PA4894

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

7 of 11

www.unisonic.com.tw

QW-R502-379.A

APPLICATION INFORMATION(Cont.)

Thermal Overload Protection

When the temperature of the UTC PA4894 is higher than160°C for any reasons, the thermal overload protection

function turns the amplifiers off until the temperature drop below 140°C.

The UTC PA4894 is unity gain stable and requires no external components besides gain setting resistors, an

input coupling capacitor and a proper bypassing capacitor in the typical application. Both internal amplifiers are

The differential ended amplifier has two main benefits compared to single-ended:

* The differential ended amplifier will yield 4 times larger the output power on the load at the same conditions

compared to a single ended amplifier.

* Output pins (OUTA and OUTB) are biased at the same potential VP/2, which is saving the use of an output

coupling capacitor that is required with a single ended amplifier configuration.

The differential closed loop gain of the amplifier is correlated as seen in the following ratio:

)

RMS

(

IN

)

RMS

(

O

IN

F

V

V

=

R

R

=

Avd

Output power delivered to the load is defined as follows:

L

2

)

PEAK

(

O

)

RMS

(

O

R

×

2

)

V

(

=

P

When choosing gain configuration to obtain the desired output power, check that the amplifier is not current

limited or clipped.

The maximum current which can be delivered to the load is 500mA

L

)

PEAK

(

O

)

PEAK

(

O

R

V

=

I

closed−loop gain of both amplifiers, it is critical to choose both of them.

The low gain configuration minimizes THD + noise values and maximizes the signal to noise ratio, and the

amplifier can still be used without running into the bandwidth limitations.

A closed loop gain in the range from 2 ~ 5 is recommended to optimize overall system performance.

The input coupling capacitor blocks the DC voltage at the amplifier input terminal. A high−pass filter is generated

by this capacitor and Rin, and the cut−off frequency is defined by the following fomula:

IN

IN

C

C

×

R

×

π

×

2

1

=

f

The size of the capacitor must be large enough to couple in low frequencies without severe attenuation.

However a large input coupling capacitor requires more time to reach its quiescent DC voltage (VP/2) and can

increase the turn−on pops.

An input capacitor value between 0.1μ and 0.39μF is sugguested in most applications.

To avoid the pop noise, the bapass capacitor should be chosen prompty. The bypass capacitor determines the

rate at which this device starts and it provides half−supply filtering.

1.0μF bypassing capacitor is recommended to be used.