KB4863 datasheet(13/19 Pages) KINGBOR

13 / 19 page

Application Information (Continued)

mode or bridge mode, respectively. Twice the maximum

power dissipation point given by Equation (3) must not ex-

ceed the power dissipation given by Equation (4):

DMAX’= (TJMAX −TA)/

(4)

The KB4863’s T

JMAX = 150˚C. In the LQ (LLP) package

soldered to a DAP pad that expands to a copper area of 5in

on a PCB, the KB4863’s

JA is 20˚C/W. In the MTE package

soldered to a DAP pad that expands to a copper area of 2in

on a PCB , the KB4863’s

JA is 41˚C/W. At any given

ambient temperature T

J\A, use Equation (4) to find the maxi-

mum internal power dissipation supported by the IC packag-

ing. Rearranging Equation (4) and substituting PDMAX for

PDMAX’ results in Equation (5). This equation gives the

maximum ambient temperature that still allows maximum

stereo power dissipation without violating the KB4863’s

maximum junction temperature.

A =TJMAX −2xPDMAX

(5)

For a typical application with a 5V power supply and an 4

Ω

load, the maximum ambient temperature that allows maxi-

mum stereo power dissipation without exceeding the maxi-

mum junction temperature is approximately 99˚C for the LLP

package and 45˚C for the MTE package.

JMAX =PDMAX

JA +TA

(6)

Equation (6) gives the maximum junction temperature T

J-

MAX

. If the result violates the KB4863’s 150˚C, reduce the

maximum junction temperature by reducing the power sup-

ply voltage or increasing the load resistance. Further allow-

ance should be made for increased ambient temperatures.

The above examples assume that a device is a surface

mount part operating around the maximum power dissipation

point. Since internal power dissipation is a function of output

power, higher ambient temperatures are allowed as output

power or duty cycle decreases.

If the result of Equation (2) is greater than that of Equation

(3), then decrease the supply voltage, increase the load

impedance, or reduce the ambient temperature. If these

measures are insufficient, a heat sink can be added to

reduce

JA. The heat sink can be created using additional

copper area around the package, with connections to the

ground pin(s), supply pin and amplifier output pins. External,

solder attached SMT heatsinks such as the Thermalloy

7106D can also improve power dissipation. When adding a

heat sink, the

JA is the sum of

JC,

CS, and

SA.(

JC is the

junction−to−case thermal impedance,

CS is the case−to−sink

thermal impedance, and

SAis the sink−to−ambient thermal

impedance.) Refer to the Typical Performance Characteris-

tics curves for power dissipation information at lower output

power levels.

POWER SUPPLY BYPASSING

As with any power amplifier, proper supply bypassing is

critical for low noise performance and high power supply

rejection. Applications that employ a 5V regulator typically

use a 10µF in parallel with a 0.1µF filter capacitors to stabi-

lize the regulator’s output, reduce noise on the supply line,

and improve the supply’s transient response. However, their

presence does not eliminate the need for a local 1.0µF

tantalum bypass capacitance connected between the

KB4863’s supply pins and ground. Do not substitute a ce-

ramic capacitor for the tantalum. Doing so may cause oscil-

lation in the output signal. Keep the length of leads and

traces that connect capacitors between the KB4863’s power

supply pin and ground as short as possible. Connecting a

1µF capacitor, C

B, between the BYPASS pin and ground

improves the internal bias voltage’s stability and improves

the amplifier’s PSRR. The PSRR improvements increase as

the bypass pin capacitor value increases. Too large, how-

ever, increases turn-on time and can compromise amplifier’s

click and pop performance. The selection of bypass capaci-

tor values, especially C

B, depends on desired PSRR require-

ments, click and pop performance (as explained in the sec-

tion, Proper Selection of External Components), system

cost, and size constraints.

MICRO-POWER SHUTDOWN

The voltage applied to the SHUTDOWN pin controls the

KB4863’s shutdown function. Activate micro-power shut-

down by applying V

DD to the SHUTDOWN pin. When active,

the KB4863’s micro-power shutdown feature turns off the

amplifier’s bias circuitry, reducing the supply current. The

logic threshold is typically V

DD/2. The low 0.7µA typical

shutdown current is achieved by applying a voltage that is as

near as V

DD as possible to the SHUTDOWN pin. A voltage

thrat is less than V

DD may increase the shutdown current.

There are a few ways to control the micro-power shutdown.

These include using a single-pole, single-throw switch, a

microprocessor, or a microcontroller. When using a switch,

connect an external 10k

Ω pull-up resistor between the

SHUTDOWN pin and V

DD. Connect the switch between the

SHUTDOWN pin and ground. Select normal amplifier opera-

tion by closing the switch. Opening the switch connects the

SHUTDOWN pin to V

DD through the pull-up resistor, activat-

ing micro-power shutdown. The switch and resistor guaran-

tee that the SHUTDOWN pin will not float. This prevents

unwanted state changes. In a system with a microprocessor

or a microcontroller, use a digital output to apply the control

voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin

with active circuitry eliminates the pull up resistor.

TABLE 1. Logic level truth table for SHUTDOWN and

HP-IN Operation

SHUTDOWN

HP-IN PIN

OPERATIONAL MODE

Low

logic Low

Bridged amplifiers

Low

logic High

Single-Ended amplifiers

High

logic Low

Micro-power Shutdown

High

logic High

Micro-power Shutdown

HP-IN FUNCTION

Applying a voltage between 4V and V

DD to the KB4863’s

HP-IN headphone control pin turns off Amp2A and Amp2B,

muting a bridged-connected load. Quiescent current con-

sumption is reduced when the IC is in this single-ended

mode.

Figure 2 shows the implementation of the KB4863’s head-

phone control function. With no headphones connected to

the headphone jack, the R1-R2 voltage divider sets the

voltage applied to the HP-IN pin (pin 16) at approximately

50mV. This 50mV enables Amp1B and Amp2B, placing the

KB4863’s in bridged mode operation. The output coupling

capacitor blocks the amplifier’s half-supply DC voltage, pro-

tecting the headphones.

While the KB4863 operates in bridged mode, the DC poten-

tial across the load is essentially 0V. The HP-IN threshold is

set at 4V. Therefore, even in an ideal situation, the output

swing cannot cause a false single-ended trigger. Connecting

headphones to the headphone jack disconnects the head-

KingborTechnologyCo.,Ltd

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

KB4863

13/19

Rev: 1.1

2005-12-05

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