HM4863 datasheet(13/21 Pages) HMSEMI

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Dual 2.2W Audio Amplifier Plus Stereo Headphone Function

Application Information

Exposed-DAP Mounting Considerations

The exposed-DAP must be connected to ground.

The exposed-DAP package of the HM4863 re-

quires special attention to thermal design. If

thermal design issues are not properly addressed,

an HM4863 driving 4Ω will go into thermal shut-

down.

The exposed-DAP on the bottom of the HM4863

should be soldered down to a copper pad on the

circuit board. Heat is conducted away from the

exposed-DAP by a copper plane. If the copper

plane is not on the top surface of the circuit board,

8 to 10 vias of 0.013 inches or smaller in diameter

should be used to thermally couple the exposed-

DAP to the plane. For good thermal conduction,

the vias must be plated-through and solder-filled.

The copper plane used to conduct heat away from

the exposed-DAP should be as large as pratical. If

the plane is on the same side of the circuit board

as the exposed-DAP,2.5in is the minimum for 5V

operation into 4Ω. If the heat sink plane is buried

or not on the same side as the exposed-DAP, 5in

is the minimum for 5V operation into 4Ω. If the

ambient temperature is higher than 25°C, a larger

copper plane or forced-air cooling will be required

to keep the HM4863 junction temperature below

the thermal shutdown temperature (150°C). See

the power derating curve for the HM4863 for

derating information.

The HM4863 requires forced-air cooling when

operating into 3Ω. With the part attached to 2.5in

of exposed copper,with a 3Ω load, and with an

ambient temperature of 25°C,450 linear-feet per

minute kept the part out of thermal shutdown.

In higher ambient temperatures, higher airflow

rates and/or larger copper areas will be required

to keep the part out of thermal shutdown.

from the output pins of the HM4863. Traces from

the output of the HM4863 to the load or load

connectors should be as wide as practical.Any

resistance in the output traces will reduce the

power delivered to the load. For example, with a

4Ω load and 0.1Ω of trace resistance in each

output, output power at the load drops from 2.2W

to 2.0W

. Output power is also dependent on

supply regulation. To keep the supply voltage

from sagging under full output power conditions,

the supply traces should be as wide as practical.

Bridge Configuration Explanation

As shown in Figure 1, the HM4863 has two pairs

of operational amplifiers internally, allowing for

a few different amplifier configurations. The

first amplifier’s gain is externally configurable,

while the second amplifier is internally fixed in a

unity-gain, inverting configuration. The closed-

loop gain of the first amplifier is set by selecting

the ratio of Rf to R i while the second amplifier’s

gain is fixed by the two internal 20 kΩ resistors.

Figure 1 shows that the output of amplifier one

serves as the input to amplifier two which results

in both amplifiers producing signals identical in

magnitude, but out of phase180°.Consequently,

the differential gain for eachchannel of the IC is

AVD = 2 * (Rf/Ri)

By driving the load differentially through outputs

+OutA and −OutA or +OutB and −OutB, an

amplifier configuration commonly referred to as

“bridged mode” is established. Bridged mode

operation is different from the classical single-

ended amplifier configuration where one side of

its load is connected to ground.

3Ω & 4Ω Layout Considerations

With low impedance loads, the output power at

the loads is heavily dependent on trace resistance

HM4863

Shenzhen H&M Semiconductor Co.Ltd

http：//www.hmsemi.com

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