9.1 Overview

TPS65283, TPS65283-1 PMIC integrates dual synchronous step-down converter with regulated 0.6-V ±1% feedback reference voltage, 4.5- to 18-V Vin, 3.5-A/2.5-A output current, which is optimized for small designs through high efficiency and integrating the high-side and low-side MOSFETs. The device also incorporates one N-channel MOSFET power switches for power distribution systems. This device provides a total power distribution solution, where precision current limiting and fast protection response are required.

The TPS65283, TPS65283-1 implements a constant frequency, peak current mode control that simplifies external loop compensation. The wide switching frequency of 250 kHz to 2 MHz allows optimizing system efficiency and filtering size. The switching frequency can be adjusted with an external resistor connecting between ROSC pin and ground. The switch clock of buck1 is 180° out-of-phase operation from the clock of buck2 channel to reduce input current ripple, input capacitor size, and power supply induced noise.

The TPS65283, TPS65283-1 has been designed for safe monotonic start-up into pre-biased loads. The default start-up is when VIN is typically 4.5 V. The ENx pin has an internal pullup current source that can be used to adjust the input voltage UVLO with two external resistors. In addition, the ENx pin can be floating for automatically starting up the converters with the internal pullup current.

The TPS65283, TPS65283-1 reduces the external component count by integrating the bootstrap circuit. The bias voltage for the integrated high-side MOSFET is supplied by a capacitor between the BST and LX pins. A UVLO circuit monitors the bootstrap capacitor voltage VBST-VLX in each buck. When VBST-VLX voltage drops to the threshold, LX pin to be pulled low to recharge the boot capacitor. The TPS65283, TPS65283-1 can operate at 100% duty cycle as long as the boot capacitor voltage is higher than the preset BOOT-LX UVLO threshold, which is typically 2.1 V.

The TPS65283, TPS65283-1 features PGOOD pin to supervise output voltages of buck converter. The TPS65283, TPS65283-1 has power good comparators with hysteresis, which monitor the output voltages through internal feedback voltages. When the buck is in regulation range and power sequence is done, PGOOD is asserted to high.

The TPS65283, TPS65283-1 is protected from overload and thermal fault conditions. The converter minimizes excessive output overvoltage transients by taking advantage of the power good comparator. When the overvoltage comparator is activated, the high-side MOSFET is turned off and prevented from turning on until the internal feedback voltage is lower than 107.5% of the 0.6-V reference voltage. The TPS65283, TPS65283-1 implements both high-side MOSFET overload protection and bidirectional low-side MOSFET overload protections to avoid inductor current runaway. If the overcurrent condition has lasted for more than the hiccup wait time (4 ms), the converter shuts down and restarts after the hiccup time (64 ms). The TPS65283, TPS65283-1 shuts down if the junction temperature is higher than the thermal shutdown trip point. When the junction temperature drops 20°C typically below the thermal shutdown trip point, the TPS65283, TPS65283-1 is restarted under control of the soft-start circuit automatically. In light loading condition, TPS65283-1 automatically operates in PSM to save power.

Power distribution switches of TPS65283, TPS65283-1 use N-channel MOSFET for applications where short circuits or heavy capacitive loads will be encountered and provide a precision current limit protection. Additional device features include overtemperature protection and reverse-voltage protection. The device incorporates an internal charge pump and gate drive circuitry necessary to drive the N-channel MOSFET. The charge pump supplies power to the driver circuit and provide the necessary voltage to pull the gate of the MOSFET above the source. The charge pump operates from input voltage of power switches as low as 2.4 V and requires little supply current. The driver controls the gate voltage of power switch. The driver incorporates circuitry that controls the rise and fall times of output voltage to limit large current and voltage surges and provides built-in soft-start functionality. TPS65283, TPS65283-1 device limits output current to a safe level when output load exceeds the current limit threshold. The device asserts the nFAULT signal when overs current limit or reverse voltage faulty condition last longer than deglitching time. When the output voltage and current return normally, the device will auto recovery and nFAULT signal will be released.