÷÷

ø

ö

çç

è

æ

-

×

=

1

V

V

2

R

1

R

FB

OUT

L

C

1

L

1

VIN

VOUT

FB

C

2

EN

GND

TPS61260

R

1

R

2

RI

R

3

OUT

I

V

200

3

R

=

(

)

s

2

.

0

I

V

V

V

V

L

OUT

2

OUT

IN

OUT

2

IN

MIN

×

×

×

-

×

=

TPS61260, TPS61261

SLVSA99

– MAY 2011

www.ti.com

APPLICATION INFORMATION

PROGRAMMING THE OUTPUT VOLTAGE

Within the TPS6126x family there are fixed and adjustable output voltage versions available. To properly

configure the fixed output voltage devices, the FB pin is used to sense the output voltage. This means that it

must be connected directly to VOUT. At the adjustable output voltage versions, an external resistor divider is

used to adjust the output voltage. The resistor divider must be connected between VOUT, FB and GND. When

the output voltage is regulated properly, the typical value of the voltage at the FB pin is 500 mV. The maximum

recommended value for the output voltage is 4.0 V. The current through the resistive divider should be about 100

times greater than the current into the FB pin. The typical current into the FB pin is 0.01

μA, and the voltage

value for R2 should be lower than 500 k

Ω, in order to set the divider current at 1 μA or higher. It is also

recommended to keep the total value for the resistor divider, R1 + R2, in the range of 1 M

Ω. From that, the value

calculated using Equation 1:

(1)

Figure 19. Typical Application Circuit for Adjustable Output Voltage Option

PROGRAMMING THE OUTPUT CURRENT

The devices of the TPS6126x family also support average output current regulation. An external resistor is used

to program the average output current. The resistor must be connected between RI and GND. When the average

output current is regulated properly, the typical value of the voltage at the RI pin is 400 mV. The maximum

recommended value for the regulated average output current is 100 mA. The value of the resistor R3 should be

between 2 k

Equation 2:

(2)

Accurate regulation of the average output current only is possible if the inductor current is continuous. Please

check the INDUCTOR SELECTION section to calculate the required parameters for selecting an appropriate

inductor.

INDUCTOR SELECTION

To properly configure the TPS6126x devices, an inductor must be connected between the supply voltage and pin

L. To estimate the minimum inductance value for accurate average output current regulation, Equation 3 can be

used.

(3)

12

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