=

´

OUT

ON

IN

SW

V

1

t

V

f

Time (ms)

Current

Feedback

t

ON

t

V

CS

V

COMP

UDG-10187

V

REF

TPS53317

SLUSAK4D – JUNE 2011 – REVISED JULY 2015

www.ti.com

7.3 Feature Description

7.3.1 PWM Operation

Referring to Figure 16, in steady state, continuous conduction mode, the converter operates in the following way.

comparator senses where the two waveforms cross and triggers the on-time generator.

Figure 16. D-CAP+™ Mode Basic Waveforms

The current feedback is an amplified and filtered version of the voltage between PGND and SW during low-side

accuracy and reduce the dependence of circuit performance on layout.

7.3.2 PWM Frequency and Adaptive On-Time Control

In general, the on-time (at the SW node) can be estimated by Equation 1.

where

•

(1)

The on-time pulse is sent to the top FET. The inductor current and the current feedback rises to peak value.

Each ON pulse is latched to prevent double pulsing. Switching frequency settings are shown in Table 1.

7.3.3 Light-Load Power Saving Features

The TPS53317 device has an automatic pulse-skipping mode to provide excellent efficiency over a wide load

range. The converter senses inductor current and prevents negative flow by shutting off the low-side gate driver.

This saves power by eliminating re-circulation of the inductor current. Further, when the bottom FET shuts off,

the converter enters discontinuous mode, and the switching frequency decreases, thus reducing switching losses

as well.

The device also provides a special light-load power saving feature, called ripple reduction. Essentially, it reduces

the on-time in SKIP mode to effectively reduce the output voltage ripple associated with using an all MLCC

capacitor output power stage design.

12

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