1
dc2469af
DEMO MANUAL DC2469A
DESCRIPTION
LT8603
42V, Low I
Q
, Quad Output Triple Monolithic
Buck Converter with Boost Channel as SEPIC
Demonstration circuit 2469A features the
triple monolithic buck regulators and the boost channel as
SEPIC. The demo circuit is designed for 8V, 5V, 3.3V, and
1.8V outputs from a nominal 12V input. The 4th channel is
set as a SEPIC converter and its output is regulated at 8V
over a wide input range. The two high voltage buck regula-
tors are powered from VOUT4. VOUT1 is regulated at 5V
with 1.5A maximum output load current, and VOUT2 is
at 3.3V with 2.5A maximum output load current. The low
voltage buck is powered from VOUT2 (3.3V), and the out-
put VOUT3 is regulated at 1.8V with 1.8A maximum load
current. Thanks to the SEPIC converter, all four outputs
can ride through a cold crank in automotive applications
while providing regulated output voltages.
All regulators are synchronized to an internal oscillator
that can be programmed with one resistor at RT pin.
Programmable frequency allows optimization between
efficiency and external component size. To avoid the audio
band, the DC2469A sets the switching frequency at 2MHz
for the three buck regulators, and the SEPIC converter is
at 400kHz. At all frequencies, a 180° phase shift is main-
tained between 1 and 2 channels, reducing the input peak
current and voltage ripple.
All registered trademarks and trademarks are the property of their respective owners.
PERFORMANCE SUMMARY
Many popular features such as soft-start, cycle-by-cycle
current limit, power good for each of the four channels
are packed in the 40-lead 6mm
×
6mm QFN package to
simplify the complex design of quad-output power con-
verters. Each buck regulator can be independently dis-
abled using its own TRKSS or RUN pin. The SEPIC can be
disabled by pulling down both the FSEL4A and FSEL4B.
The EN/UVLO can be used to shut down the circuit to
reduce the input current to 1µA.
Table 1 summarizes the performance of the demo board at
room temperature. The demo circuit can be easily modi-
fied for various automotive, transportation and industry
applications. For applications that need 4th channel con-
figured as a boost converter, the DC2114A should be used.
The LT8603 data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this quick start
guide for DC2469A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2469A
Specifications are at T
A
= 25°C
Table 1.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Operation Input Voltage Range
3
12
42
V
Minimum Start-Up, VIN
MIN
4.5
V
Standby Current When Switching
IOUT1,2,3,4 = 0mA, V
IN
= 12V
40
µA
Channel 4 Output Voltage, VOUT4
IOUT4 = 1A
7.68
8
8.32
V
Channel 1 Output Voltage, VOUT1
IOUT1 = 1.5A
4.86
5
5.14
V
Channel 2 Output Voltage, VOUT2
IOUT2 = 2.5A
3.17
3.3
3.43
V
Channel 3 Output Voltage, VOUT3
IOUT3 = 1.8A
1.73
1.8
1.87
V
Maximum Output Current, IOUT1
V
IN
= 12V
1.5
A
Maximum Output Current, IOUT2
V
IN
= 12V, IOUT3 = 0A
2.5
A
