2 x 7 W stereo Bridge Tied Load (BTL) audio amplifier
Rev. 02 — 14 February 2000Product specification
1.General description
The TDA8944J is a dual-channel audio power amplifier with an output power of
2 × 7 W at an 8 Ω load and a 12 V supply. The circuit contains two Bridge Tied Load
(BTL) amplifierswith an all-NPN output stage and standby/mutelogic. The TDA8944J
comes in a 17-pin DIL-bent-SIL (DBS) power package. The TDA8944J is
printed-circuit board (PCB) compatible with all other types in the TDA894x family.
One PCB footprint accommodates both the mono and the stereo products.
2.Features
■ Few external components
■ Fixed gain
■ Standby and mute mode
■ No on/off switching plops
■ Low standby current
■ High supply voltage ripple rejection
■ Outputs short-circuit protected to ground, supply and across the load
n.c.13not connected
OUT2−14negative loudspeaker terminal 2
GND215ground channel 2
V
CC2
OUT2+17positive loudspeaker terminal 2
8.Functional description
The TDA8944J is a stereo BTL audio power amplifier capable of delivering 2 × 7W
output power to an 8 Ω load at THD = 10%, using a 12 V power supply and an
external heatsink. The voltage gain is fixed at 32 dB.
With the three-level MODE input the device can be switched from ‘standby’ to ‘mute’
and to ‘operating’ mode.
The TDA8944J outputs are protected by an internal thermal shutdown protection
mechanism and a short-circuit protection.
8.1 Input configuration
The TDA8944J inputs can be driven symmetrical (floating) as well as asymmetrical.
In the asymmetrical mode one input pin is connected via a capacitor to the signal
ground which should be as close as possible to the SVR (electrolytic) capacitor
ground. Note that the DC level of the input pins is half of the supply voltage VCC, so
coupling capacitors for both pins are necessary.
As shown in Equation 1 and 2, 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
behaviour.
Remark: TopreventHF oscillations do not leave the inputs open, connect a capacitor
of at least 1.5 nF across the input pins close to the device.
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Product specificationRev. 02 — 14 February 20004 of 21
The power amplifier is a Bridge Tied Load (BTL) amplifier with an all-NPN output
stage, capable of delivering a peak output current of 2 A.
The BTL principle offers the following advantages:
•
•
•
•
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 8. The maximum output power is limited by the maximum
supply voltage of 12 V and the maximum available output current: 2 A repetitive peak
current.
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=12V, RL=8Ω and Po= 4 W at THD = 0.1% (see Figure 6), the
Average Listening Level (ALL) – music power – without any distortion yields:
P
TDA8944J
2 x 7 W stereo BTL audio amplifier
Lower peak value of the supply current
The ripple frequency on the supply voltage is twice the signal frequency
No expensive DC-blocking capacitor
Good low frequency performance.
= 4 W/15.85 = 252 mW.
o(ALL)
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 TDA8944J 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) < V
the MODE pin is left floating (high impedance). The power consumption of the
TDA8944J will be reduced to <0.18 mW.
MODE<VCC
, or when
9397 750 06861
Product specificationRev. 02 — 14 February 20005 of 21
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<V
Operating — In this mode the amplifier is operating normally. The operating mode is
activated at 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.
<(VCC− 1.5 V).
MODE
MODE
TDA8944J
2 x 7 W stereo BTL audio amplifier
< 0.5 V.
8.4 Supply Voltage Ripple Rejection (SVRR)
The SVRR is measured with an electrolytic capacitor of 10 µF on pin SVR at a
bandwidth of 10 Hz to 80 kHz. Figure 13 on page 11 illustrates the SVRR as function
of the frequency. A larger capacitor value on the SVR pin improves the ripple rejection
behaviour at the lower frequencies.
8.5 Built-in protection circuits
The TDA8944J contains two types of protection circuits, i.e. short-circuit and thermal
shutdown.
8.5.1 Short-circuit protection
Short-circuit to ground or supply line — This is detected by a so-called ‘missing
current’ detection circuit which measures the current in the positive supply line and
the current in the ground line. A difference between both currents larger than 0.4 A,
switches the power stage to standby mode (high impedance).
Short-circuit across the load — This is detected by an absolute-current
measurement. An absolute-current larger than 2 A, switches the power stage to
standby mode (high impedance).
8.5.2 Thermal shutdown protection
The junction temperature is measured by a temperature sensor; at a junction
temperature of approximately 150 °C this detection circuit switches the power stage
to standby mode (high impedance).
9397 750 06861
Product specificationRev. 02 — 14 February 20006 of 21