APA2068
Application Descriptions (Cont.)
Optimizing Depop Circuitry (Cont.)
Maximum Output Swing Clamping Function
(VolMax)
constant can be relatively large. To reduce transients
in SE mode, an external 1kW resistor can be placed in
parallel with the internal 10kW resistor. The tradeoff
for usingthisresistor isanincreaseinquiescent current.
In the most cases, choosing a small value of Ci in the
range of 0.33mF to 1mF, Cb being equal to 4.7mF and
an external 1kW resistor should be placed in parallel
with the internal 10kW resistor should produce a
virtually clickless and popless turn-on.
The APA2068 provide the maximum output swing
clamping function to protect the speaker.
When input a non-zero voltage (Vx) to VolMax pin,
the amplifier’s output amplitude (Vo) is be limited at
Vo = Vdd –Vx. This function can effective to limited
the output power across the speaker, and avoid
damaging the speaker.
The maximum setting voltageof VolMax isVdd/2, and
when this function is not used, place the VolMax
connect to GND.
A high gain amplifier intensifies the problem as the
small delta in voltage is multiplied by the gain. So it
is advantageous to use low-gain configurations.
BTL Amplifier Efficiency
Shutdown Function
An easy-to-use equation to calculate efficiency starts
out asbeing equal to the ratio of power from the power
supply to the power delivered to the load.
Inorder to reducepower consumption while not in use,
the APA2068 contains a shutdown pin to externally
turn off the amplifier bias circuitry. This shutdown
featureturnsthe amplifier off when alogiclowisplaced
on the SHUTDOWN pin. The trigger point between a
logic high and logic low level is typically 2.0V. It is
best to switch between ground and the supply VDD to
providemaximum deviceperformance.
The following equations are the basis for calculating
amplifier efficiency.
PO
PSUP
(9)
Efficiency =
Where :
PO =
VORMS ´ VORMS
VP´ VP
2RL
=
By switching the SHUTDOWNpin to low, the amplifier
enters a low-current state, IDD<1mA. APA2068 is in
shutdown mode, except PC-BEEP detect circuit.
On normal operating, SHUTDOWN pin pull to high
level to keeping the IC out of the shutdown mode.
The SHUTDOWN pin should be tied to a definite
voltage to avoid unwanted state changes.
R L
VP
Ö2
(10)
(11)
VORMS =
2VP
pRL
PSUP = VDD x IDDAVG = VDD x
Efficiency of a BTL configuration :
PO
PSUP
pVP
4VDD
2VP
pRL
VPxVP ) / (VDD x
2RL
) =
(12)
(
Mute Function
=
TheAPA2068 mutes the amplifier outputs when logic
high is applied to the MUTE pin. Applying logic low to
the MUTE pin returns the APA2068 to normal
operation. Prevent unanticipated mute behavior by
connecting the Mute pin to logic high or low. Do not
let the Mute pin float.
Table 1 calculates efficiencies for four different output
powerlevels.
Note that the efficiency of the amplifier is quite low for
lower power levels and rises sharply as power to the
Copyright ã ANPEC Electronics Corp.
21
www.anpec.com.tw
Rev. A.2 - Jul., 2005
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
