Agamem AA4838 Audio power amplifier Datasheet

Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
■ DESCRIPTION
The AA4838 is a monolithic integrated circuit that provides DC volume control, and stereo
bridged audio power amplifiers capable of producing 2W into 4Ωwith less than 1.0% THD or
2.2W into 3 Ω with less than 1.0% THD. The audio integrated circuits were designed
specifically to provide high quality audio while requiring a minimum amount of external
components. The AA4838 incorporates a DC volume control, stereo bridged audio power
amplifiers and a selectable gain or bass boost, making it optimally suited for multimedia
monitors, portable radios, and desktop and portable computer applications. The AA4838
features an externally controlled, low-power consumption shutdown mode, and both a power
amplifier and headphone mute for maximum system flexibility and performance.
■ FEATURES
• DC volume control interface.
• System beep detects.
• Stereo switchable bridged/single-ended power amplifiers
• Selectable internal/external gain or bass boost
• “Click and pop” suppression circuitry
• Thermal shutdown protection circuitry
■ APPLICATIONS
• Portable and desktop computers
• Multimedia monitors
• Portable radios, PDAs, and portable TVs
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DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
■ BLOCK DIAGRAM
■ PIN DESCRIPTION
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DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
Agamem Microelectronics Inc.
PRELIMINARY
PIN NO
AA4838
AUDIO POWER AMPLIFIER
PIN NAME
FUNCTION
1,8,14,20,23
GND
2
SHUTDOWN
3
GAIN SELECT
4
MODE
Output stage control(BTL/SE)
5
MUTE
Mute function control
6,16,27
VDD
7
DC VOL
9
RIGHT DOCK
10
RIGHT IN
Right audio input
11
BEEP IN
Beep input
12
LEFT IN
Left audio input
13
LEFT DOCK
Left Dock
15
LEFT OUT+
Positive left audio output
17
LEFT OUT-
Negative left audio output
18
LEFT GAIN 2
External left gain control pin2
19
LEFT GAIN 1
External left gain control pin1
21
HP SENSE
22
BYPASS
24
RIGHT GAIN 1
External right gain control pin1
25
RIGHT GAIN 2
External right gain control pin2
26
RIGHT OUT-
Negative left audio output
28
RIGHT OUT+
Positive left audio output
©Copyright Agamem Microelectronics Inc.
Supply ground
Shutdown function control
Gain selection(internal gain/external gain)
Supply voltage
DC volume control(fixed/or adjustable)
Right dock
Headphone sense
Bypass voltage
3
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DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
■ ABSOLUTE MAXIMUM RATINGS
(TA = +25°C)
PARAMETER
SYMBOL
RATING
UNIT
Power supply voltage
VCC
6
V
Storage temperature
Tstg
–65 ~+150
°C
Input voltage
VIN
–0.3 ~VDD+0.3
V
Power dissipation
PD
Internally limited
mW
ESD susceptibility
HBM
2000
V
WARNING: Semiconductor devices can be permanently damaged by application of stress (voltage, current,
temperature, etc.) in excess of absolute maximum ratings. Do not exceed these ratings.
■ ELECTRICAL CHARACTERISTICS FOR ENTIRE IC
The following specifications apply for VDD = 5V unless otherwise noted. Limits apply for TA = 25˚C
PARAMETER
Supply Voltage
Quiescent Power
Supply Current
Shutdown Current
Headphone Sense
High Input Voltage
Headphone Sense
Low Input Voltage
SYMBOL
TEST CONDITION
VDD
IDD
VIN= 0V, IO= 0A
ISD
Vshutdown = VDD
VALUE
MIN TYP MAX
2.7
5.5
-
UNIT
V
15
30
mA
0.7
2.0
μA
VIH
4
-
-
V
VIL
-
-
0.8
V
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TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. AGAMEM DOES NOT ASSUME ANY
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DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
■ ELECTRICAL CHARACTERISTICS FOR VOLUME ATTENUATORS
The following specifications apply for VDD = 5V unless otherwise noted. Limits apply for TA = 25˚C
PARAMETER
SYMBOL
TEST CONDITION
Attenuator
Range
CRANGE
Gain with VDCVOL = 5V, No
Load
Attenuation with VDCVOL
= 0V (BM & SE)
VMUTE = 5V, Bridged Mode
(BM)
VMUTE = 5V, Single-Ended
Mode (SE)
Mute
Attenuation
AM
VALUE
MIN TYP MAX
-
-
±0.75
-75
-
-
-78
-
-
-78
-
-
UNIT
dB
dB
dB
dB
■ ELECTRICAL CHARACTERISTICS FOR SINGLE-ENDED MODE OPERATION
The following specifications apply for VDD = 5V unless otherwise noted. Limits apply for TA = 25˚C
PARAMETER
SYMBOL
Output
Power
PO
Total
Harmonic
Distortion+
Noise
Power Supply
Rejection
Ratio
THD+N
Signal to
Noise Ratio
Channel
Separation
SNR
PSRR
XTALK
TEST CONDITION
THD = 1.0%; f = 1kHz; RL =
32Ω
THD = 10%; f = 1 kHz; RL=
32Ω
VOUT = 1VRMS, f=1kHz, RL
= 10kΩ, AVD = 1
CB = 1.0 µF,f=120Hz,
VRIPPLE
=200mVrms
POUT =75 mW, RL = 32Ω,
A-Wtd Filter
f=1kHz, CB = 1.0 µF
©Copyright Agamem Microelectronics Inc.
