SGM6130 Datasheet, PDF (7/14 Pages) SG Micro Corp – Step-Down Converter

SGM6130
3A, 28.5V, 385kHz Step-Down Converter
OPERATION
Main Control Loop
The SGM6130 is current-mode step-down regulator. It
regulates input voltages from 4.5V to 28.5V down to an
output voltage as low as 0.8V, and is able to supply up to
3A of load current.
Soft-Start
The device includes a soft-start to limit the inrush current
and prevent the overshoot of output voltage. The
soft-start time can be programmed by the external
soft-start capacitor and it is calculated as:
The SGM6130 uses current-mode control to regulate the
output voltage. The output voltage is measured at FB
through a resistive voltage divider and amplified through
the internal error amplifier. The output current of the
transconductance error amplifier is presented at COMP
where a network compensates the regulation control
system. The voltage at COMP is compared to the switch
current measured internally to control the output voltage.
The converter uses an internal N-Channel MOSFET
switch to step-down the input voltage to the regulated
output voltage. A boost capacitor connected between SW
and BS drives the gate of MOSFET, and makes it greater
than input voltage while SW is high. Thus, the MOSFET
will be in low resistance conducting state. The capacitor
is internally charged while SW is low.
t_SS = 100kΩ × C_SS
For example, C_SS =0.1μF corresponds to a 10ms soft-
start time.
To get perfect power on start performance, right soft-start
time must be added to adjust the sequence between
power supply and the output voltage in order to
guarantee the self-boost capacitor is charged correctly.
Usually a 1μF C_SS is good enough, if the power supply is
decoupled by big input capacitor, a long soft-start time is
preferred.
An internal 10Ω switch from SW to GND is used to
ensure that SW is pulled to GND during shutdown to fully
charge the BS capacitor.
SG Micro Corp
7
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