TPS54541_15 Datasheet, PDF (12/52 Pages) Texas Instruments – TPS54541 4.5-V to 42-V Input, 5-A Step-Down DC-DC Converter With Soft-Start and Eco-mode™

TPS54541
SLVSC57A – OCTOBER 2013 – REVISED AUGUST 2015
7 Detailed Description
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7.1 Overview
The TPS54541 is a 42-V 5-A, step-down (buck) regulator with an integrated high-side n-channel MOSFET. The
device implements constant-frequency current-mode control which reduces output capacitance and simplifies
external frequency compensation. The wide switching frequency range of 100 to 2500 kHz allows for either
efficiency or size optimization when selecting the output filter components. The switching frequency is adjusted
using a resistor to ground connected to the RT/CLK pin. The device has an internal phase-locked loop (PLL)
connected to the RT/CLK pin that synchronizes the power switch turn-on to a falling edge of an external clock
signal.
The TPS54541 device has a default input start-up voltage of 4.3 V typical. The EN pin adjusts the input-voltage
undervoltage-lockout (UVLO) threshold with two external resistors. An internal-pullup current source enables
operation when the EN pin is floating. The operating current is 152 μA under a no-load condition when not
switching. When the device is disabled, the supply current is 2 μA.
The integrated 87-mΩ high-side MOSFET supports high-efficiency power-supply designs capable of delivering 5
A of continuous current to a load. The gate-drive bias voltage for the integrated high-side MOSFET is supplied by
a bootstrap capacitor connected from the BOOT to SW pins. The TPS54541 device reduces the external
component count by integrating the bootstrap recharge diode. The BOOT pin capacitor voltage is monitored by a
UVLO circuit which turns off the high-side MOSFET when the BOOT to SW voltage falls below a preset
threshold. An automatic BOOT capacitor recharge circuit allows the TPS54541 device to operate at high duty
cycles approaching 100%. Therefore, the maximum output voltage is near the minimum input supply voltage of
the application. The minimum output voltage is the internal 0.8-V feedback reference.
Output overvoltage transients are minimized by an overvoltage protection (OVP) comparator. When the OVP
comparator is activated, the high-side MOSFET turns off and remains off until the output voltage is less than
106% of the desired output voltage.
The SS/TR (soft-start/tracking) pin minimizes inrush currents or provides power-supply sequencing during power
up. A small value capacitor must be connected to the pin to adjust the soft-start time. A resistor divider can be
connected to the pin for critical power supply sequencing requirements. The SS/TR pin is discharged before the
output powers up. This discharging ensures a repeatable restart after an overtemperature fault, UVLO fault, or a
disabled condition. When the overload condition is removed, the soft-start circuit controls the recovery from the
fault output level to the nominal regulation voltage. A frequency-foldback circuit reduces the switching frequency
during startup and overcurrent fault conditions to help maintain control of the inductor current.
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