Datasheet

TPS54873
SLVS444A − OCTOBER 2002 − REVISED FEBRUARY 2005
www.ti.com
8
APPLICATION INFORMATION
Figure 9 shows the schematic diagram for a typical
TPS54873 application. The TPS54873 (U1) can provide
up to 8 A of output current at a nominal output voltage of
0.9 V to 3.3 V, and for this application, the output voltage
is set at 3.3 V. For proper operation, the PowerPAD
underneath the integrated circuit TPS54873 must be
soldered properly to the printed-circuit board.
R6
71.5 kΩ
28
27
26
25
0.047 µF
4
3
2
1
24
23
22
21
20
14
13
12
11
10
9
8
7
6
5
19
18
17
16
15
1 µF
10 kΩ
10 kΩ 10 kΩ
470 pF
12 pF
301 Ω
3.74 kΩ
0.1 µF 22 µF 22 µF 22 µF
L1
0.65 µH
2.4 kΩ
3300 pF
0.047 µF
10 µF
470 pF
10 µF
VIN
1 A, 200 V
D1
1 A, 200 V
D2
RT
SYNCH
SS/ENA
VBIAS
PWRGD
COMP/NC
VSENSE
ANGND
PowerPAD
VIN
VIN
VIN
VIN
VIN
PH
PH
PH
PH
PH
PH
PH
PH
PH
BOOT
PGND
PGND
PGND
PGND
PGND
U1
TPS54873
C6
C3
R5
R1
R3
C4
C1
R2
C2
R4
VOUT
C13 C5 C7 C8
R7
C11
C9
C10 C12
VIN
1 A, 200 V
D3
1 A, 200 V
D4
Figure 9. Application Circuit
COMPONENT SELECTION
The values for the components used in this design
example are selected for low output ripple and small PCB
area. Ceramic capacitors are utilized in the output filter
circuit. A small size, small value output inductor is also
used. Compensation network components are chosen to
maximize closed loop bandwidth and provide good
transient response characteristics. Additional design
information is available at www.ti.com.
INPUT VOLTAGE
The input voltage is a nominal 5. VDC. The input filter
(C12) is a 10-µF ceramic capacitor (Taiyo Yuden). C10,
also a 10-µF ceramic capacitor (Taiyo Yuden) that
provides high frequency decoupling of the TPS54873 from
the input supply, must be located as close as possible to
the device. Ripple current is carried in both C10 and C12,
and the return path to PGND should avoid the current
circulating in the output capacitors C5, C7, C8, and C13.
FEEDBACK CIRCUIT
The values for these components are selected to provide
fast transient response times. R1, R2, R3, R4, C1, C2, and
C4 forms the loop-compensation network for the circuit.
For this design, a Type 3 topology is used. The transfer
function of the feedback network is chosen to provide
maximum closed loop gain available with open loop
characteristics of the internal error amplifier. Closed loop
crossover frequency is typically between 80 kHz and
135 kHz for input from 3 V to 6 V.