TPS70950DBVT datasheet(13/39 Pages) TI

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Thermal

Shutdown

Current

Limit

Bandgap

OUT

Logic

GND

Device

TPS709

www.ti.com

SBVS186G – MARCH 2012 – REVISED NOVEMBER 2015

7 Detailed Description

7.1 Overview

The TPS709 series of devices are ultralow quiescent current, low-dropout (LDO) linear regulators. The TPS709

offers reverse current protection to block any discharge current from the output into the input. The TPS709 also

features current limit and thermal shutdown for reliable operation.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Internal Current Limit

The TPS709 internal current limit helps protect the regulator during fault conditions. During current limit, the

output sources a fixed amount of current that is largely independent of output voltage. In such a case, the output

voltage is not regulated, and can be measured as (VOUT = ILIMIT × RLOAD). The PMOS pass transistor dissipates

[(VIN – VOUT) × ILIMIT] until a thermal shutdown is triggered and the device turns off. When cool, the device is

turned on by the internal thermal shutdown circuit. If the fault condition continues, the device cycles between

current limit and thermal shutdown; see the Thermal Protection section for more details.

The TPS709 is characterized over the recommended operating output current range up to 150 mA. The internal

current limit begins to limit the output current at a minimum of 200 mA of output current. The TPS709 continues

to operate for output currents between 150 mA and 200 mA but some data sheet parameters may not be met.

7.3.2 Dropout Voltage

The TPS709 use a PMOS pass transistor to achieve low dropout voltage. When (VIN – VOUT) is less than the

dropout voltage (VDO), the PMOS pass device is in the linear region of operation and the input-to-output

resistance is the RDS(ON) of the PMOS pass element. VDO approximately scales with the output current because

the PMOS device functions like a resistor in dropout.

The ground pin current of many linear voltage regulators increases substantially when the device is operated in

dropout. This increase in ground pin current while operating in dropout can be several orders of magnitude larger

than when the device is not in dropout. The TPS709 employs a special control loop that limits the increase in

ground pin current while operating in dropout. This functionality allows for the most efficient operation while in

dropout conditions that can greatly increase battery run times.

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