CM8662IP Champion Microelectronic Corp., CM8662IP Datasheet - Page 5

• Manufacturer Part Number: CM8662IP
• Description: Audio amplifier, Single channel, PDIP, 8-Pin
• Manufacturer: Champion Microelectronic Corp.

APPLICATION INFORMATION
Bridge Configuration Explanation
As shown in Figure 1, the CM8662 has two operational
amplifiers internally, allowing for a few different amplifier
configuration. The first amplifier's gain is externally
configurable, while the second amplifier is internally fixed in a
unity-gain, inverting configuration. The closed-loop gain of the
first amplifier is set by selecting the ratio of R
second amplifier's gain is fixed by the two internal 10kΩ
resistors. Figure 1 shows that the output of amplifier one
serves as the input to amplifier two which results in both
amplifiers producing signals identical in magnitude, but out of
phase 180 ° . Consequently, the differential gain for the IC is
By dividing the load differentially through output V
and amplifier configuration commonly referred to as "bridged
mode" is established. Bridged mode operation is different from
the classical single-ended amplifier configuration where one
side of the load is connected to ground.
A bridge amplifier design has a few distinct advantages over
the single-ended configuration, as it provides differential drive
to the load, thus doubling output swing for a specified supply
voltage. Consequently, four times the output power is possible
as compared to a single-ended amplifier under the same
conditions. This increase in attainable output power assumes
that the amplifier is not current limited or clipped. In order to
choose an amplifier's closed-loop gain without causing
excessive clipping which will damage high frequency
transducers used in loudspeaker systems, please refer to the
Audio Power Amplifier Design section.
A bridge configuration, such as the one used in CM8662, also
creates a second advantage over single-ended amplifier.
Since the differential outputs, V
half-supply, no net DC voltage exists across the load. This
eliminates the need for an output coupling capacitor which is
required in a single supply, single-ended amplifier
configuration. Without an output coupling capacitor, the
half-supply bias across the load would result in both increased
internal IC power dissipation and also permanent loudspeaker
damage.
Power Dissipation
Power dissipation is a major concern when designing a
successful amplifier, whether the amplifier is bridged or
single-ended. A direct consequence of the increased power
delivered to the load by a bridge amplifier is an increase in
internal power dissipation. Equation 1 states the maximum
power dissipation point for a bridge amplifier operating at a
given supply voltage and driving a specified output load.
Since the CM8662 has two operational amplifiers in one
package, the maximum internal power dissipation is 4 times
that of a single-ended amplifier. Even with this substantial
increase in power dissipation, the CM8662 does not require
heatsinking. From Equation 1, assuming a 5V power supply
and an 8Ω load, the maximum power dissipation point is
625mW. The maximum power dissipation point obtained from
Equation 1 must not be greater than the power dissipation that
results from Equation 2:
2002/01/31
P
Preliminary
DMAX
P
DMAX
= 4*(V
= (T
A
VD
JMAX
DD
)
= 2*(R
2
-T
/(2π
o1
A
)/Θ
and V
2
f
Rev. 2
/R
R
JA
L
i
)
)
o2
, are biased at
f
(2)
to R
(1)
Champion Microelectronic Corporation
o1
i
A
while the
and V
UDIO
o2
,
P
OWER
For package M08A, Θ
JA
ambient temperature, T
Equation 2 can be used to find the maximum internal power
dissipation supported by the IC packaging. If the result of
Equation 1 is greater than that of Equation 2, then wither the
supply voltage must be decreased, the load impedance
increased, or the ambient temperature reduced. For the typical
application of a 5V power supply, with an 8Ω load, the
maximum ambient temperature possible without violating the
maximum junction temperature is approximately 44℃
provided that device operation is around the maximum power
dissipation point. Power dissipation is a function of output
power and thus, if typical operation is not around the
maximum power dissipation point, the ambient temperature
can be increased. Refer to the Typical Performance
Characteristics curves for power dissipation information for
lower output powers.
Power Supply Bypassing
As with any power amplifier, proper supply bypassing is critical
for low noise performance and high power supply rejection.
The capacitor location on both the bypass and power supply
pins should be as close to the device as possible. As
displayed in the Typical Performance Characteristics
section, the effect of a larger half supply bypass capacitor is
improved PSSR due to increased half-supply stability. Typical
applications employ a 5V regulator with 10μF and a 0.1μF
bypass capacitors which aid in supply stability, but do not
eliminate the need for bypassing the supply nodes of the
CM8662. The selection of bypass capacitors, especially C
thus dependant upon desired PSSR requirements, click and
pop performance as explained in the section, Proper Selection
of External Components, system cost, and size constraints.
Shutdown Function
In order to reduce power consumption while not in use, the
CM8662 contains a shutdown pin to externally turn off the
amplifier's bias circuitry. The shutdown feature turns the
amplifier off when a logic high is placed on the shutdown pin.
The trigger point between a logic low and logic high level is
typically half supply. It is best to switch between ground and
supply to provide maximum device performance. By switching
the shutdown pin to V
be minimized in idle mode. While the device will be disabled
with shutdown pin voltage less than V
be greater than the typical value of 0.7μA. In either case, the
shutdown pin should be tied to a definite voltage because
leaving the pin floating may result in an unwanted shutdown
condition.
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry which provides
a quick, smooth transition into shutdown. Another solution is to
use a single-pole, single-throw switch that when closed, is
connected to ground and enables the amplifier. If the switch is
open, then a soft pull-up resistor of 47 kΩ will disable the
CM8662. There are no soft pull-up resistors inside the
CM8662, so a definite shutdown pin voltage must be applied
externally, or the internal logic gate will be left floating which
could disable the amplifier unexpectedly.
= 107℃/W. T
AMP. with S
JMAX
=150℃ for the CM8662. Depending on the
DD
JA
A
, the CM8662 supply current draw will
, of the system surroundings,
= 170℃/W and for package N08E, Θ
HUTDOWN
DD
, the idle current may
CM8662
Page 5
M
ODE
B
, is