TPS6734I

FIXED 12-V 120-mA BOOST-CONVERTER SUPPLY

SLVS127A – AUGUST 1995 – REVISED JANUARY 1999

13

POST OFFICE BOX 655303

APPLICATION INFORMATION

bootstrapped output circuit

For operation below 2.7 V, the TPS6734 may be connected in a bootstrap configuration as shown in Figure 11.

The bootstrap configuration is less efficient (requires more supply current and suffers a loss in efficiency at

voltages below 5 V; see Figure 12) and is not recommended except for very low voltage operating conditions.

Because the output-driver stage, which benefits most from higher voltages, is diode-coupled to the output

voltage (see Figure 2), the bootstrapped configuration provides no benefit except at very low voltages. In the

shutdown mode (EN = low), no-load quiescent current is unchanged (3

µA max) whether in the bootstrap or the

typical configuration.

VCC

FB

OUT

GND

EN

REF

SS

COMP

1

2

3

4

8

7

6

5

TPS6734

0.001

µF

18

µH

1 A, 20 V

VI

2 V to 12 V

ENABLE

+

33

µF

VO

12 V, 120 mA

0.0047

µF

Figure 11. TPS6734 Bootstrap Configuration

82

80

76

74

10 20 30 40 50 60 70

72

84

EFFICIENCY

vs

OUTPUT CURRENT FOR TYPICAL AND BOOTSTRAP

86

80 90 100

140

78

110 120 130

IO – Output Current – mA

70

68

66

Typical

Bootstrap

VCC = 5 V

Figure 12