www.ti.com

APPLICATION INFORMATION

DESIGN PROCEDURE

Programming the Output Voltage

OUT

FB

V

R1 = R2 x

- 1

V

æ

ö

ç

÷

è

ø

(1)

L

VIN

EN

UVLO

PS

GND

PGND

FB

VAUX

VOUT

TPS61200

VIN

VOUT

C1

C2

C3

L1

R1

R2

R3

R4

Programming the UVLO Threshold Voltage

TPS61200

TPS61201

TPS61202

SLVS577B – MARCH 2007 – REVISED FEBRUARY 2008

The TPS6120x DC/DC converters are intended for systems powered by a single up to triple cell Alkaline, NiCd,

NiMH battery with a typical terminal voltage between 0.7 V and 5.5 V. They can also be used in systems

powered by one-cell Li-Ion or Li-Polymer with a typical voltage between 2.5 V and 4.2 V. Additionally, any other

voltage source like solar cells or fuel cells with a typical output voltage between 0.3 V and 5.5 V can power

systems where the TPS6120x is used.

Within the TPS6120X 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 5.5 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

to keep the value for this resistor in the range of 200 k

Ω. The value of the resistor connected between VOUT and

If as an example, an output voltage of 3.3 V is needed, a 1-M

180-k

Ω has been selected.

Figure 24. Typical Application Circuit for Adjustable Output Voltage Option

The UVLO input can be used to shut down the main output if the supply voltage is getting too low. The internal

reference threshold is typically 250 mV. If the supply voltage should cause the shutdown when it is dropping

below 250 mV, it can be connected directly to the UVLO pin. If the shutdown has already happen at higher

voltages, a resistor divider can be used. R3 and R4 in Figure 24 show an example of how to monitor the input

voltage of the circuit. The current through the resistive divider should be about 100 times greater than the current

into the UVLO pin. The typical current into the UVLO pin is 0.01

µA, and the voltage across R4 is equal to the

UVLO voltage threshold that is generated on-chip, which has a value of 250 mV. The recommended value for R4

is; therefore, in the range of 250 k

Ω. From this, the value of resistor R3, depending on the desired shutdown

Copyright © 2007–2008, Texas Instruments Incorporated

Submit Documentation Feedback

15

Product Folder Link(s): TPS61200 TPS61201 TPS61202