Electronics Weekly
Its has a constant-frequency voltage-mode architecture, with its output voltage compared to an 800mV internal reference through a feedback pin. Input voltage feed-forward is implemented to improve line transient response.
100kHz – 1MHz switching and its 40ns minimum on-duration allows it to support extremely low duty-cycles and deliver 800mV to 60V.
The IC needs a pair of external n-channel mosfets to work, and includes a 7.5V supply (assuming enough input voltage) for the in-built gate drivers.
Diode emulation implements pulse skipping to maximise efficiency at light-load, although PWM mode can be forced to hold the switching frequency constant and minimise output voltage ripple.
Soft-start circuitry limits in-rush current during start-up, and a power good (Vout >87% of target) open-collector output is available for monitoring or to implement power-up voltage sequencing.
Protections include output over-current, input under-voltage lock-out and thermal shutdown. Hiccough circuitry handles over-load and short-circuit conditions.
Input over-voltage-lock-out is implemented through the enable pin, which has precision thresholds and controls three modes: shut-down, under-voltage idle and operating. “The central tap of a resistor divider connected to the pin from Vin designs the enable and under-voltage lockout thresholds”, said ST.
Packaging is 3.5 x 4.5mm 20pad QFN with wettable flanks.
ST foresees it being used in applications from industrial equipment to battery-powered light electric vehicles, as well as in telecom and networking equipment that have 24V or 48V buses.
STEVAL-L3751V12 is the associated 100W evaluation board (right) which is set to convert 6 – 75V into 5V (default 15A), although 12V out can be set with a jumper. Switching is at 230kHz, synch-able from 185 to 345kHz
The L3751 product page can be found here.
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