Datasheet

TPS61240, TPS61241

SLVS806B –APRIL 2009– REVISED FEBRUARY 2012

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ENABLE

The device is enabled setting EN pin to high. At first, the internal reference is activated and the internal analog

circuits are settled. Afterwards, the soft start is activated and the output voltage is ramped up. The output

voltages reaches its nominal value in typically 250 μs after the device has been enabled.

The EN input can be used to control power sequencing in a system with various DC/DC converters. The EN pin

can be connected to the output of another converter, to drive the EN pin high and getting a sequencing of supply

rails. With EN = GND, the device enters shutdown mode.

SOFT START

The TPS6124x has an internal soft start circuit that controls the ramp up of the output voltage. The output

voltages reaches its nominal value within t

Start

of typically 250μs after EN pin has been pulled to high level. The

output voltage ramps up from 5% to its nominal value within t

RAMP

of typ. 300μs.

This limits the inrush current in the converter during start up and prevents possible input voltage drops when a

battery or high impedance power source is used.

During soft start, the switch current limit is reduced to 300mA until the output voltage reaches V

. Once the

output voltage trips this threshold, the device operates with its nominal current limit I

LIMF

LOAD DISCONNECT

Load disconnect electrically removes the output from the input of the power supply when the supply is disabled.

This is especially important during shutdown. In shutdown of a boost converter, the load is still connected to the

input through the inductor and catch diode. Since the input voltage is still connected to the output, a small current

continues to flow, even when the supply is disabled. Even small leakage currents significantly reduce battery life

during extended periods of off time.

The benefit of this implemented feature for the system design engineer is that the battery is not depleted during

shutdown of the converter. No additional components must be added to the design to make sure that the battery

is disconnected from the output of the converter.

THERMAL SHUTDOWN

As soon as the junction temperature, T

, exceeds 140°C (typical) the device goes into thermal shutdown. In this

mode, the High Side and Low Side MOSFETs are turned-off. When the junction temperature falls below the

thermal shutdown hysteresis, the device continuous operation.