Datasheet


SLUS489 − OCTOBER 2001
22
www.ti.com
I
pk
+
ǒ
V
OUT
I
OUT
Ǔ
ǒ
h V
IN
Ǔ
)
ǒ
V
IN
D
Ǔ
ǒ
2 f
SW
L
Ǔ
where f
SW
is the switching frequency, L is the inductor value, and D is the duty cycle. The duty cycle for a flyback
converter is defined as:
D +
V
OUT
ǒ
V
IN
) V
OUT
Ǔ
Note that in these equations the voltage drop across the rectifier has been neglected.
SEPIC converter
The TPS43000 may also be used in the SEPIC topology. This topology, which is similar to the flyback, uses a
capacitor to aid in energy transfer from input to output. Figure 8 shows the TPS43000 in a SEPIC converter
(750 kHz) application with an input voltage range of 2.5 V to 6.0 V, an output voltage of 3.3 V, and a load current
from 0 A to 1 A.
UDG−01040
C9
10 µF
C8
120 µF
R5 1 kΩ
R6 1 kΩ
L1A
4.9 µH
C7
100 µF
R4
49.9 kΩ
R3
6.81 kΩ
R1
169 kΩ
C5
0.47 µF
C4
0.47 µF
C6
0.47 µF
R2
24.9 kΩ
C3
1200 pF
1
3
2
4
5
6
7
8
SYNC/SD
CCS
RT
CCM
BUCK
PFM
COMP
FB
TPS43000
9
10
11
12
13
14
15
16
VIN
VOUT
NDRV
GND
PDRV
VP
SWP
SWN
D1
ZHCS1000
(OPTIONAL)
Q1
Si9804DY
L1B
Q2
Si9803DY
D1 BAT54
R
BIAS
53.6 kΩ
C1
3900 pF
C2
82 pF
V
IN
V
OUT
Figure 8. 3.3-V Output SEPIC Topology
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