03
50
Figure 2. Efficiency Curves for the 1.5V Rail of the DC1755A
Figure 3. Efficiency Curves for the 1.2V Rail of the DC1755A
1.5V
O
(AC)
50mV/DIV
77mV
1.2V
O
(AC)
50mV/DIV
81mV
50A
50A
LOAD STEP
10A/DIV
25A
LOAD STEP
10A/DIV
25A
20μs/DIV
DC1755a F04
20μs/DIV
DC1755a F05
Figure 4. Load Step Response of the 1.5V Rail
Figure 5. Load Step Response of the 1.2V Rail
SINGLE OUTPUT/4-PHASE OPERATION
A single output/4-phase converter may be preferred for
higher output current applications. The optional compo-
nents required to tie the phases together are found on
sheet 3 of the schematic in the lower right hand corner. To tie
the two outputs together, make the following modifications:
1) Select one rail to be the master.
a) If VOUTA is the master, then stuff 0Ω at R103 to
disable the error amplifier for VOUTB.
b) If VOUTB is the master, then stuff 0Ω at R104 to
disable the error amplifier for VOUTA.
2) Stuff 0Ω at R87, R88, R89 and R91 to tie the IAVG,
COMP TRACK/SS and RUN signals together.
,
3) Remove the redundant compensation components.
6-PHASE AND 12-PHASE OPERATION
Two or more boards may be tied together for up to 12-phase
operation. To parallel two or more boards, place the boards
side by side. Connect J9 of one board to J10 of the ad-
jacent board (see sheet 3 of the schematic, lower right
hand corner). This will tie the IAVG, COMP TRACK/SS and
,
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DEMO MANUAL DC1755A
QUICK START PROCEDURE
RUN signals of the adjacent boards together. Next, locate
the exposed copper shapes on the four corners of the
board on the top and bottom layers. Use these shapes to
tie the VOUT, VIN and GND planes of the adjacent boards.
Next, select which phases will be the master or the slave.
6 PHASE
CONVERTER
Figure 6 shows the typical setup for a 6-phase + 2-phase
converter. Figure 7 shows the typical setup for a 12-phase
converter. For additional help and support, contact your
local LTC sales office.
TOP
Cu
Cu
BOARD #1
BOARD #1 = MASTER
R87, R88, R89, R91 = 0
R101, R102 = 0.0m
R103 = 0
R104 = NOT STUFFED
BOARD #2
BOARD #2
SIDE A = SLAVE
SIDE B = INDEPENDENT DUAL PHASE RAIL
R87, R88, R89, R91 = NOT STUFFED
R101, R102 = NOT STUFFED
R103 = NOT STUFFED
R104 = 0
6 PHASE
CONVERTER
2 PHASE
CONVERTER
BOTTOM
BOARD #2
GND
Cu
BOARD #1
GND
Cu
DC1755a F06
Figure 6. Typical Setup for a 6-Phase + 2-Phase Converter
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