TPS7101Q, TPS7133Q, TPS7148Q, TPS7150Q

TPS7101Y, TPS7133Y, TPS7148Y, TPS7150Y

LOW-DROPOUT VOLTAGE REGULATORS

SLVS092G – NOVEMBER 1994 – REVISED JANUARY 2003

28

POST OFFICE BOX 655303

APPLICATION INFORMATION

programming the TPS7101 adjustable LDO regulator (continued)

Resistors R1 and R2 should be chosen for approximately 7-

µA divider current. A recommended value for R2

is 169 k

Ω with R1 adjusted for the desired output voltage. Smaller resistors can be used, but offer no inherent

advantage and consume more power. Larger values of R1 and R2 should be avoided as leakage currents at

FB introduce an error. Solving equation 1 for R1 yields a more useful equation for choosing the appropriate

resistance:

R1

+

V

O

V

ref

* 1 @ R2

OUTPUT

VOLTAGE

R1

R2

2.5 V

3.3 V

3.6 V

4 V

5 V

6.4 V

UNIT

191

309

348

402

549

750

169

169

169

169

169

169

k

Ω

k

Ω

k

Ω

k

Ω

k

Ω

k

Ω

OUTPUT VOLTAGE

PROGRAMMING GUIDE

VO

VI

PG

OUT

FB

R1

R2

GND

EN

IN

<0.5V

>2.7 V

TPS7101

Power-Good

Indicator

0.1

µF

250 k

Ω

+

Figure 44. TPS7101 Adjustable LDO Regulator Programming

power-good indicator

The TPS71xx features a power-good (PG) output that can be used to monitor the status of the regulator. The

internal comparator monitors the output voltage: when the output drops to between 92% and 98% of its nominal

regulated value, the PG output transistor turns on, taking the signal low. The open-drain output requires a pullup

resistor. If not used, it can be left floating. PG can be used to drive power-on reset circuitry or as a low-battery

indicator. PG does not assert itself when the regulated output voltage falls outside the specified 2% tolerance,

but instead reports an output voltage low, relative to its nominal regulated value.

regulator protection

The TPS71xx PMOS-pass transistor has a built-in back diode that safely conducts reverse currents 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. When extended reverse voltage is anticipated, external limiting may be

appropriate.

The TPS71xx also features internal current limiting and thermal protection. During normal operation, the

TPS71xx limits output current to approximately 1 A. 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 165

°C, thermal-protection circuitry shuts it down. Once the device has cooled, regulator

operation resumes.