VIN = 8 - 17 V

VOUT = 3.3 V, 8 A

R7

10.0k

C7

47uF

C3

0.1uF

R6

0

R8

2.21k

R5

4.64k

C4

3900pF

C5

39pF

C1

10uF

R1

35.7k

R2

8.06k

R3

100k

1

RT/CLK

2

GND

3

GND

4

PVIN

5

PVIN

6

VIN

7

V_SNS

8

COMP

9

SS/TR

10

EN

11

PH

12

PH

13

BOOT

14

PWRGD

15

PWPD

U1

TPS54821RHL

C2

4.7uF

C6

0.022uf

C9

470pF

L1 3.3 uH

C8

47uF

R4

100k

EN

V_SNS

V_SNS

EN

PULL UP VOLTAGE

PWRGD

VIN

VOUT

TPS54821

SLVSB14

– OCTOBER 2011

www.ti.com

APPLICATION INFORMATION

Design Guide

– Step-By-Step Design Procedure

This example details the design of a high frequency switching regulator design using ceramic output capacitors.

A few parameters must be known in order to start the design process. These parameters are typically determined

at the system level. For this example, start with the following known parameters:

Table 1.

Parameter

Value

Output Voltage

3.3 V

Output Current

8 A

Transient Response 4 A load step

ΔVout = 7 %

Input Voltage

12 V nominal, 8 V to 17 V

Output Voltage Ripple

33 mV p-p

Start Input Voltage (Rising Vin)

6.528 V

Stop Input Voltage (Falling Vin)

6.193 V

Switching Frequency

480 kHz

Typical Application Schematic

The application schematic of Figure 29 was developed to meet the requirements above. This circuit is available

as the TPS54821EVM-049 evaluation module. The design procedure is given in this section. For more

information about Type II and Type III frequency compensation circuits, see Designing Type III Compensation for

Current Mode Step-Down Converters (SLVA352) and Design Calculator (SLVC219).

Figure 29. Typical Application Circuit

Operating Frequency

The first step is to decide on a switching frequency for the regulator. There is a trade off between higher and

20

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