TFA9842AJ/N1,112 Datasheet TFA9842AJ/N1,112 | P4-P6

Preliminary speciﬁcation Rev. 01 — 28 April 2006 4 of 18

Philips Semiconductors

TFA9842AJ

7.5 W stereo power ampliﬁer with volume control

7.2 Pin description

8. Functional description

8.1 Input conﬁguration

The input cut-off frequency is:

(1)

Single-ended application: R

=60kΩ and C

= 220 nF:

(2)

As shown in Equation 2, large capacitor values for the inputs are not necessary; therefore

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.

The TFA9842AJ has clamps on the inputs. In Standby mode the voltage on the input pins

is clamped for voltages lower than −0.1 V. When the TFA9842AJ is in Mute, Volume

control or Operating mode (maximum gain) the input clamp voltage is 1 V (RMS).

8.2 Power ampliﬁer

The power ampliﬁer is a single-ended ampliﬁer with an all NPN output stage, capable of

delivering a peak output current of 3 A.

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%;seeFigure 7. 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 of 3 Ω is required for supply voltages > 22 V; see Figure 4. The output power is

measured with one channel driven.

Table 3. Pin description

Symbol Pin Description

IN2 1 input 2

OUT2 2 loudspeaker terminal 2

CIV 3 common input voltage decoupling

IN1 4 input 1

GND 5 ground

SVR 6 half supply voltage decoupling (ripple rejection)

VC 7 volume control input (standby, mute and volume control)

OUT1 8 loudspeaker terminal 1

9 supply voltage

i 3dB–()

2π R

×()

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

i 3dB–()

2π 60 10

× 220× 10

9–

×()

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

12 Hz==

Preliminary speciﬁcation Rev. 01 — 28 April 2006 5 of 18

Philips Semiconductors

TFA9842AJ

7.5 W stereo power ampliﬁer with volume control

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

= 17 V and P

= 5 W (SE with R

=4Ω) at THD < 0.5 % (see Figure 5), the Average

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

(3)

The power dissipation can be derived from Figure 8 (SE) for 0 dB respectively 12 dB

headroom (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 TFA9842AJ has four functional modes, which can be selected by applying the proper

DC voltage to pin VC (see Table 5).

8.4 Supply voltage ripple rejection

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

150 µF connected to pin SVR with a bandwidth of 20 Hz to 22 kHz. The SVRR as a

function of the frequency is illustrated in Figure 10. A larger capacitor value on pin SVR

improves the ripple rejection behavior at the lower frequencies.

Table 4. Power rating as function of headroom

Headroom Power output SE

(THD < 0.5 %)

Power dissipation (P);

both channels driven

0dB P

= 5 W 8.4 W

12 dB P

o(ALL)

= 315 mW 4.2 W

oALL()

15.85

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

315 mW==

Table 5. Mode selection

I(VC)

Status Deﬁnition

0 V to 0.8 V Standby in this mode the current consumption is very low

and the outputs are ﬂoating; the device is in

Standby mode when V

I(VC)

< 0.8 V.

1.2 V to 1.5 V Mute in this mode 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

1.2 V < V

I(VC)

< 1.5 V.

1.5 V to 5.0 V Volume control in this mode the volume of the ampliﬁer can be

controlled; the gain can be adjusted between the

range of 1.5 V < V

I(VC)

< 5.0 V.

5.0 V to V

On (maximum gain) in this mode the ampliﬁer has its maximum gain;

the Operating mode is activated at V

I(VC)

> 5.0 V.

Preliminary speciﬁcation Rev. 01 — 28 April 2006 6 of 18

Philips Semiconductors

TFA9842AJ

7.5 W stereo power ampliﬁer with volume control

8.5 Built-in protection circuits

The TFA9842AJ contains two types of temperature sensors; one measures the 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. When

the outputs are switched off the voltage is measured on the outputs. In the event of a

short-circuit to ground or to V

the device will remain in Protection mode. In all other

cases the power stages switch-on automatically and the detection will take place again;

however a too high temperature will switch-off the power stages immediately. This can

result in repetitive switching during too high junction temperature. This protects the

TFA9842AJ against short-circuits 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 ﬂow through the short-circuit (as

much as the power stage can handle without exceeding the critical temperature level).

9. Limiting values

10. Thermal characteristics

Table 6. Limiting values

In accordance with the Absolute Maximum Rating System (IEC 60134).

Symbol Parameter Conditions Min Max Unit

supply voltage operating −0.3 +28 V

input voltage −0.3 V

+ 0.3 V

ORM

repetitive peak output

current

-3 A

stg

storage temperature non-operating −55 +150 °C

amb

ambient temperature operating −40 +85 °C

tot

total power dissipation - 35 W

CC(scp)

short-circuit protection

supply voltage

-26V

Table 7. Thermal characteristics

Symbol Parameter Conditions Typ Unit

th(j-a)

thermal resistance from junction to ambient in free air 40 K/W

th(j-c)

thermal resistance from junction to case both channels driven 2.0 K/W

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TFA9842AJ/N1,112

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IC AMP AUDIO PWR 7.5W STER 9SIL

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