TPS54873

SLVS444 – OCTOBER 2002

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 k

Ω

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 k

Ω

10 k

Ω

10 k

Ω

470 pF

12 pF

301

Ω

3.74 k

Ω

0.1

µF

22

µF

22

µF

22

µF

L1

0.65

µH

2.4 k

Ω

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.