5
MIN
VALUE
TYP MAX
UNIT
-
85
-
mW
-
95
-
mW
-
0.065
-
-
58
-
dB
-
102
-
dB
-
65
-
dB
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DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
■ ELECTRICAL CHARACTERISTICS FOR BRIDGED MODE OPERATION
The following specifications apply for VDD = 5V unless otherwise noted. Limits apply for TA = 25˚C
PARAMETER
Output Offset
Voltage
Output Power
SYMBOL
TEST CONDITION
VOS
VIN = 0V, No Load
PO
THD+N=1.0%; f=1kHz; RL=3Ω
THD+N=1.0%; f=1kHz; RL=4Ω
THD=1% (max);f=1 kHz;
RL= 8Ω
VALUE
MIN TYP MAX
UNIT
-
5
±50
mV
-
2.2
2
-
W
W
1.0
1.1
-
W
THD+N=10%;f=1 kHz; RL= 8Ω
-
1.5
-
W
PO = 1W, 20 Hz< f < 20
kHz,RL=8Ω, AVD=2
PO=340 mW, RL = 32Ω
-
0.3
-
-
1.0
-
%
-
74
-
dB
-
93
-
dB
-
70
-
Total
Harmonic
Distortion+
Noise
THD+N
Power Supply
Rejection
Ratio
Signal to
Noise Ratio
PSRR
CB=1.0 µF, f=120 Hz,
VRIPPLE=200 mVrms; RL=8Ω
SNR
Channel
Separation
XTALK
VDD=5V, POUT=1.1W,
RL=8Ω, A-Wtd Filter
f=1kHz, CB=1.0 µF
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2008/8/26
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DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
■ TYPICAL APPLICATION
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Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
■ TRUTH TABLE FOR LOGIC INPUTS (Note)
Gain Mode Headphone Mute Shutdown Output Stage
Set To
Sel
Sense
DC Volume
Output Stage
Configuration
0
0
0
0
0
Internal Gain
Fixed
BTL
0
0
1
0
0
Internal Gain
Fixed
SE
0
1
0
0
0
Internal Gain
Adjustable
BTL
0
1
1
0
0
Internal Gain
Adjustable
SE
1
0
0
0
0
External Gain
Fixed
BTL
1
0
1
0
0
External Gain
Fixed
SE
1
1
0
0
0
External Gain
Adjustable
BTL
1
1
1
0
0
External Gain
Adjustable
SE
X
X
X
1
0
Muted
X
Muted
X
X
X
X
1
Shutdown
X
X
Note: If system beep is detected on the Beep In pin, the system beep will be passed through
the bridged amplifier regardless of the logic of the Mute and HP sense pins.
■ APPLICATION INFORMATION
• PCB LAYOUT AND SUPPLY REGULATION CONSIDERATIONS FOR DRIVING 3Ω AND
4Ω LOADS
Power dissipated by a load is a function of the voltage swing across the load and the load’s
impedance. As load impedance decreases, load dissipation becomes increasingly dependent
on the interconnect (PCB trace and wire) resistance between the amplifier output pins and the
load’s connections. Residual trace resistance causes a voltage drop, which results in power
dissipated in the trace and not in the load as desired. For example, 0.1Ω trace resistance
reduces the output power dissipated by a 4Ω load from 2.1W to 2.0W. This problem of
decreased load dissipation is exacerbated as load impedance decreases. Therefore, to
maintain the highest load dissipation and widest output voltage swing, PCB traces that
connect the output pins to a load must be as wide as possible. Poor power supply regulation
adversely affects maximum output power. A poorly regulated supply’s output voltage
decreases with increasing load current. Reduced supply voltage causes decreased headroom,
output signal clipping, and reduced output power. Even with tightly regulated sup- plies, trace
resistance creates the same effects as poor supply regulation. Therefore, making the power
supply traces as wide as possible helps maintain full output voltage swing.
• BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 2, the AA4838 output stage consists of two pairs of operational amplifiers,
forming a two-channel (channel A and channel B) stereo amplifier. (Though the following
discusses channel A, it applies equally to channel B.) Figure 2 shows that the first amplifier’s
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DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
negative (-) output serves as the second amplifier’s input. This results in both amplifiers
producing signals identical in magnitude, but 180˚ out of phase. Taking advantage of this
phase difference, a load is placed between −OUTA and +OUTA and driven differentially
(commonly referred to as “bridge mode”). This result in a differential gain of AVD=2*(Rf/Ri)…
(1).
Bridge mode amplifiers are different from single-ended amplifiers that drive loads connected
between a single amplifier’s output and ground. For a given supply voltage, bridge mode has
a distinct advantage over the single-ended configuration: its differential output doubles the
voltage swing across the load. This produces four times the output power when 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 that the output signal is not clipped. To
ensure minimum output signal clipping when choosing an amplifier’s closed-loop gain, refer to
the Audio Power Amplifier Design section. Another advantage of the differential bridge output
is no net DC voltage across the load. This is accomplished by biasing channel A’s and
channel B’s outputs at half-supply. This eliminates the coupling capacitor that single supply,
single- ended amplifiers require. Eliminating an output coupling capacitor in a single-ended
configuration forces a single-supply amplifier’s half-supply bias voltage across the load. This
increases internal IC power dissipation and may permanently damage loads such as
speakers.
• POWER DISSIPATION
Power dissipation is a major concern when designing a successful single-ended or bridged
amplifier. Equation (2) states the maximum power dissipation point for a single- ended
amplifier operating at a given supply voltage and driving a specified output load.
PDMAX=VDD2/2π2RL Single-Ended…(2)
However, a direct consequence of the increased power delivered to the load by a bridge
amplifier is higher internal power dissipation for the same conditions. The AA4838 has two
operational amplifiers per channel. The maximum internal power dissipation per channel
operating in the bridge mode is four times that of a single-ended amplifier. From Equation (3),
assuming a 5V power supply and a 4Ω load, the maximum single channel power dissipation is
1.27W or 2.54W for stereo operation.
PDMAX=4*(VDD) 2/2π2RL Bridge Mode…(3)
The AA4838’s power dissipation is twice that given by Equation (2) or Equation (3) when
operating in the single-ended mode or bridge mode, respectively. Twice the maximum power
dissipation point given by Equation (3) must not exceed the power dissipation given by
Equation (4):
PDMAX'=(TJMAX−TA)/θJA…(4)
The AA4838’s TJMAX=150˚C. In the LQ package soldered to a DAP pad that expands to a
copper area of 5in2 on a PCB, the AA4838’s θJA is 20˚C/W. In the MTE package soldered to
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Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
a DAP pad that expands to a copper area of 2in2 on a PCB, the AA4838MTE’s θJA is
41˚C/W. For the AA4838MT package, θJA=80˚C/W. At any given ambient temperature TA,
use Equation (4) to find the maximum internal power dissipation supported by the IC
packaging. Rearranging Equation (4) and substituting PDMAX for PDMAX' results in Equation
(5). This equation gives the maximum ambient temperature that still allows maximum stereo
power dissipation without violating the AA4838’s maximum junction temperature.
TA=TJMAX–2*PDMAXθJA…(5).
For a typical application with a 5V power supply and a 4Ω load, the maximum ambient
temperature that allows maximum stereo power dissipation without exceeding the maximum
junction temperature is approximately 99˚C for the LQ package and 45˚C for the MTE
package.
TJMAX=PDMAXθJA+TA…(6).
Equation (6) gives the maximum junction temperature TJMAX. If the result violates the
AA4838’s 150˚C TJMAX, reduce the maximum junction temperature by reducing the power
supply voltage or increasing the load resistance. Further allowance should be made for
increased ambient temperatures.
The above examples assume that a device is a surface mount part operating around the
maximum power dissipation point. Since internal power dissipation is a function of output
power, higher ambient temperatures are allowed as output power or duty cycle decreases.
