TPS61253, TPS61254, TPS61256, TPS61258, TPS61259

SLVSAG8E – SEPTEMBER 2011 – REVISED MARCH 2015

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Feature Description (continued)

9.3.3 Load Disconnect and Reverse Current Protection

Regular boost converters do not disconnect the load from the input supply and therefore a connected battery will

be discharged during shutdown. The advantage of TPS6125x is that this converter disconnects the output from

the input of the power supply when it is disabled (so called true shutdown mode). In case of a connected battery

it prevents it from being discharged during shutdown of the converter.

9.3.4 Softstart

The TPS6125x device has an internal softstart circuit that limits the inrush current during start-up. The first step

in the start-up cycle is the pre-charge phase. During pre-charge, the rectifying switch is turned on until the output

capacitor is charged to a value close to the input voltage. The rectifying switch is current limited (approximately

200 mA) during this phase. This mechanism is used to limit the output current under short-circuit condition.

Once the output capacitor has been biased to the input voltage, the converter starts switching. The soft-start

system progressively increases the on-time as a function of the input-to-output voltage ratio. As soon as the

output voltage is reached, the regulation loop takes control and full current operation is permitted.

9.3.5 Undervoltage Lockout

The under voltage lockout circuit prevents the device from malfunctioning at low input voltages and the battery

threshold plus its hysteresis of 100 mV at typically 2.1 V.

9.3.6 Thermal Regulation

The TPS6125x device contains a thermal regulation loop that monitors the die temperature during the pre-charge

phase. If the die temperature rises to high values of about 110 °C, the device automatically reduces the current

to prevent the die temperature from increasing further. Once the die temperature drops about 10 °C below the

threshold, the device will automatically increase the current to the target value. This function also reduces the

current during a short-circuit condition.

9.3.7 Thermal Shutdown

mode, the high-side and low-side MOSFETs are turned-off. When the junction temperature falls below the

thermal shutdown minus its hysteresis, the device continuous the operation.

9.4 Device Functional Modes

9.4.1 Power Save Mode

The TPS6125x integrates a power save mode to improve efficiency at light load. In power save mode the

converter only operates when the output voltage trips below a set threshold voltage.

It ramps up the output voltage with several pulses and goes into power save mode once the output voltage

exceeds the set threshold voltage.

The PFM mode is left and PWM mode entered in case the output current can not longer be supported in PFM

mode.

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