RT5508WSC datasheet(25/57 Pages) RICHTEK

25 / 57 page

RT5508

is a registered trademark of Richtek Technology Corporation

DS5508-01

March

2017

www.richtek.com

Clip control is used to reduce current consumption

when VBAT is low. It is defined by three parameters,

VBCPS, CPSLP and MINCLS. The clip threshold is

shown in Figure.

The voltage sent to class-D is clipped when VBAT is

lower than clip point (2.85V to 3.9V) which is set by

VBCPS.

The slope of clip threshold (Vo/VBAT) can

be set by CPSLP from 2.5V/V to 3.4375V/V. A VO stop

point (0, 2.5V, 3V, 3.5V) for clip threshold can be set

via MINCLS. The output voltage drop will stops at this

point. The clip threshold is calculated through following

equation :

BAT

ClipThres = 5-(VBCPS-V

) CPSLP



for

clip

threshold ≧ MINCLS

ClipThres = MINCLS for clip threshold ≦ MINCLS

After clip is done, a threshold is passed to speaker

protection. Combined with speaker protection algorithm,

a gain reduced procedure will be activated by speaker

protection block and output signal is reduced to prevent

clip. The detail function is shown below, the dropping

rate of threshold can be set via CLIPDR at register

0x0B :

CLIPDR

old threshold

new threshold

CLIP

Speaker protection

gain reduced

Figure 20. Clipper Gain Step Down

The threshold is normalized to 1 is passed to speaker

protection which equals to :

BAT

5 - (VBCPS - V

) CPSLP

ClipThres (normalized) =



ClipThres (normalized) equals to 1 if signal is small and

never reaches to the threshold. When signal is large

and is clipped by this threshold, ClipThres (normalized)

will be sent to speaker protection block.

If battery voltage returns to a hysteresis level,

ClipThres will increase by a rate of CLIPRR to a certain

level which is defined by VBCPS, CPSLP and VBAT.

As ClipThres increases, speaker protection will also

increase its gain to let the signal return to its original

level.

The battery voltage hysteresis can bet set via

BVHYS at register 0x0B.

VBAT (Thr) + BVHYS

VBAT (Thr)

CLIPRR

ClipThres

Figure 21. Clipper Gain Step Up

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