TFA9842J/N1,112 Datasheet TFA9842J/N1,112 | P4-P6

Philips Semiconductors

TFA9842J

2-channel audio ampliﬁer (2 x SE or 1 x BTL)

Preliminary data Rev. 01 — 26 April 2004 4 of 21

9397 750 12013

7.2 Pin description

8. Functional description

8.1 Input conﬁguration

The input cut-off frequency is:

(1)

SE application: R

=60kΩ and C

= 220 nF:

(2)

BTL application: R

=30kΩ and C

= 470 nF:

(3)

As shown in Equation 2 and Equation 3, large capacitor values for the inputs are not

necessary, so the switch-on delay during charging of the input capacitors can be

minimized. This results in a good low frequency response and good switch-on

behavior.

8.2 Power ampliﬁer

The power ampliﬁer is a Single-Ended (SE) and/or Bridge-Tied Load (BTL) ampliﬁer

with an all-NPN output stage, capable of delivering a peak output current of 3 A.

Using the TFA9842J as a BTL ampliﬁer offers the following advantages:

• Lower peak value of the supply current

Table 3: Pin description

Symbol Pin Description

IN2+ 1 input 2

OUT2− 2 inverted loudspeaker terminal 2

CIV 3 common input voltage decoupling

IN1+ 4 input 1

GND 5 ground

SVR 6 half supply voltage decoupling (ripple rejection)

MODE 7 mode selection input (standby, mute and operating)

OUT1+ 8 non inverted loudspeaker terminal 1

9 supply voltage

TAB - back side tab or heats spreader has to be connected to ground

i cut off–()

2π R

×()

-----------------------------

i cut off–()

2π 60 10

× 220× 10

9–

×()

-----------------------------------------------------------------

12 Hz==

i cut off–()

2π 30 10

× 470× 10

9–

×()

-----------------------------------------------------------------

11 Hz==

Philips Semiconductors

TFA9842J

2-channel audio ampliﬁer (2 x SE or 1 x BTL)

Preliminary data Rev. 01 — 26 April 2004 5 of 21

9397 750 12013

• Ripple frequency on the supply voltage is twice the signal frequency

• No expensive DC-blocking capacitor

• Good low frequency performance.

8.2.1 Output power measurement

The output power as a function of the supply voltage is measured on the output pins

at THD = 10 %; see Figure 6.

The maximum output power is limited by the supply voltage of 26 V and the maximum

available output current is 3 A (repetitive peak current). A minimum load for SE of 4 Ω

and for BTL of 16 Ω is required for V

> 22 V; see Figure 5.

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 V

= 18 V and P

= 5 W (SE with R

=4Ω) or P

= 10 W (BTL with

=8Ω) at THD = 0.2 % (see Figure 7), the Average Listening Level (ALL) music

power without any distortion yields:

(4)

(5)

The power dissipation can be derived from Figure 9 (SE and BTL) for a headroom of

0 dB and 12 dB, respectively (see Table 4).

For the average listening level a power dissipation of 4.2 W can be used for a

heatsink calculation.

8.3 Mode selection

The TFA9842J has three functional modes, which can be selected by applying the

proper DC voltage to pin MODE (see Tabl e 5 and Figure 3).

Table 4: Power rating as function of headroom

Headroom Power output Power dissipation

(both channels driven)

SE BTL

0dB P

=5W P

=10W P

= 8.4 W

12 dB P

o(ALL)

= 315 mW P

o(ALL)

= 630 mW P

= 4.2 W

oALLSE,()

510

⋅

15.85

---------------

315 mW==

o ALL BTL,()

10 10

⋅

15.85

------------------

630 mW==

Table 5: Mode selection

MODE

Ampliﬁers 1 and 2

0 to 0.8 V standby

4.5 V to (V

− 3.5 V) mute

− 2.0 V) to V

Philips Semiconductors

TFA9842J

2-channel audio ampliﬁer (2 x SE or 1 x BTL)

Preliminary data Rev. 01 — 26 April 2004 6 of 21

9397 750 12013

Standby — The current consumption is very low and the outputs are ﬂoating. The

device is in standby mode when V

MODE

< 0.8 V, or when pin MODE is grounded.

Mute — The ampliﬁer is DC-biased but not operational (no audio output). This allows

the input coupling capacitors to be charged to avoid pop-noise. The device is in mute

mode when 4.5V<V

MODE

<(V

− 3.5 V).

On — The ampliﬁer is operating normally. The operating mode is activated at

MODE

>(V

− 2.0 V).

8.4 Supply voltage ripple rejection

The supply voltage ripple rejection (SVRR) is measured with an electrolytic capacitor

of 150 µF on pin SVR using a bandwidth of 20 Hz to 22 kHz. Figure 11 illustrates the

SVRR as function of the frequency. A larger capacitor value on pin SVR improves the

ripple rejection behavior at the lower frequencies.

8.5 Built-in protection circuits

The TFA9842J contains two types of temperature sensors; one measures local

temperatures of the power stages and one measures the global chip temperature. At

a local temperature of the power stage of approximately 185

C or a global

temperature of approximately 150

C this detection circuit switches off the power

stages for 2 ms. High impedance of the outputs is the result. After this time period the

power stages switch on automatically and the detection will take place again; still a

too high temperature switches off the power stages immediately. This protects the

TFA9842J against shorts to ground, to the supply voltage, across the load and too

high chip temperatures.

The protection will only be activated when necessary, so even during a short-circuit

condition, a certain amount of (pulsed) current will still be ﬂowing through the short,

just as much as the power stage can handle without exceeding the critical

temperature level.

Fig 3. Mode selection.

MCE502

standby all mute 1/2 on

0.8 4.5 V

−3.5 V

MODE

(V)

−2.0

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TFA9842J/N1,112

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IC AMP AUDIO PWR 15W STER 9SIL

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