TPS6734I

FIXED 12-V 120-mA BOOST-CONVERTER SUPPLY

SLVS127A – AUGUST 1995 – REVISED JANUARY 1999

11

POST OFFICE BOX 655303

APPLICATION INFORMATION

efficiency

Typical efficiency for the converter circuit shown in Figure 13 is plotted in Figure 10. The efficiency falls off rapidly

at very light currents because the supply current is a significant percentage of the load.

82

80

76

74

10 20 30 40 50 60 70

84

86

EFFICIENCY

vs

OUTPUT CURRENT

88

80 90 100

140

78

110 120 130

IO – Output Current – mA

VCC = 5.5 V

VCC = 5 V

VCC = 4.5 V

Figure 10

inductor selection

Inductance value is directly proportional to the input voltage and inversely proportional to the output power. The

18

µH shown in the typical circuit is the proper value for operation from 5-V sources up to 2-W loads. A lower

inductance value should be used when operating from 3-V sources. Operation from 7 V and higher sources may

require inductance values greater than 18

µH. The inductor’s saturation current rating should be greater than

three times the dc load current for 5-V inputs and five times the dc load for 3-V inputs.

output filter capacitor selection

The output filter capacitor should be selected for minimum ESR (equivalent series resistance). Capacitor

ESR

voltage. The ESR of the capacitor should be less than 0.25

Ω to keep the output ripple less than 50 mV

peak-to-peak over the entire current range (using 18-

µH inductor).

diode

A Schottky diode or a high-speed silicon rectifier should be used. The continuous current rating of the diode

should be at least 300 mA for full load (120 mA) operation.