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R1 +

V

O

V

ref

* 1

R2

(4)

OUT

FB

R2

GND

EN

IN

TPS72101

OUTPUT

VOLTAGE

(V)

R1

R2

2.5

127

121

OUTPUT VOLTAGE

PROGRAMMING GUIDE

DIVIDER RESISTANCE

(k

Note (1): 1% values shown.

3

1

4

2

R1

5

0.1

µF

0.1

µF

REGULATOR PROTECTION

TPS72101

,, TPS72115

TPS72116, TPS72118

SLVS352C – DECEMBER 2001 – REVISED MARCH 2006

APPLICATION INFORMATION (continued)

Resistors R1 and R2 should be chosen for approximately 10-µA divider current. Lower value resistors can be

used but offer no inherent advantage and waste more power. Higher values should be avoided, as leakage

currents at FB increase the output voltage error. The recommended design procedure is to choose R2 = 30.1 k

Ω

to set the divider current at 10 µA and then calculate R1 using Equation 4:

Where:

• V

Figure 20. TPS72101 Adjustable LDO Regulator Programming

The TPS721xx pass element has a built-in back diode that safely conducts reverse current when the input

voltage drops below the output voltage (for example, during power down). Current is conducted from the output

to the input and is not internally limited. If extended reverse voltage is anticipated, external limiting might be

appropriate.

The TPS721xx also features internal current limiting and thermal protection. During normal operation, the

TPS721xx limits output current to approximately 350 mA. When current limiting engages, the output voltage

scales back linearly until the overcurrent condition ends. While current limiting is designed to prevent gross

device failure, care should be taken not to exceed the power dissipation ratings of the package. If the

temperature of the device exceeds 170°C, thermal-protection circuitry shuts it down. Once the device has cooled

down to below 150°C, regulator operation resumes.

9

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