SLMA002 datasheet(25/55 Pages) TI1

25 / 55 page

www.ti.com

Inductor

Current

OUT

Ripple

SW Waveform

Steady State

= 12 V

OUT

= 5 V

SW Waveform

OUT

Ripple

Inductor

Current

Skipping

= 12 V

OUT

= 5 V

SW Node Ringing

TPS54283,, TPS54286

SLUS749C – JULY 2007 – REVISED OCTOBER 2007

Figure 31. Steady State

Figure 32. Skipping

DESIGN HINT

If additional output capacitance is required to reduce the output voltage ripple during

DCM operation, be sure to recheck Feedback Loop and Inductor-Capacitor (L-C)

Filter Selection and Maximum Output Capacitance sections.

A portion of the control circuitry is referenced to the SW node. To ensure jitter-free operation, it is necessary to

decrease the voltage waveform ringing at the SW node to less than 5 volts peak and of a duration of less than

30-ns. In addition to following good printed circuit board (PCB) layout practices, there are a couple of design

techniques for reducing ringing and noise.

SW Node Snubber

Voltage ringing observable at the SW node is caused by fast switching edges and parasitic inductance and

capacitance. If the ringing results in excessive voltage on the SW node, or erratic operation of the converter, an

R-C snubber may be used to dampen the ringing and ensure proper operation over the full load range.

DESIGN HINT

A series-connected R-C snubber (C = between 330 pF and 1 nF, R = 10

Ω)

connected from SW to GND reduces the ringing on the SW node.

Bootstrap Resistor

A small resistor in series with the bootstrap capacitor reduces the turn-on time of the internal MOSFET, thereby

reducing the rising edge ringing of the SW node.

DESIGN HINT

A resistor with a value between 1

Ω and 3Ω may be placed in series with the bootstrap

capacitor to reduce ringing on the SW node.

DESIGN HINT

Placeholders for these components should be placed on the initial prototype PCBs in

case they are needed.

Submit Documentation Feedback

Product Folder Link(s): TPS54283 TPS54286

SLMA002 Datasheet(PDF) 25 Page - Texas Instruments

SLMA002 Datasheet(HTML) 25 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Datasheet Download

Link URL