DESCRIPTION
Demonstration circuit 2626A is a 4-switch synchronous
buck-boost regulator that demonstrates the high power
capability of the LT®8392. The output is 12V and the
maximum output current is 12A for up to 144W power
delivery. The switching frequency is 200kHz and efficiency
can exceed 97%.
The steady-state operating input voltage range of
DC2626A in which the temperature of the components is
less than 90°C is from 9V to 18V. The transient operating
input voltage range of DC2626A is from 3V to 36V.
The output voltage and EN/UVLO are all programmed by
resistor dividers. EN/UVLO is set so the circuit will turn
off when the input voltage falls below 3V and will turn on
when the input voltage rises above 4V. The PCB has large
copper planes and extensive vias for excellent high power
thermal performance.
DC2626A features MOSFETs that complement the 5V
gate drive of the LT8392 to achieve high efficiency. 40V
AEC-Q101 MOSFETs are used on the input and output
side of the four-switch topology. 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 are bulk aluminum polymer
capacitors on the input and output to make input and
output stable during transient period.
The CTRL input is pulled up to the VREF 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.
To improve the EMI performance, the LT8392 has spread
spectrum frequency modulation. With the SYNC/SPRD pin
tied to INTVCC, LT8392 spreads its switching frequency
±15% around the programmed oscillator frequency.
The PGOOD status flag indicates when output voltage is
within ±10% of the final regulation voltage.
The LT8392’s proprietary peak current mode buck-boost
architecture ensures DC2626A runs either in discontinuous
conduction mode (DCM) or pulse-skipping mode
(PSM) without reverse inductor current. Both modes
enhance the light load efficiency.
The demo circuit is designed to be easily reconfigured to
suit other applications, including the example schematics
in the data sheet. Consult the factory for assistance.
High power operation, 3V input voltage operation,
4-switch buck-boost topology, proprietary peak current
mode architecture, fault protection and output current
monitoring make the LT8392 attractive for high power
voltage regulator circuits and also circuits whose input
voltage drops to 3V such as cold crank of car battery. It
is also suitable for output current regulation such as battery
chargers. The LT8392JFE is available in a thermally
enhanced 28 lead TSSOP package. The LT8392 data sheet
must be read in conjunction with this demo manual to
properly use or modify demo circuit DC2626A.