TPS709_17 Datasheet, PDF (13/34 Pages) Texas Instruments – 150-mA, 30-V, 1-uA IQ Voltage Regulators with Enable

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7 Detailed Description
TPS709
SBVS186G – MARCH 2012 – REVISED NOVEMBER 2015
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
IN
Current
Limit
Thermal
Shutdown
OUT
EN
Bandgap
Logic
Device
GND
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 (V_OUT = I_LIMIT × R_LOAD). The PMOS pass transistor dissipates
[(V_IN – V_OUT) × I_LIMIT] 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 (V_IN – V_OUT) is less than the
dropout voltage (V_DO), the PMOS pass device is in the linear region of operation and the input-to-output
resistance is the R_DS(ON) of the PMOS pass element. V_DO 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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