KB4863 datasheet(15/19 Pages) KINGBOR

15 / 19 page

Application Information (Continued)

sents a tradeoff: as the size of C

B increases, the turn-on time

increases. There is a linear relationship between the size of

B and the turn-on time. Here are some typical turn-on times

for various values of C

0.01µF

20 ms

0.1µF

200 ms

0.22µF

440 ms

0.47µF

940 ms

1.0µF

2 Sec

In order eliminate ’clicks and pops’, all capacitors must be

discharged before turn-on. Rapidly switching V

DD may not

allow the capacitors to fully discharge, which may cause

’clicks and pops’. In a single-ended configuration, the output

is coupled to the load by C

OUT. This capacitor usually has a

high value. C

OUT discharges through internal 20k

Ω resistors.

Depending on the size of C

OUT, the discharge time constant

can be relatively large. To reduce transients in single-ended

mode, an external 1k

Ω -5kΩ resistor can be placed in

parallel with the internal 20k

Ω resistor. The tradeoff for using

this resistor is increased quiescent current.

NO LOAD STABILITY

The KB4863 may exhibit low level oscillation when the load

resistance is greater than 10k

Ω. This oscillation only occurs

as the output signal swings near the supply voltages. Pre-

vent this oscillation by connecting a 5k

Ω between the output

pins and ground.

AUDIO POWER AMPLIFIER DESIGN

Audio Amplifier Design: Driving 1W into an 8

Ω Load

The following are the desired operational parameters:

Power Output:

1Wrms

Load Impedance:

Ω

Input Level:

1Vrms

Input Impedance:

20k

Ω

Bandwidth:

100Hz−20 kHz ± 0.25 dB

The design begins by specifying the minimum supply voltage

necessary to obtain the specified output power. One way to

find the minimum supply voltage is to use the Output Power

vs Supply Voltage curve in the Typical Performance Char-

acteristics section. Another way, using Equation (4), is to

calculate the peak output voltage necessary to achieve the

desired output power for a given load impedance. To ac-

count for the amplifier’s dropout voltage, two additional volt-

ages, based on the Dropout Voltage vs Supply Voltage in the

Typical Performance Characteristics curves, must be

added to the result obtained by Equation (8). The result in

Equation (9).

(8)

≥ (V

OUTPEAK +(VODTOP +VODBOT))

(9)

The Output Power vs Supply Voltage graph for an 8

Ω load

indicates a minimum supply voltage of 4.6V. This is easily

met by the commonly used 5V supply voltage. The additional

voltage creates the benefit of headroom, allowing the

KB4863 to produce peak output power in excess of 1W

without clipping or other audible distortion. The choice of

supply voltage must also not create a situation that violates

maximum power dissipation as explained above in the

Power Dissipation section.

After satisfying the KB4863’s power dissipation require-

ments, the minimum differential gain is found using Equation

(10).

(10)

Thus, a minimum gain of 2.83 allows the KB4863’s to reach

full output swing and maintain low noise and THD+N perfor-

mance. For this example, let A

VD =3.

The amplifier’s overall gain is set using the input (R

i) and

feedback (R

f) resistors. With the desired input impedance

set at 20k

Ω, the feedback resistor is found using Equation

(11).

f/Ri =AVD/2

(11)

The value of R

f is 30k

Ω.

The last step in this design example is setting the amplifier’s

−3dB frequency bandwidth. To achieve the desired ±0.25dB

pass band magnitude variation limit, the low frequency re-

sponse must extend to at least one−fifth the lower bandwidth

limit and the high frequency response must extend to at least

five times the upper bandwidth limit. The gain variation for

both response limits is 0.17dB, well within the ±0.25dB

desired limit. The results are an

L = 100Hz/5 = 20Hz

(12)

and an

H = 20kHzx5 = 100kHz

(13)

As mentioned in the External Components section, R

and C

i create a highpass filter that sets the amplifier’s lower

bandpass frequency limit. Find the coupling capacitor’s

value using Equation (12).

the result is

1/(2

π*20kΩ*20Hz) = 0.398µF

(14)

Use a 0.39µF capacitor, the closest standard value.

The product of the desired high frequency cutoff (100kHz in

this example) and the differential gain, A

VD, determines the

upper passband response limit. With A

VD = 3 and fH =

100kHz, the closed-loop gain bandwidth product (GBWP) is

300kHz. This is less than the KB4863’s 3.5MHz GBWP. With

this margin, the amplifier can be used in designs that require

more differential gain while avoiding performance-lrestricting

bandwidth limitations.

RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT

Figures 3 through 6 show the recommended two-layer PC

board layout that is optimized for the 20-pin MTE-packaged

KB4863 and associated external components. Figures 7

through 11 show the recommended four-layer PC board

layout that is optimized for the 24-pin LQ-packaged KB4863

and associated external components. These circuits are de-

signed for use with an external 5V supply and 4

Ω speakers.

These circuit boards are easy to use. Apply 5V and ground to

the board’s V

DD and GND pads, respectively. Connect 4

Ω

speakers between the board’s -OUTA and +OUTA and

OUTB and +OUTB pads.

KingborTechnologyCo.,Ltd

TEL:(86)0755-83095458 FAX:(86)0755-88364052

KB4863

15/19

Rev: 1.1

2005-12-05

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