QUICK START GUIDE FOR DEMONSTRATION CIRCUITS 1086/7A
DUAL SYNCHRONOUS, CONFIGURABLE, HIGH SWITCHING FREQUENCY BUCK REGULATORS
LTC3546EUFD
DESCRIPTION
Demonstration circuits 1086/7A are dual synchronous,
configurable, high switching frequency buck regulators
featuring the LTC3546EUFD. The two different demon-
stration circuits show the current partitioning capability
of the LTC3546EUFD to create either two 2A outputs
(DC1086A) or one 3A and one 1A output (DC1087A),
just by changing a single pin connection.
The main features of the board are separate RUN, soft
start and PGOOD pins for each output and a Mode selec-
tor that allow the converter to run in CCM, DCM or Burst
Mode operation. Synchronization to an external clock is
also possible through some minor component changes.
Both boards have an input voltage range of 2.5V to 5.5V.
In Burst Mode operation, the DC supply current is typi-
Table 1. Performance Summary (T
A
= 25°C)
PARAMETER
CONDITION
Vout1
Input Voltage Range
Maximum Output Current
Output Voltage
Nominal Switching Frequency
Typical Efficiency
V
IN
= 2.5V to 5.5V
V
IN
= 2.8V to 5.5V, I
OUT
= 0A to max. load
R
T
= 143kΩ
V
IN
= 5V, I
OUT
= Full load
V
IN
= 3.3V, I
OUT
= Full load
See Figures 3 – 6
V
IN
= 2.5V, I
OUT
= Full load
87%
86%
*
*
79%
*
83%*
2A
2.5V ±2%
2A
1.8V ±2%
DC1086A
Vout2
Vout1
DC1087A
Vout2
cally only 240µA at no load, and less than 1µA in shut-
down. The entire circuit, including the output capacitors,
fit within a 0.95” X 0.6” area on the top layer and is only
1.2mm high. The package style for the LTC3456EUFD is
a 4mm x 5mm plastic QFN.
The LTC3546EUFD datasheet gives a complete descrip-
tion of the part, operation and application information
and must be read in conjunction with this quick start
guide for demo circuits 1086/7A.
Design files for this circuit board are available. Call
the LTC factory.
Burst Mode is a trademark of Linear Technology Corporation
2.5V – 5.5V
1A
2.5V ±2%
3A
1.2V ±2%
1500kHz
87%*
87%
*
74%
*
77%*
*Up to 2% higher efficiency is possible with alternative higher profile inductors – see Table 2
OPERATING PRINCIPLES
A unique feature of the LTC3546EUFD is the flexible cur-
rent partitioning. The LTC3546EUFD has two independ-
ently regulated outputs that can deliver up to 2A and 1A
due to the 90mΩ and 180mΩ internal power MOSFET
switches. An additional 1A output, with 180mΩ internal
power MOSFET switches, can be paralleled to either of
the outputs to produce either a 3A/1A or a 2A/2A dual
output regulator. This external connection is internally
detected and the dependent output is automatically
gated in accordance to the connected output — nothing
more is required.
QUICK START PROCEDURE
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QUICK START GUIDE FOR DEMONSTRATION CIRCUITS 1086/7A
DUAL SYNCHRONOUS, CONFIGURABLE, HIGH SWITCHING FREQUENCY BUCK REGULATORS
Demonstration circuits 1086/7A are easy to set up to
evaluate the performance of the LTC3546EUFD. Refer to
0 for proper measurement equipment setup and follow
the procedure below:
measuring the input or output voltage rip-
ple, 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 input or output ceramic capacitors. See Figure 2 for
proper scope probe technique.
1.
NOTE:
When
3.
Turn on the power at the input.
NOTE:
Make
sure that the input voltage does not ex-
ceed 5.5V.
4.
Check for the proper output voltages.
V
OUT1
= 2.450V to 2.550V (Both DC1086/7A)
V
OUT2
= 1.764V to 1.836V (DC1086A)
V
OUT2
= 1.176V to 1.224V (DC1087A)
NOTE:
If
Place jumpers in the following positions:
JP1
JP3
JP5
CCM
SS1
ON
JP2
JP4
JP6
SS2
ON
180°
5.
