R =

500 kHz

Switching Frequency

x 100 [k ]

TPS54972

SLVS437B – AUGUST 2002 – REVISED AUGUST 2010

www.ti.com

APPLICATION INFORMATION

Figure 8 shows the schematic diagram for a typical TPS54972 application. The TPS54972 (U1) can provide up to

PowerPAD underneath the integrated circuit TPS54972 is soldered directly to the printed-circuit board.

COMPONENT SELECTION

The values for the components used in this design example were selected for good transient response and small

PCB area. Ceramic dielectric 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 3.3 VDC. The input filter (C4) is a 10-µF ceramic capacitor (Taiyo Yuden).

Capacitor C8, a 10-mF ceramic capacitor (Taiyo Yuden) that provides high frequency decoupling of the

TPS54972 from the input supply, must be located as close as possible to the device. Ripple current is carried in

both C4 and C8, and the return path to PGND should avoid the current circulating in the output capacitors C7,

C9, C11, and C12.

FEEDBACK CIRCUIT

The values for these components are selected to provide fast transient response times. Components R1, R2, R3,

C1, C2, and C3 form 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 cross-over frequency is typically between 70

kHz and 80 kHz for input from 3 V to 4 V.

OPERATING FREQUENCY

In the application circuit, RT is grounded through a 71.5 k

Ω resistor to select the operating frequency of 700 kHz.

To set a different frequency, place a 68-k

Ω to 180-kΩ resistor between RT (pin 28) and analog ground or leave

RT floating to select the default of 350 kHz. The resistance can be approximated using the following equation:

(1)

8

Submit Documentation Feedback

Copyright © 2002–2010, Texas Instruments Incorporated