TDA8945S datasheet(5/21 Pages) PHILIPS

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Philips Semiconductors

TDA8945S

15 W mono BTL audio ampliﬁer

Product speciﬁcation

Rev. 02 — 7 April 2000

5 of 21

9397 750 06866

8.2.2

Headroom

Typical CD music requires at least 12 dB (factor 15.85) dynamic headroom –

compared to the average power output – for transferring the loudest parts without

distortion. At VCC =18V, RL =8 Ω and Po = 10 W at THD = 0.1% (see Figure 6), the

Average Listening Level (ALL) – music power – without any distortion yields:

Po(ALL) = 10 W/15.85 = 631 mW.

The power dissipation can be derived from Figure 11 on page 10 for 0 dB

respectively 12 dB headroom.

For the average listening level a power dissipation of 4 W can be used for a heatsink

calculation.

8.3 Mode selection

The TDA8945S has three functional modes, which can be selected by applying the

proper DC voltage to pin MODE. See Figure 4 and 5 for the respective DC levels,

which depend on the supply voltage level. The MODE pin can be driven by a 3-state

logic output stage: e.g. a microcontroller with additional components for DC-level

shifting.

Standby — In this mode the current consumption is very low and the outputs are

ﬂoating. The device is in standby mode when (VCC − 0.5 V) < VMODE <VCC, or when

the MODE pin is left ﬂoating (high impedance). The power consumption of the

TDA8945S will be reduced to <0.18 mW.

Mute — In this mode the ampliﬁer is DC-biased but not operational (no audio output);

the DC level of the input and output pins remain on half the supply voltage. This

allows the input coupling and Supply Voltage Ripple Rejection (SVRR) capacitors to

be charged to avoid pop-noise. The device is in mute mode when

3V<VMODE <(VCC − 1.5 V).

Operating — In this mode the ampliﬁer is operating normally. The operating mode is

activated at VMODE < 0.5 V.

8.3.1

Switch-on and switch-off

To avoid audible plops during supply voltage switch-on or switch-off, the device is set

to standby mode before the supply voltage is applied (switch-on) or removed

(switch-off).

The switch-on and switch-off time can be inﬂuenced by an RC-circuit on the MODE

pin. Rapid on/off switching of the device or the MODE pin may cause ‘click- and

pop-noise’. This can be prevented by proper timing of the RC-circuit on the MODE

pin.

Table 4:

Power rating as function of headroom

Headroom

Power output (THD = 0.1%)

Power dissipation (P)

0dB

Po =10W

8.5 W

12 dB

Po(ALL) = 631 mW

4 W

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