FAN7040
9
Typical Application Information
Functional Description
The FAN7040 is a mono BTL output amplifier with DC volume control. It is designed for use in TVs and monitors but is also
suitable for battery-fed portable recorders and radios.
In conventional DC volume circuits the control or input stage is AC-coupled to the output stage via external capacitors to keep
the offset voltage low. In the FAN7040 the DC volume control stage is integrated into the input stage so that no coupling
capacitors are required. With this configuration, a low offset voltage is still maintained and the minimum supply voltage
remains low.
The BTL principle offers the following advantages:
•Lower peak value of the supply current
•The frequency of the ripple on the supply voltage is twice the signal frequency.
Consequently, a reduced power supply with smaller capacitors can be used which also results in cost reductions. For portable
applications there is a trend to decrease the supply voltage, resulting in a reduction of output power at conventional output
stages. Using the BTL principle increases the output power. The maximum gain of the amplifier is fixed at 37dB. The DC vol-
ume control stage has a logarithmic control characteristic. The total gain can be controlled from 37dB to -52dB. If the DC vol-
ume control voltage is below 0.3V, the device switches to the mute mode. The amplifier is short-circuit proof to ground, Vcc
and across the load. A thermal protection circuit is also implemented. If the crystal temperature rises above +150°C the TSD is
operated, thereby the output power is off. Special attention is given to switch-on and switch-off clicks, low HF radiation and a
good overall stability.
Voltage Gain
The maximum closed-loop voltage gain has been internally fixed at 37dB.
Output Power
The output power as a function of supply voltage has been measured at THD=10%. The maximum output power is limited by
the maximum allowed power dissipation at Ta=25°C approximately 1.8W, and the maximum available output current is 1.25A
repetitive peak current.
Short Circuit Protection
The output (pins 14 and 17) can be short-circuited to ground respectively to +VDD. The Missing Current Limiter(MCL) pro-
tection circuit will shut-off the amplifier. Removing the short-circuit will reset the amplifier automatically. Short-circuit across
the load(pins 14 and 17) will activate the thermal protection circuit; this will result in thermal shutdown protection.
For single-end application the output peak current may not exceed 130mA; at higher output currents the short circuit protec-
tion(MCL) will be activated.
Power Dissipation
Power dissipation is a major concern when designing any power amplifier and must be thoroughly understood to ensure a suc-
cessful design. Equation (1) states the maximum power dissipation point for a bridged amplifier operating at a given supply
voltage and driving a specified output load.
Since the FAN7040 is driving a bridged amplifier, the internal maximum power dissipation point of the FAN7040 results from
equation (1). Even with the large internal power dissipation, the FAN7040 does not require heat sinking over a wide range of
ambient temperature. From equation (1), assuming a 12V power supply and a 16Ω load, the maximum power dissipation point
is 1.8W. The maximum power dissipation point obtained from equation (1) must not be greater than the power dissipation that
results from equation (2) :
For package 20SOP, R
thja
=70°C/W, T
JMAX
=150°C for the FAN7040.
P
DMAX
4
V
CC
2
2π
2
R
L
-----------------
⋅=
(1)
P
DMAX
T
JMAX
T
A
–()
R
thja
----------------------------------=
(2)
