QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 913
POLYPHASE 3-OUTPUT STEP-DOWN SUPPLY WITH TRACKING
LTC3773EUHF
DESCRIPTION
Demonstration circuit 913 is a high efficiency and
high density supply featuring the 3-output, 3-phase
synchronous buck regulator LTC3773. The input
voltage range of the demo board is designed for 4.5V
to 13.5V, though the LTC3773 controller can take up
to 36V
MAX
Vin. The outputs of this board are
2.5V/15A,1.8V/15A and 1.2V/15A. To minimize input
ripple current and capacitor size, there is 120
°
phase
clock interleaving among every two phases. The
power up/down tracking of the three output voltages
is programmable. The supply can be synchronized
to an external clock signal.
The critical power components are on the top side of
the PC board and are within a 1.7” x 1.7” “drop-in”
layout area. The small signal components and IC are
on the bottom side of the PC board within a 1” x 1”
board area. The LTC3773EUHF regulator IC is in a
small 5mm x 7mm QFN package with exposed ther-
mal pad for low thermal impedance. An optional 5V
bias supply is stuffed on the board to power the
LTC3773.
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 (T
A
= 25°C)
PARAMETER
Input Voltage
Output Voltage V
OUT1
Output Voltage V
OUT2
Output Voltage V
OUT3
Maximum Output Current
Switching frequency
Full Load Efficiency
CONDITION
Typical
I
OUT1
= 0A to 15A
I
OUT2
= 0A to 15A
I
OUT3
= 0A to 15A
VIN = 4.5V-13.5V
4.5V-13.5Vin
V
IN
= 12V, V
OUT1
= 2.5V, I
OUT1
= 15A
V
IN
= 12V, V
OUT2
= 1.8V, I
OUT2
= 15A
V
IN
= 12V, V
OUT3
= 1.2V, I
OUT3
= 15A
VALUE
4.5V-13.5V
2.5V ± 2%
1.8V ± 2%
1.2V ± 2%
15A Each Output
400kHz
90% Typical
88 % Typical
84.5 % Typical
(15V abs_max)
QUICK START PROCEDURE
Demonstration circuit 913 is easy to set up to evaluate the performance of the LTC3773EUHF. Refer to Figure 1
for proper measurement equipment setup and follow the procedure below:
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 913
POLYPHASE 3-OUTPUT STEP-DOWN SUPPLY WITH TRACKING
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.
The following are the default jumper settings:
+5V
Select
INT.
INT 5V
ON
PHASMD
120
SDB1
ON
SDB2
ON
SDB3
ON
FC
CCM
1.
The following tables show the assembly options to program the power up/down tracking among Vout1, Vout2
and Vout3:
VOUT1 TRACKING
OPTIONS
1
*
2
Softstart W/O tracking
Track TRACK1
R8
0
Stuff, value
TBD
C13
DNP
Stuff R,
value TBD
C10
0.01uF
DNP
VOUT2 TRACKING
OPTIONS
1
2*
Softstart W/O tracking
Track VOUT1
R13
DNP
20K
R18
DNP
10K
C22
0.01uF
DNP
VOUT3 TRACKING
OPTIONS
1
2*
Softstart W/O tracking
Track VOUT2
R28
DNP
10K
R30
DNP
10K
C29
0.01uF
DNP
*With existing tracking circuit assembly, VOUT1 starts independently (Option 1). VOUT2 tracks VOUT1 during
start up (option 2). VOUT3 tracks VOUT2 during start up (option 2). Figure 6 and 7 are the typical power-up/down
waveforms with rail tracking.
4.
2.
With power off, connect the input power supply to
VIN and GND. Connect the loads between VOUT1,
VOUT2, VOUT3 and GND. Preset the load current
at 0A (minimum). Refer to Figure 1 for correct test
set up.
Turn on the input power.
NOTE:
Make
5.
Check for the proper output voltages: V
OUT1
: 2.45V-
2.55V, V
OUT2
: 1.764V – 1.836V, and V
OUT3
: 1.176V –
1.224V
there is no output, temporarily disconnect
the load to make sure that the load is not set too
high.
Once the proper output voltages are established,
adjust the loads within the operating range and ob-
serve the output voltage regulation, ripple voltage,
efficiency and other parameters.
NOTE:
If
3.
sure that the input voltage does not ex-
ceed 15V.
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 913
POLYPHASE 3-OUTPUT STEP-DOWN SUPPLY WITH TRACKING
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
VIN
GND
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 913
POLYPHASE 3-OUTPUT STEP-DOWN SUPPLY WITH TRACKING
Vout 1=2.5V: Efficiency vs. Load Current
100.00
90.00
80.00
Efficiency (%)
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0.00
0
2
4
6
8
10
12
14
Load Current (A)
(Vin = 5V)
(Vin = 12V)
Figure 3. Typical Supply Efficiency vs Load Current of 2.5V output
Vout 2=1.8V: Efficiency vs. Load Current
100.00
90.00
80.00
Efficiency (%)
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0.00
0
2
4
6
8
Load Current (A)
10
12
14
16
Vin = 5V
Vin = 12V
Figure 4. Typical Supply Efficiency vs Load Current of 1.8V output
Vout3=1.2V: Efficiency vs. Load Current
100.00
90.00
80.00
Efficiency (%)
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0.00
0
2
4
6
8
10
12
14
Load Current (A)
Vin = 5V
Vin = 12V
Figure 5. Typical Supply Efficiency vs Load Current of 1.2V output
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 913
POLYPHASE 3-OUTPUT STEP-DOWN SUPPLY WITH TRACKING
Power Up
V
O1
V
O2
V
O3
V
IN
Figure 6. Power Up Tracking
Power Down
V
O1
V
O2
V
O3
Figure 7. Power Down Tracking
5
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