Datasheet

TPS6734I
FIXED 12-V 120-mA BOOST-CONVERTER SUPPLY
SLVS127A – AUGUST 1995 – REVISED JANUARY 1999
13
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
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.
V
CC
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
V
I
2 V to 12 V
ENABLE
+
33 µF
V
O
12 V, 120 mA
0.0047 µF
Figure 11. TPS6734 Bootstrap Configuration
82
80
76
74
10 20 30 40 50 60 70
% – Efficiency
72
84
EFFICIENCY
vs
OUTPUT CURRENT FOR TYPICAL AND BOOTSTRAP
86
80 90 100 140
78
110120 130
I
O
– Output Current – mA
70
68
66
Typical
Bootstrap
V
CC
= 5 V
Figure 12