Analog Devices DC2896A-B Demo Manual

DESCRIPTION
Demonstration circuit 2896A-B demonstrates a high
power boost converter and features the
phase expander with internal gate drivers. The DC2896A-B
employs LTC3769, a single-phase boost controller as pri-
mary controller and LT8551 as the phase expander which
added four more power phases. The increased number
of power sections connected to the LT8551, results in
greater higher level output power without a correspond-
ing increase in the difficulty of the design or a sacrifice of
primary controller LTC3769 features.
The input voltage range of DC2896A-B is from 10V to
46V and the output is 48V. The maximum input current is
12A per power section, so the maximum input current of
DC2896A-B is 60A. It's reflected to 30A of output current
and output power of 1,440W at an input voltage of 24V.
Correspondingly output current will drop to 14.5A and
output power will to 720W at a 12V input voltage, to keep
the input current at the same level of 60A. Both values
will increase at higher voltages. The input current value
can be increased above 60A, if heat sinks are installed,
see parts list below.
The switching frequency is 250kHz and at a 24V input
to 48V at full load, the efficiency of DC2896A-B is
OUT
98%. As the input voltage decreases, the output current
should be decreased as well, to prevent saturation of the
DC2896A-B inductors, the derating curve presented on
Figure 3. Efficiency curves presented on Figure 4.
DC2896A-B resistors R114 to R119 program the phase
relationship between the power sections, by setting the
Total Distinct Phase Number (TDPN). For increasing
efficiency and reducing switching losses at light loads
DC2896A-B supports disconnecting some power sec-
tions. This mode of operation designated as the stage
shedding and it is programed by the jumper J3 STAGE
SHED. Jumper JP1 programs the LT8551 SYNC pin and
it allows DC2896A-B to be synchronized to an external
clock. The print circuit board of DC2896A also supports
DEMO MANUAL DC2896A-B
High Power Boost Converter Based
on the Phase Expander
two phase expander controllers, the
LT 8551 the with versions DC2896A-A and DC2896A-B correspond-
®
ingly. The table [1] in the electrical schematic describes
differences between both versions, including controller
biasing and gate drive voltages.
DC2896A-B has jumper SHDN (JP2) for manually enable
or disable controller. The SYNC (E19) input can be used to
sync LT8551 with an external signal. There are also termi-
nals that make it easy to monitor the control logic of the
LT8551 functional. The current sense resistors R
R used for implementation of current mode control,
SNS5
monitoring and sharing current between the phases. To
further increase efficiency DC2896A-B supports optional
DCR sensing of inductors L1 to L5
DC2896A-B includes sense line filters and filter options
for inputs to the LT8551 in accordance with data sheet
recommendations. Undervoltage shutdown, switching
frequency and LT8551 ILIM current limit levels can all
be adjusted by resistors or resistor jumpers. DC2896A-B
comes with a housekeeping circuit based on U3 control-
ler. It reduces the power dissipation that would otherwise
occur at high input voltages in regulator transistor Q21.
The housekeeping circuit also stabilizes converter biasing
at sudden input voltage drops.
A high level of available output power without a cor-
responding high level of design complexity makes the
LT8551 attractive for high power DC bus and battery
systems in commercial, industrial and automotive set-
tings. DC2896A-B features the LT8551EUKG in a ther-
mally enhanced 52-pin 7mm × 8mm QFN package. The
LT8551 and LTC3769 data sheets must be read in con-
junction with this demo manual to properly use or modify
DC2896A-B.
Design files for this circuit board are
All registered trademarks and trademarks are the property of their respective owners.
LT8551
LT8561 and LT8551,
to
SNS1
available.
Rev. 0
1