V =V

1+

O

−

R1=

−

V

REF

-1

)

VO

VI

OUT

FB

R2

GND

EN

IN

≤

0.9 V

TPS76901

1µF

3

1

4

2

R1

5

ESR = 0.2 Ω

4.7µF

TPS76901-HT

SLVS959C – JUNE 2009 – REVISED APRIL 2012

www.ti.com

Table 2. CAPACITOR SELECTION

PART NO.

MANUFACTURER

VALUE

T494B475K016AS

KEMET

4.7

μF

1.5

Ω

1.9 x 3.5 x 2.8

195D106x0016x2T

SPRAGUE

10

μF

1.5

Ω

1.3 x 7.0 x 2.7

695D106x003562T

SPRAGUE

10

μF

1.3

Ω

2.5 x 7.6 x 2.5

TPSC475K035R0600

AVX

4.7

μF

0.6

Ω

2.6 x 6.0 x 3.2

(1)

OUTPUT VOLTAGE PROGRAMMING

The output voltage of the TPS76901 adjustable regulator is programmed using an external resistor divider as

shown in Figure 7. The output voltage is calculated using:

(1)

Where:

Resistors R1 and R2 should be chosen for approximately 7-

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 = 169 k

Ω

to set the divider current at 7

μA and then calculate R1 using:

(2)

Note:

1.

The above calculations hold good for room temperature values only.

Figure 7. Adjustable LDO Reulator Programming

REGULATOR PROTECTION

The TPS76901 PMOS-pass transistor has a built-in back diode that 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 operation is anticipated, external limiting might be

appropriate.

The TPS76901 features internal current limiting protection. During normal operation, the TPS76901 limits output

current to approximately 350 mA. When current limiting engages, the output voltage scales back linearly until the

over current condition ends.

12

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