TPS54331 TPS54332 3.5V to 28V Input, 3A, 570kHz Step-Down Converter with Eco-mode

The TPS54331 is a 28-V, 3-A non-synchronous buck converter that integrates a low R_DS(on) high side MOSFET. To increase efficiency at light loads, a pulse skipping Eco-mode™ feature is automatically activated. Furthermore, the 1 µA shutdown supply current allows the device to be used in battery powered applications. Current mode control with internal slope compensation simplifies the external compensation calculations and reduces component count while allowing the use of ceramic output capacitors. A resistor divider programs the hysteresis of the input under-voltage lockout. An overvoltage transient protection circuit limits voltage overshoots during startup and transient conditions. A cycle by cycle current limit scheme, frequency fold back and thermal shutdown protect the device and the load in the event of an overload condition. The TPS54331 is available in 8-pin SOIC package and 8-pin SOIC PowerPAD^TM package that have been internally optimized to improve thermal performance.

The TPS54332 is a 28 V, 3.5 A non-synchronous buck converter that integrates a low R_DS(on) high side MOSFET. To increase efficiency at light loads, a pulse skipping Eco-mode™ feature is automatically activated. Furthermore, the 1 µA shutdown supply current allows the device to be used in battery powered applications. Current mode control with internal slope compensation simplifies the external compensation calculations and reduces component count while allowing the use of ceramic output capacitors. A resistor divider programs the hysteresis of the input under-voltage lockout. An overvoltage transient protection circuit limits voltage overshoots during startup and transient conditions. A cycle by cycle current limit scheme, frequency fold back and thermal shutdown protect the device and the load in the event of an overload condition. The TPS54332 is available in an 8-pin SOIC PowerPAD package.

ENABLE AND ADJUSTABLE INPUT UNDER-VOLTAGE LOCKOUT (VIN UVLO)

The EN pin has an internal pull-up current source that provides the default condition of the TPS54331 operating
when the EN pin floats.
The TPS54331 is disabled when the VIN pin voltage falls below internal VIN UVLO threshold. It is recommended
to use an external VIN UVLO to add Hysteresis unless VIN is greater than (VOUT + 2 V). To adjust the VIN UVLO
with Hysteresis, use the external circuitry connected to the EN pin as shown in Figure 14. Once the EN pin
voltage exceeds 1.25 V, an additional 3 μA of hysteresis is added. Use Equation 1 and Equation 2 to calculate
the resistor values needed for the desired VIN UVLO threshold voltages. The VSTART is the input start threshold
voltage, the VSTOP is the input stop threshold voltage and the VEN is the enable threshold voltage of 1.25 V. The
VSTOP should always be greater than 3.5 V.

PROGRAMMABLE SLOW START USING SS PIN

It is highly recommended to program the slow start time externally because no slow start time is implemented
internally. The TPS54331 effectively uses the lower voltage of the internal voltage reference or the SS pin
voltage as the power supply’s reference voltage fed into the error amplifier and will regulate the output
accordingly. A capacitor (CSS) on the SS pin to ground implements a slow start time. The TPS54331 has an
internal pull-up current source of 2μA that charges the external slow start capacitor. The equation for the slow
start time (10% to 90%) is shown in Equation 3 . The Vref is 0.8 V and the ISS current is 2 μA.

The slow start time should be set between 1ms to 10 ms to ensure good start-up behavior. The slow start
capacitor should be no more than 27nF.
If during normal operation, the input voltage drops below the VIN UVLO threshold, or the EN pin is pulled below
1.25 V, or a thermal shutdown event occurs, the TPS54331 stops switching.

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