DESCRIPTION
DEMO MANUAL DC2123B
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
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
20V, I
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
®
3790. The output is 24V and the maximum
remains always above
IN
can be increased to 12A+ (for 290W output) by
OUT
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
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
tion mode (CCM) operation over the entire load range.
The CTRL input is pulled up to the V
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
-
frequency is adjustable with a resistor.
The demo circuit is designed 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
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.
REF
instead of C/10 for continuous conduc-
CC
pin through a 100k resistor. The switching
pin voltage. A resistor shorts
CC
pin through a 0Ω
REF
be easily reconfigured to
-
dc2123bfa
1
DEMO MANUAL DC2123B
PERFORMANCE SUMMARY
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Input Voltage, V
Maximum Input Voltage, V
Maximum Output Current 8V < V
Input EN Voltage, V
Input UVLO Voltage, V
Input OVLO Turn-Off Voltage, V
Input OVLO Turn-On Voltage, V
Output Voltage V
Efficiency V
Switching Frequency R18 = 147k 200 kHz
Input Current Limit RIN1 = 0.0015Ω 33 A
Output Current Limit RS2 = 0.008Ω 7.5 A
OUT
PVIN
PVIN
PVIN(EN)
PVIN(UVLO)
PVIN(OVLO turn-off)
PVIN(OVLO turn-on)
Specifications are at TA = 25°C
V
= 24V I
OUT
V
= 24V I
OUT
PVIN
R3 = 88.7k, R4 = 499k, V
R3 = 88.7k, R4 = 499k, V
R11 = 27.4k, R1 = 499k, V
R11 = 27.4k, R1 = 499k, V
R19 = 71.5k, R34 = 1.37k, R20 = 3.83k 23.5 24.5 V
= 24V, I
PVIN
≤ 5A 8 V
OUT
≤ 5A 56 V
OUT
< 56V, CTRL = V
= 5A 98 %
OUT
REF
Rising 9.6 V
PVIN
Falling 8.0 V
PVIN
Rising 57.6 V
PVIN
Falling 56.2 V
PVIN
5 A
QUICK START PROCEDURE
It is easy to set up demonstration circuit DC2123B to
evaluate the performance of the LT3790. Refer to Figure1
for the proper measurement equipment setup and follow
the procedure below:
NOTE: Make sure that the voltage applied to PV
does
IN
not exceed the absolute maximum voltage rating of 60V
for the LT3790.
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 8V and56V.
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.
-
2
dc2123bfa
QUICK START PROCEDURE
VIN = 12V
VIN = 24V
LOAD CURRENT (A)
01234
5
80
85
90
95
100
EFFICIENCY (%)
dc2123 F02
DEMO MANUAL DC2123B
Figure 1. Proper Measurement Equipment Setup for DC2123B
Figure 2. Efficiency
dc2123bfa
3
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