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dc2123bfa
DEMO MANUAL DC2123B
DESCRIPTION
LT3790
60V Four-Switch Synchronous
Buck-Boost Controller
The DC2123B is a 60V four-switch synchronous buck-boost
controller that demonstrates the high power capability
of the
LT
®
3790
. The output is 24V and the maximum
output current is 5A. The switching frequency is 200kHz
and efficiency is as high as 98% for a 24V input.
The LT3790 is capable of high power operation. DC2123B
can be altered for increased output power with higher
minimum input voltage. If V
IN
remains always above
20V, I
OUT
can be increased to 12A
+
(for 290W output) by
changing RS2 to 4mΩ.
The operating input voltage range of DC2123B is from 8V
to 56V. The output voltage, EN/UVLO, and OVLO are all
programmed by resistor dividers. EN/UVLO is set so the
circuit will turn off when the input voltage falls below 8V
and will turn on when the input voltage rises above 9.6V.
OVLO is set to engage for input voltages above 57V.
Current sense resistors program input and output current
limits and also determine the monitoring voltages that
indicate input and output current. IVINMON provides a
30mV/1A voltage that is used to monitor the input cur-
rent. Input current limit occurs at 33.3A and is set by
RIN1. ISMON provides a 160mV/1A voltage that is used
to monitor the output current. The output current limit is
7.5A and is set by RS2.
The demo circuit features MOSFETs that compliment the
5V gate drive of the LT3790 to achieve high efficiency. 60V
MOSFETs are used on the input side of the four-switch
topology while 40V MOSFETs are used on the output side.
Ceramic capacitors are used at both the circuit input and
output because of their small size and high ripple current
capability. In addition to ceramic capacitors, there is an
aluminum polymer capacitor on the output that assures
feedback loop stability, even at low temperatures. The
input has an aluminum electrolytic capacitor in addition
to ceramic capacitors. A two-stage L-C input filter can
easily be added for electro-magnetic compatibility. The
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.
pcb has large copper planes and extensive vias for thermal
performance.
The CLKOUT output and the SYNC input can be used to
synchronize switching between two or more DC2123B
circuits. A resistor from SYNC to ground must be removed
prior to using the SYNC input.
SHORT
and
C/10
are open-collector status flag outputs and
are pulled up to the INTV
CC
pin voltage. A resistor shorts
the CCM pin to
C/10
and causes the circuit to change to
discontinuous conduction mode (DCM) when
C/10
is active
at light load currents. CCM can also be connected with a
resistor to INTV
CC
instead of
C/10
for continuous conduc-
tion mode (CCM) operation over the entire load range.
The CTRL input is pulled up to the V
REF
pin through a 0Ω
resistor to set the output current limit to its maximum,
and an external voltage on CTRL can be used to lower the
current limit if the resistor is removed. A capacitor at the
SS pin programs soft-start and additionally SS is pulled
up to the V
REF
pin through a 100k resistor. The switching
frequency is adjustable with a resistor.
The demo circuit is designed to be easily reconfigured to
many other applications, including the example schemat-
ics in the data sheet. Consult the factory for assistance.
High power operation, four-switch buck-boost topology,
fault protection and full monitoring make the LT3790
attractive for high power voltage regulator circuits and
also circuits that require output current regulation such
as battery chargers. The LT3790EFE is available in a
thermally enhanced 38-lead TSSOP package. The LT3790
data sheet must be read in conjunction with this demo
manual to properly use or modify demo circuit DC2123B.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2123B
