TPS54335A_15 Datasheet, PDF (9/46 Pages) Texas Instruments – TPS5433xA 4.5- to 28-V Input, 3-A Output, Synchronous SWIFT™ Step-Down DC-DC Converter

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8 Detailed Description
TPS54335A, TPS54335-1A, TPS54336A
SLVSCD5C – NOVEMBER 2014 – REVISED JULY 2015
8.1 Overview
The device is a 28-V, 3-A, synchronous step-down (buck) converter with two integrated n-channel MOSFETs. To
improve performance during line and load transients the device implements a constant-frequency, peak current-
mode control which reduces output capacitance and simplifies external frequency-compensation design.
The device has been designed for safe monotonic startup into pre-biased loads. The device has a typical default
startup voltage of 4 V. The EN pin has an internal pullup-current source that can provide a default condition when
the EN pin is floating for the device to operate. The total operating current for the device is 310 µA (typical) when
not switching and under no load. When the device is disabled, the supply current is less than 5 μA.
The integrated 128-mΩ and 84-mΩ MOSFETs allow for high-efficiency power-supply designs with continuous
output currents up to 3 A.
The device reduces the external component count by integrating the boot recharge diode. The bias voltage for
the integrated high-side MOSFET is supplied by a capacitor between the BOOT and PH pins. The boot capacitor
voltage is monitored by an UVLO circuit and turns off the high-side MOSFET when the voltage falls below a
preset threshold. The output voltage can be stepped down to as low as the 0.8-V reference voltage.
The device minimizes excessive output overvoltage transients by taking advantage of the overvoltage power-
good comparator. When the regulated output voltage is greater than 106% of the nominal voltage, the
overvoltage comparator is activated, and the high-side MOSFET is turned off and masked from turning on until
the output voltage is lower than 104%.
The TPS54335A device has a wide switching frequency of 50 kHz to 1500 kHz which allows for efficiency and
size optimization when selecting the output filter components. The internal 2-ms soft-start time is implemented to
minimize inrush currents.
The TPS54336A device has a fixed 340-kHz switching frequency. The device adjusts the soft-start time with the
SS pin.
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Product Folder Links: TPS54335A TPS54335-1A TPS54336A