SLVS839F July 2008 – October 2014 TPS54331
The TPS54331 device is a 28-V, 3-A, step-down (buck) converter with an integrated high-side n-channel MOSFET. To improve performance during line and load transients, the device implements a constant-frequency, current mode control which reduces output capacitance and simplifies external frequency compensation design. The TPS54331 device has a preset switching frequency of 570 kHz.
The TPS54331 device requires a minimum input voltage of 3.5 V for normal operation. The EN pin has an internal pullup current source that can adjust the input-voltage undervoltage lockout (UVLO) with two external resistors. In addition, the pullup current provides a default condition when the EN pin is floating for the device to operate. The operating current is 110 μA (typical) when not switching and under no load. When the device is disabled, the supply current is 1 μA (typical).
The integrated 80-mΩ high-side MOSFET allows for high-efficiency power-supply designs with continuous output currents up to 3 A.
The TPS54331 device reduces the external component count by integrating the boot recharge diode. The bias voltage for the integrated high-side MOSFET is supplied by an external capacitor on the BOOT to PH pin. The boot capacitor voltage is monitored by an UVLO circuit and turns the high-side MOSFET off when the voltage falls below a preset threshold of 2.1 V (typical). The output voltage can be stepped down to as low as the reference voltage.
By adding an external capacitor, the slow-start time of the TPS54331 device can be adjustable which enables flexible output filter selection.
To improve the efficiency at light load conditions, the TPS54331 device enters a special pulse skipping Eco-mode when the peak inductor current drops below 160 mA (typical).
The frequency foldback reduces the switching frequency during startup and overcurrent conditions to help control the inductor current. The thermal shutdown provides additional protection under fault conditions.