8.1 Overview

The TPS57112C-Q1 device is a 6-V, 2-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 wide switching-frequency range of 200 kHz to 2000 kHz allows for efficiency and size optimization when selecting the output-filter components. The switching-frequency adjustment uses a resistor to ground on the RT/CLK pin. The device has an internal phase-lock loop (PLL) on the RT/CLK pin that synchronizes the power-switch turnon to the falling edge of an external system clock.

The TPS57112C-Q1 device has a typical default start-up voltage of 2.45 V. The EN pin has an internal pullup current source that one can use to adjust the undervoltage lockout (UVLO) of the input voltage with two external resistors. In addition, the pullup current provides a default condition that allows the device to operate when the EN pin is floating. The total operating current for the TPS57112C-Q1 device is typically 515 μA when not switching and under no load. When the device is disabled, the supply current is typically 5.5 μA.

The integrated 12-mΩ MOSFETs allow for high-efficiency power-supply designs with continuous output currents up to 2 A.

The TPS57112C-Q1 device reduces the external component count by integrating the boot recharge diode. The bias-voltage supply for the integrated high-side MOSFET is from a capacitor between the BOOT and PH pins. A UVLO circuit monitors the boot-capacitor voltage and turns off the high-side MOSFET when the voltage falls below a preset threshold. This BOOT circuit allows the TPS57112C-Q1 device to operate approaching 100% duty cycle. The lower limit for stepping down the output voltage is the 0.8-V reference.

The TPS57112C-Q1 device has a power-good comparator (PWRGD) with 2% hysteresis.

The TPS57112C-Q1 device minimizes excessive output overvoltage transients by taking advantage of the overvoltage power-good comparator. The regulated output voltage exceeding 109% of the nominal voltage activates the overvoltage comparator, turning off the high-side MOSFET and masking it from turning on until the output voltage is lower than 107% of the nominal voltage.

A use of the SS/TR (slow-start or tracking) pin is to minimize inrush currents or provide power-supply sequencing during power up. Couple a small-value capacitor to the pin for slow start. The SS/TR pin discharges before the output power up to ensure a repeatable restart after an overtemperature fault, UVLO fault, or disabled condition.

The use of a frequency foldback circuit reduces the switching frequency during start-up and overcurrent fault conditions to help limit the inductor current.