TPS54341_15 datasheet(12/48 Pages) TI

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TPS54341

SLVSC61 – NOVEMBER 2013

www.ti.com

OVERVIEW

The TPS54341 device is a 42-V 3.5-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 TPS54341 device has a default input-startup 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-m

Ω high-side MOSFET supports high-efficiency power-supply designs capable of delivering

3.5 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 TPS54341 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 TPS54341 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.

DETAILED DESCRIPTION

Fixed Frequency PWM Control

The TPS54341 device uses fixed-frequency peak-current-mode control with adjustable switching frequency. The

output voltage is compared through external resistors connected to the FB pin to an internal voltage reference by

an error amplifier. An internal oscillator initiates the turn-on of the high-side power switch. The error amplifier

output at the COMP pin controls the high-side power switch current. When the high-side MOSFET switch current

reaches the threshold level set by the COMP voltage, the power switch turns off. The COMP pin voltage

increases and decreases as the output current increases and decreases. The device implements current limiting

by clamping the COMP pin voltage to a maximum level. The pulse skipping Eco-mode is implemented with a

minimum voltage clamp on the COMP pin.

Slope Compensation Output Current

The TPS54341 device adds a compensating ramp to the MOSFET switch current-sense signal. This slope

compensation prevents sub-harmonic oscillations at duty cycles greater than 50%. The peak current limit of the

high-side switch is not affected by the slope compensation and remains constant over the full duty-cycle range.

Pulse Skip Eco-mode

The TPS54341 device operates in a pulse-skipping Eco-mode at light load currents to improve efficiency by

reducing switching and gate drive losses. If the output voltage is within regulation and the peak switch current at

the end of any switching cycle is below the pulse skipping current threshold, the device enters Eco-mode. The

pulse-skipping current threshold is the peak switch-current level corresponding to a nominal COMP voltage of

600 mV.

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