TPS72101, TPS72115

TPS72116, TPS72118

SLVS352B – DECEMBER 2001 – REVISED MAY 2002

www.ti.com

9

PROGRAMMING THE TPS72101 ADJUSTABLE LDO REGULATOR

The output voltage of the TPS72101 adjustable regulator is programmed using an external resistor divider as shown in

Figure 18. The output voltage is calculated using:

V

O +

V

ref

1

) R1

R2

(1)

Where:

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 = 121 k

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

R1

+

V

O

V

ref

* 1

R2

(2)

Where:

VO

VI

OUT

FB

R2

GND

EN

IN

TPS72101

OUTPUT

VOLTAGE

(V)

R1

R2

2.5

3.3

127

205

121

121

OUTPUT VOLTAGE

PROGRAMMING GUIDE

DIVIDER RESISTANCE

(k

Ω)†

† 1% values shown.

3

1

4

2

R1

5

0.1

µF

0.1

µF

Figure 18. TPS72101 Adjustable LDO Regulator Programming

REGULATOR PROTECTION

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

below the output voltage (e.g., 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.