´

>

´

OUT

OUT

IN

V

I

0.8

100 mA

V

´

ì

ï

´

í

ï

î

OUT

OUT

IN

L,MAX

V

I

+ 100 mA;

continous current operation

0.8 V

I

=

200 mA;

discontinuous current operation

´

´

´

IN

OUT

IN

OUT

V

(V

- V )

1

L =

f

200 mA

V

L

L

1

VIN

VOUT

FB

C

2

EN

GND

TPS61222

V

IN

C

1

TPS61222-EP

www.ti.com

SLVSBI2 – SEPTEMBER 2012

APPLICATION INFORMATION

DESIGN PROCEDURE

The TPS61222 DC/DC converter is intended for systems powered by a single cell battery to up to three Alkaline,

NiCd or NiMH cells with a typical terminal voltage between 0.7 V and 5.5 V. It can also be used in systems

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

any other voltage source with a typical output voltage between 0.7 V and 5.5 V can be used with the TPS61222.

Programming the Output Voltage

Output voltage

The output voltage is set by a resistor divider internally. The FB pin is used to sense the output voltage. To

configure the fixed output devices properly, the FB pin needs to be connected directly to VOUT as shown in

Figure 10.

Figure 10. Typical Application Circuit

Inductor Selection

To make sure that the TPS61222 can operate, a suitable inductor must be connected between pin VIN and pin L.

Inductor values of 4.7

μH show good performance over the whole input and output voltage range .

Choosing other inductance values affects the switching frequency f proportional to 1/L as shown in Equation 1.

(1)

Choosing inductor values higher than 4.7

μH can improve efficiency due to reduced switching frequency and

therefore with reduced switching losses. Using inductor values below 2.2

μH is not recommended.

Having selected an inductance value, the peak current for the inductor in steady state operation can be

calculated. Equation 2 gives the peak current estimate.

(2)

For selecting the inductor this would be the suitable value for the current rating. It also needs to be taken into

account that load transients and error conditions may cause higher inductor currents.

Equation 3 provides an easy way to estimate whether the device will work in continuous or discontinuous

operation depending on the operating points. As long as the inequation is true, continuous operation is typically

established. If the inequation becomes false, discontinous operation is typically established.

(3)

Copyright © 2012, Texas Instruments Incorporated

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