TPS65257RHAR

TPS65257 is a power management IC featuring three step-down buck converters. Integrated high-side and low-side MOSFETs enable fully synchronous conversion for higher efficiency. The converters are designed to simplify application while allowing designers to optimize their implementation for the target application. The converters operate in 5V, 9V, 12V, or 15V systems. The output voltage can be externally set via a resistor divider to any value between 0.8V and the input voltage minus the resistive voltage drop across the converter path. Each converter features a dedicated enable pin allowing delayed startup for sequencing purposes, a soft-start pin for adjustable soft-start timing via selection of the soft-start capacitor, and a current limit (RLIM) pin enabling designers to adjust the current limit and optimize inductor selection by choosing an external resistor. All converters operate in hiccup mode: once an overcurrent condition lasting more than 10ms is detected in any converter, they are shut down for 10ms, then retry the startup sequence. If the overload has been removed, the converter ramps up and resumes normal operation. Otherwise, the converter detects another overcurrent event, shuts down again, and repeats this cycle (hiccup) until the fault is cleared. If the overload condition lasts less than 10ms, only the affected converter is shut down and restarted without triggering the global hiccup mode. The switching frequency of these converters is set by an external resistor connected to the ROSC pin. The switching regulators are designed to operate in the frequency range of 300kHz to 2.2MHz. The converters operate with a 180° phase offset to significantly reduce input filtering requirements. All converters feature peak current mode control, which simplifies external frequency compensation. The device incorporates a built-in slope compensation ramp. Slope compensation prevents subharmonic oscillation in peak current mode control. A conventional Type II compensation network stabilizes the system and achieves fast transient response. Additionally, an optional capacitor placed in parallel with the upper resistor of the feedback divider adds an extra zero, enabling the crossover frequency to exceed 100kHz. All converters feature automatic light-load PFM skip mode, which improves efficiency during light-load and standby operation while maintaining extremely low output ripple, achieving less than 2% at low output voltages. The device incorporates an overvoltage transient protection circuit to minimize voltage overshoot. The OVP feature minimizes output overshoot by implementing a circuit that compares the FB pin voltage against the OVP threshold (109% of the internal voltage reference). If the FB pin voltage exceeds the OVP threshold, the high-side MOSFET is disabled to prevent current from flowing into the output, significantly reducing output overshoot. When the FB voltage drops below the lower OVP threshold (107% of the internal voltage reference), the high-side MOSFET is allowed to turn on at the next clock cycle. The TPS65257 features a monitoring circuit that monitors the output of each buck converter, with the PGOOD pin asserted upon completion of sequencing. The PGOOD pin is an open-drain output. It is pulled low when any buck converter output drops below 85% of its nominal output voltage. PGOOD is pulled high when all converter outputs exceed 90% of their respective nominal output voltages. The default reset time is 100ms. PGOOD polarity is active high. The pushbutton operation is designed to enable automatic system startup upon application of input power, or to provide integrated on/off system management without additional external components. The device operation depends on the state of the INT pin (see Startup Signals). The USB switch provides up to 1A of current required by downstream USB devices. When the output load exceeds the current limit threshold or a short circuit occurs, the PMU limits the output current to a safe level by switching to constant current mode and pulling the overcurrent logic output low. When sustained heavy loading and short circuits increase power dissipation in the switch, causing the junction temperature to rise, an overtemperature protection circuit shuts down the USB switch while allowing the buck converters to continue operating. The device implements an internal thermal shutdown to protect itself from damage when the junction temperature exceeds 160°C. When the junction temperature exceeds the thermal shutdown threshold, the device is forced to stop operating. Once the die temperature drops below 140°C, the device restarts the power-on sequence. The thermal shutdown hysteresis is 20°C.

Key features

• Wide input supply voltage range: 4.5V - 16V
• 0.8V, ±1% accuracy reference
• Continuous load: 3A (Buck 1), 2A (Buck 2 and Buck 3)
• Peak current: 3.5A (Buck 1), 2.5A (Buck 2 and Buck 3)
• Synchronous operation, switching frequency 300kHz - 2.2MHz set by external resistor
• External enable pin with built-in current source for easy sequencing
• External soft-start pin
• Adjustable cycle-by-cycle current limit set by external resistor
• Current mode control with simple compensation network
• Automatic low pulse skip mode (PSM) for output ripple better than 2%
• Pre-biased output support
• Power good monitor and reset generator
• 1A USB power switch with overcurrent and thermal protection
• Push-button (10kV ESD rated for PB_IN) control for intelligent system power-on/power-off operation
• Compact, thermally efficient 40-pin 6mm x 6mm RHA (QFN) package
• Junction temperature range: -40°C to 125°C