Philips TDA8559T 8. Functional description

Product data sheets Rev. 03 — 15 May 2006 5 of 36

Low-voltage stereo headphone ampliﬁer

8. Functional description

The TDA8559T contains two ampliﬁers with differential inputs, a 0.5VPoutput buffer and a

high supply voltage stabilizer. Each ampliﬁer consists of a voltage-to-current converter

(V/I), an output ampliﬁer and a common dynamic quiescent current controller. The gain of

each ampliﬁer is internally ﬁxed at 26 dB (= 20 ×). The 0.5VP output can be used as a

replacement for the single-ended capacitors. The two ampliﬁers can also be used as a

mono ampliﬁer in a BTL conﬁguration thereby resulting in more output power.

With three mode select pins, the device can be switched into the following modes:

1. Standby mode (IP<10µA)

2. Mute mode

3. Operation mode, with two input selections (the input source is directly connected or

connected via coupling capacitors at the input).

The ripple rejection in the stereo application with a single-ended capacitor can be

improved by connecting a capacitor between the 0.5VP capacitor pin and ground.

The device is fully protected against short-circuiting of the output pins to ground, to the

low supply voltage pin and across the load.

The V/I converters have a transconductance of 400 µS. The inputs are completely

symmetrical and the two ampliﬁers can be used in opposite phase. The Mute mode

causes the V/I converters to block the input signal. The input mode pin selects two

applications in which the V/I converters can be used.

The ﬁrst application (input mode pin ﬂoating) is used with a supply voltage below 6 V. The

input DC level is at ground level (the unused input pin connected to ground) and no input

coupling capacitors are necessary. The maximum converter output current is sufﬁcient to

obtain an output swing of 3 V (peak).

In the second application with a supply voltage greater than 6 V (input mode pin HIGH),

the input mode pin is connected to VP. In this conﬁguration (input DC level is

0.5VP+ 0.6 V) the input source must be coupled with a capacitor and the two unused

input pins must be connected via a capacitor to ground, to improve noise performance.

This application has a higher quiescent current, because the maximum output current of

the V/I converter is higher to obtain an output voltage swing of 9 V (peak).

The output ampliﬁers have a transresistance of 50 kΩ, a bandwidth of approximately

750 kHz and a maximum output current of 100 mA. The mid-tap output voltage equals the

voltage applied at the non-inverting pin of the output ampliﬁer. This pin is connected to the

output of the 0.5VP buffer. This reduces the distortion when the load is connected

between an output ampliﬁer and the buffer (because feedback is applied over the load).

The buffer delivers 0.5VPto the output with a maximum output (sink and source) current of

200 mA (peak).