0

20

40

60

80

100

0.7

1.7

2.7

3.7

4.7

V - Input Voltage - V

I

I

= 50 mA

O

I

= 100

A

O

m

I

= 10 mA

O

I

= 1 mA

O

æ

ö

ç

÷

è

ø

OUT

FB

V

R

= R

x

- 1

1

2

V

TPS61220, TPS61221, TPS61222

SLVS776B – JANUARY 2009 – REVISED NOVEMBER 2014

www.ti.com

11.2.2.2.2

Programming The Output Voltage

In the adjustable output versions, an external resistor divider is used to adjust the output voltage. The resistor

divider must be connected between VOUT, FB and GND as shown in Figure 28. When the output voltage is

regulated properly, the typical voltage value at the FB pin is 500 mV for the adjustable devices. The maximum

recommended value for the output voltage is 6.0 V. The current through the resistor 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

calculated using Equation 5:

(5)

For this example, if an output voltage of 4.2 V is needed, a 1.2-M

11.2.2.2.3

Inductor Selection

See Inductor Selection for a discussion on inductor choice.

11.2.2.2.4

Capacitor Selection

The procedure for selecting capacitors is the same as for the fixed output voltage circuit. See Capacitor

Selection.

11.2.2.3 Application Curves

Figure 29 shows the excellent efficiency of the converter, which remains above 80% with heavily discharged

cells.

Figure 29. TPS61220 Performance

16

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