7.1 Overview

The TPS54260 device is a 60-V, 2.5-A, step-down (buck) regulator 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 wide switching frequency of 100kHz to 2500kHz allows for efficiency and size optimization when selecting the output filter components. The switching frequency is adjusted using a resistor to ground on the RT/CLK pin. The device has an internal phase lock loop (PLL) on the RT/CLK pin that is used to synchronize the power switch turn on to a falling edge of an external system clock.

The TPS54260 has a default start up voltage of approximately 2.5V. The EN pin has an internal pull-up current source that can be used to adjust the input voltage under voltage lockout (UVLO) threshold with two external resistors. In addition, the pull up current provides a default condition. When the EN pin is floating the device will operate. The operating current is 138μA when not switching and under no load. When the device is disabled, the supply current is 1.3μA.

The integrated 200mΩ high side MOSFET allows for high efficiency power supply designs capable of delivering 2.5 amperes of continuous current to a load. The TPS54260 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 on the BOOT to PH pin. The boot capacitor voltage is monitored by an UVLO circuit and will turn the high side MOSFET off when the boot voltage falls below a preset threshold. The TPS54260 can operate at high duty cycles because of the boot UVLO. The output voltage can be stepped down to as low as the 0.8V reference.

The TPS54260 has a powergood comparator (PWRGD) which asserts when the regulated output voltage is less than 92% or greater than 109% of the nominal output voltage. The PWRGD pin is an open drain output which deasserts when the VSENSE pin voltage is between 94% and 107% of the nominal output voltage allowing the pin to transition high when a pull-up resistor is used.

The TPS54260 minimizes excessive output overvoltage (OV) transients by taking advantage of the OV powergood comparator. When the OV comparator is activated, the high-side MOSFET is turned off and masked from turning on until the output voltage is lower than 107%.

The SS/TR (slow-start / tracking) pin is used to minimize inrush currents or provide power supply sequencing during power-up. A small value capacitor should be coupled to the pin to adjust the slow-start time. A resistor divider can be coupled 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 over-temperature fault, UVLO fault or a disabled condition.

The TPS54260, also, discharges the slow-start capacitor during overload conditions with an overload recovery circuit. The overload recovery circuit will slow start the output from the fault voltage to the nominal regulation voltage once a fault condition is removed. A frequency foldback circuit reduces the switching frequency during start-up and overcurrent fault conditions to help control the inductor current.