SA7265 Datasheet, PDF (5/11 Pages) Silan Microelectronics Joint-stock – 2CH AUDIO POWER AMPLIFIER(25W X2)

SA7265
BRIDGE APPLICATION
Another application suggestion concerns the BRIDGE configuration, where the two power amplifiers are
connected as shown by the schematic diagram of the following.
This application shows, however, some operative limits due to dissipation and current capability of the output
stage. For this reason, we recommend to use the SA7265 in bridge with the supply voltage equal/lower than
±16V when the load is 8Ω; with higher loads (i.e.16Ω), the amplifier can work correctly in the whole supply
voltage range.
With R1=8Ω, Vs=±16V the maximum output power obtainable is 50W at TDH=10%. The quiescent current
remains unchanged with respect to the stereo configuration (~80mA as typical at Vs=±16V).
The last point to take into consideration concerns the short-circuit protection. As for the stereo application, the
SA7265 is fully protected against any kind of short-circuit (between Out/Gnd, Out/+Vs and Out/-Vs).
Power Dissipation and Heat Sinking
The SA7265 must always be operated with a heat sink, even when it is not required to drive a load. The idling
current of the device is 80mA, so that on a ±20V power supply an unloaded SA7265 must dissipate about 3W of
power. The 54°C/W junction-to-ambient thermal resistance of a HSIP-11 package would cause the die
temperature to rise 162°C above ambient, so the thermal protection circuitry will shut the amplifier down if
operation without a heat sink is attempted.
In order to determine the appropriate heat sink for a given application, the power dissipation of the SA7265 in
that application must be known. When the load is resistive, the maximum average power that the IC will be
required to dissipate is approximately:
PD(MAX)=Vs²/π²RL+PQ
Where VS is the total power supply voltage across the SA7265, RL is the load resistance PQ is the quiescent
power dissipation of the amplifier. The above equation is only an approximation which assume an “ideal”class B
output stage and constant power dissipation in all other parts of the circuit. The curves of “Power Dissipation vs.
Power Output”give a better representation of the behaviour of the SA7265 with various power supply voltages
and resistive loads. As an example, if the SA7265 is operated on a ±20V power supply with a resistive load of 8Ω,
it can develop up to 23W of internal power dissipation. If the die temperature is to remain below 150°C for
ambient temperatures up to 50°C, the total junction-to-ambient thermal resistance must be less than:
(150°Cˉ50°C)/23W˙4.3°C/W
Using Rth(j-c) = 2°C /W, the sum of the case-to-heat-sink interface thermal resistance and the heat-sink-to-
ambient thermal resistance must be less than 2.3°C/W. The case-to-heat-sink thermal resistance of the HSIP-11
package varies with the mounting method used. A metal-to-metal interface will be about 1°C /W if lubricated, and
about 1.2°C /W if dry.
If a mica insulator is used, the thermal resistance will be about 1.6°C /W lubricated and 3.4°C /W dry. For this
example, we assume a lubricated mica insulator between the SA7265 and the heat sink. The heat sink thermal
resistance must then be less than:
4.3°C/W-2°C/W-1.6°C/W˙0.7°C/W
This is a rather large heat sink and may not be practical in some applications. If a smaller heat sink is required
for reasons of size or cost, there is an alternative. The heat sink can be isolated from the chassis so the mica
washer is not needed. This will change the required heat sink to a 1.3°C /W unit if the case-to-heat-sink interface
is lubricated.
The thermal requirements can become more difficult when an amplifier is driving a reactive load. For a given
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http: www.silan.com.cn
REV:1.2 2006.05.25
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