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, ad-
just the loads within the operating range and observe
the output voltage regulation, ripple voltage, efficiency
and other parameters.
2.
With power off, connect the input power supply to V
IN
and GND.
Figure 1. Proper Measurement Equipment Setup
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUITS 1086/7A
DUAL SYNCHRONOUS, CONFIGURABLE, HIGH SWITCHING FREQUENCY BUCK REGULATORS
Figure 2. Measuring Input or Output Ripple Directly Across Ceramic Capacitor
OPTIONS
The demonstration circuits 1086/7 are optimized for
low profile with a maximum component height of
1.2mm. This height limitation affects the inductor se-
lection and can limit the circuit efficiency. If a higher
Table 2. Alternative inductor selections for improved efficiency
DC1086A
MANUFACTURER
Würth Electronik - PD2-MS Series
Cooper Bussmann – SDxx Series
Sumida – CDRH4D29LD Series
V
OUT1
1.2 µH
SD20 -
1.2 µH
1.5 µH
V
OUT2
1.2 µH
SD20 - 1.2
µH
1.5 µH
V
OUT1
0.56 µH
SD25 -
0.47 µH
0.8 µH
DC1087A
V
OUT2
1.7 µH
SD12 -
1.5 µH
2.2 µH
COMMENTS
5mm x 6mm x 2mm high
5.2mm x 5.2mm,
determined by series
height
efficiency is required and the height limitation can be
relaxed, alternative inductors can be selected. In the
list of a few alternative components to improve overall
efficiency is given in Table 2.
4.9mm x 4.9mm x 3mm high
FREQUENCY SYNCHRONIZATION
Demonstration circuits 1086/7A’s Mode selector al-
lows the converter to run in CCM, DCM or Burst Mode
operation by changing position of jumper JP1. For
synchronizing to an external clock source, however,
Table 3. Free Running and Synchronized Operation Options
FREQ PIN COMPONENTS
CONFIGURATION
Free Running
Synchronized to External Clock
R13
143kΩ
100pF
R26
0Ω
200kΩ
MODE SELECTOR
JP1
CCM, DCM or Burst Mode
CCM and clock applied to Sync/Mode pin
some bench modification is needed. Refer to Table 3
and to the data sheet for more details. Please note that
the LTC3546EUFD will operate in DCM mode when
synchronized to an external clock.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUITS 1086/7A
DUAL SYNCHRONOUS, CONFIGURABLE, HIGH SWITCHING FREQUENCY BUCK REGULATORS
BM
DCM
FCC
Figure 3. Efficiency vs. load current for different operating modes, DC1086A, V
IN
= 3.3V, V
OUT1
= 2.5V
BM
DCM
FCC
Figure 4. Efficiency vs. load current for different operating modes, DC1086A, V
IN
= 2.5V, V
OUT2
= 1.8V
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QUICK START GUIDE FOR DEMONSTRATION CIRCUITS 1086/7A
DUAL SYNCHRONOUS, CONFIGURABLE, HIGH SWITCHING FREQUENCY BUCK REGULATORS
BM
DCM
FCC
Figure 5. Efficiency vs. load current for different operating modes, DC1087A, V
IN
= 3.3V, V
OUT1
= 2.5V
BM
DCM
FCC
Figure 6. Efficiency vs. load current for different operating modes, DC1087A, V
IN
= 2.5V, V
OUT2
= 1.2V
TRACKING BETWEEN CHANNELS
It is possible to have either of the two output channels
act as master to the other channel during startup. In
this configuration, the other channel will either ramp
coincidental to the master (if it is a lower output volt-
age), or ramp in a similarly scaled manner. For Dem-
onstration Circuits 1086/7A this is accomplished by
tying the output of the Master channel to the Track pin
of the opposite channel, and changing the appropriate
jumper (JP2 or JP3) to the track position. Please refer
to Table 4 and the datasheet for more detail.
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