Kontron MARS Smart Battery Kit - Manual (Page 20)

MARS User´s Guide
8. Dual Buck Converter
(Abbr.: DB)
The dual buck converter is used, to generate the 12V and 5V at the output of SBS MARS, to source
the system. It must be able to convert the high battery voltages to 12V and 5V.
The LTC3727 from Linear Technologies is used in the SBS MARS for this function.
The characteristics of the IC are:
• Out-of-phase controllers reduce required input capacitance and power
supply induced noise
• OPTI-LOOP® compensation minimizes C
OUT
• Phase-lockable fixed frequency 250kHz to 550kHz
• ±1% output voltage accuracy
• Output overvoltage protection
The LTC3727 is a high performance dual step-down switching regulator controller that drives all N-
channel synchronous power MOSFET stages. A constant frequency current mode architecture allows
phaselockable frequency of up to 550kHz. Power loss and noise due to the ESR of the input
capacitors are minimized by operating the two controller output stages out of phase.
OPTI-LOOP compensation allows the transient response to be optimized over a wide range of
output capacitance and ESR values. There is a precision 0.8V reference and a power good output
indicator. A wide 4V to 30V (36V maximum) input supply range encompasses all battery
chemistries.
This converter also has the option to control the output current of both paths. For this reason it is
possible to increase the safety of the system.
8.1 Possible Configurations
8.1.1 Adjustment of the frequency
A 0Ω resistor controls the frequency of the dual buck converter. A populated R48 switch the
freqnency to 530 kHz, a populated R49 to 255 kHz.
If lower power is necessary and a different dimensioning of the converter must be done the lower
frequency has an advantage. The converter gets more efficient and the radiation (EMR) will
decrease.
8.2 Dual buck converter without 12V path
8.2.1 Basic Conditions
If the battery voltage can drop below 12V it must be sourced by the output buck-boost converter
and the 12V path of the dual buck converter is obsolete.
Dual Buck Converter
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