DEMO MANUAL DC2009A
LT3791-1
60V Four-Switch Synchronous
Buck-Boost Controller
DESCRIPTION
Demonstration circuit 2009A is a 60V four-switch syn-
chronous buck-boost controller that demonstrates the
high power capability of the LT3791-1. 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 operating input voltage range of DC2009A is from
12V to 57V. 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
11.9V and will turn on when the input voltage rises above
13.4V. 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
60mV/1A voltage that is used to monitor the input cur-
rent. Input current limit occurs at 16.7A and is set by
RIN1. ISMON provides a 150mV/1A voltage that is used
to monitor the output current. The output current limit is
6.7A and is set by RS2.
The demo circuit features MOSFETs that compliment the
5V gate drive of the LT3791-1 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
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 DC2009A
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 100k
resistor to set the output current limit to its maximum,
and an external voltage on CTRL can be used to lower the
current limit. 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 LT3791-1
attractive for high power voltage regulator circuits and
also circuits that require output current regulation such
as battery chargers. The LT3791EFE-1 is available in a
thermally enhanced 38-lead TSSOP package. The LT3791-1
data sheet must be read in conjunction with this demo
manual to properly use or modify demo circuit DC2009A.
Design files for this circuit board are available at
http://www.linear.com/demo
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.
dc2009af
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DEMO MANUAL DC2009A
PERFORMANCE SUMMARY
PARAMETER
Minimum Input Voltage, V
PVIN
Maximum Input Voltage, V
PVIN
Maximum Output Current
Input EN Voltage, V
PVIN(EN)
Input UVLO Voltage, V
PVIN(UVLO)
Input OVLO Turn-Off Voltage, V
PVIN(OVLO turn-off)
Input OVLO Turn-On Voltage, V
PVIN(OVLO turn-on)
Output Voltage V
OUT
Efficiency
Switching Frequency
Input Current Limit
Output Current Limit
Specifications are at T
A
= 25°C
CONDITIONS
V
OUT
= 24V I
OUT
≤ 4.5A
V
OUT
= 24V I
OUT
≤ 4.5A
13.3V < V
PVIN
< 57V, CTRL = V
REF
V
PVIN
= 12V, CTRL = V
REF
R3 = 56.2k, R4 = 499k, V
PVIN
Rising
R3 = 56.2k, R4 = 499k, V
PVIN
Falling
R11 = 27.4k, R1 = 499k, V
PVIN
Rising
R11 = 27.4k, R1 = 499k, V
PVIN
Falling
R19 = 60.4k, R20 = 3.83k
V
PVIN
= 24V, I
OUT
= 5A
V
PVIN
= 12V, I
OUT
= 4.5A
R18 = 147k
RIN1 = 0.003Ω
RS2 = 0.015Ω
23.6
98
96
200
16.7
6.7
5
4.5
13.4
11.9
57.6
56.2
24.7
MIN
TYP
12
57
MAX
UNITS
V
V
A
A
V
V
V
V
V
%
%
kHz
A
A
QUICK START PROCEDURE
It is easy to set up demonstration circuit DC2009A to
evaluate the performance of the LT3791-1. Refer to figure
1 for the proper measurement equipment setup and follow
the procedure below:
NOTE: Make sure that the voltage applied to PV
IN
does
not exceed the absolute maximum voltage rating of 60V
for the LT3791-1.
1. Connect the EN/UVLO terminal to ground with a clip-on
lead. Connect the power supply (with power off), load,
and meters as shown.
2. After all connections are made, turn on the input power
and verify that the input voltage is between 14V and
57V.
3. Remove the clip-on lead from EN/UVLO. Verify that the
output voltage is 24V.
NOTE: If the output voltage is low, temporarily disconnect
the load to make sure that it is not set too high.
4. Once the proper output voltage is established, adjust
the input voltage and load within the operating ranges
and observe the output voltage regulation, ripple volt-
age, efficiency and other parameters.
dc2009af
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