If the result of Equation (2) is greater than that of Equation (3), then decrease the supply
voltage, increase the load impedance, or reduce the ambient temperature. If these measures
are insufficient, a heat sink can be added to reduce θJA. The heat sink can be created using
additional copper area around the package, with connections to the ground pin(s), supply pin
and amplifier output pins. External, solder attached SMT heat sinks such as the Thermally
7106D can also improve power dissipation. When adding a heat sink, the θJA is the sum of
θJC, θCS, and θSA. (θJC is the junction-to-case thermal impedance, θCS is the
case-to-sink thermal impedance, and θSA is the sink-to-ambient thermal impedance.) Refer
to the Typical Performance Characteristics curves for power dissipation information at lower
output power levels.
• POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is critical for low noise performance and
high power supply rejection. Applications that employ a 5V regulator typically use a 10 µF in
parallel with a 0.1 µF filter capacitor to stabilize the regulator’s output, reduce noise on the
supply line, and improve the supply’s transient response. However, their presence does not
eliminate the need for a local 1.0µF tantalum bypass capacitance connected between the
AA4838’s supply pins and ground. Do not substitute a ceramic capacitor for the tantalum.
Doing so may cause oscillation. Keep the length of leads and traces that connect capacitors
between the AA4838’s power supply pin and ground as short as possible. Connecting a 1µF
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DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
capacitor, CB, between the BYPASS pin and ground improves the internal bias voltage’s
stability and the amplifier’s PSRR. The PSRR improvements increase as the BYPASS pin
capacitor value increases. Too large a capacitor, however, increases turn-on time and can
compromise the amplifier’s click and pop performance. The selection of bypass capacitor
values, especially CB, depends on desired PSRR requirements, click and pop performance
(as explained in the following section, Selecting Proper External Components), system cost,
and size constraints.
• SELECTING PROPER EXTERNAL COMPONENTS
Optimizing the AA4838’s performance requires properly selecting external components.
Though the AA4838 operates well when using external components with wide tolerances,
best performance is achieved by optimizing component values. The AA4838 is unity-gain
stable, giving a designer maximum design flexibility. The gain should be set to no more than a
given application requires. This allows the amplifier to achieve minimum THD+N and
maximum signal-to-noise ratio. These parameters are compromised as the closed-loop gain
increases. However, low gain circuits demand input signals with greater voltage swings to
achieve maximum output power. Fortunately, many signal sources such as audio CODECs
have outputs of 1VRMS (2.83VP-P). Please refer to the Audio Power Amplifier Design section
for more information on selecting the proper gain.
• INPUT CAPACITOR VALUE SELECTION
Amplifying the lowest audio frequencies requires a high value input coupling capacitor
(0.33µF in Figure 2), but high value capacitors can be expensive and may compromise space
efficiency in portable designs. In many cases, however, the speakers used in portable
systems, whether internal or external, have little ability to reproduce signals below 150Hz.
Applications using speakers with this limited frequency response reap little improvement by
using a large input capacitor. Besides effecting system cost and size, the input coupling
capacitor has an affect on the AA4838’s click and pop performance. When the supply voltage
is first applied, a transient (pop) is created as the charge on the input capacitor changes from
zero to a quiescent state. The magnitude of the pop is directly proportional to the input
capacitor’s size. Higher value capacitors need more time to reach a quiescent DC voltage
(usually VDD/2) when charged with a fixed current. The amplifier’s output charges the input
capacitor through the feedback resistor, Rf. Thus, pops can be minimized by selecting an
input capacitor value that is no higher than necessary to meet the desired −6dB frequency.
As shown in Figure 2, the input resistor (RIR, RIL = 20k) (and the input capacitor (CIR, CIL=
0.33µF) produce a −6dB high pass filter cutoff frequency that is found using Equation (7).
… (7)
As an example when using a speaker with a low frequency limit of 150Hz, the input coupling
capacitor, using Equation (7), is 0.053µF. The 0.33µF input coupling capacitor shown in
Figure 2 allows the AA4838 to drive a high efficiency, full range speaker whose response
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Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
extends below 30Hz.
• OPTIMIZING CLICK AND POP REDUCTION PERFORMANCE
The AA4838 contains circuitry that minimizes turn-on and shutdown transients or “clicks and
pops”. For this discussion, turn-on refers to either applying the power supply voltage or when
the shutdown mode is deactivated. While the power supply is ramping to its final value, the
AA838’s internal amplifiers are configured as unity-gain buffers. An internal current source
changes the voltage of the BYPASS pin in a controlled, linear manner. Ideally, the input and
outputs track the voltage applied to the BYPASS pin. The gain of the internal amplifiers
remains unity until the voltage on the BYPASS pin reaches 1/2 VDD. As soon as the voltage
on the BYPASS pin is stable, the device becomes fully operational. Although the BYPASS pin
current cannot be modified, changing the size of CB alters the device’s turn-on time and the
magnitude of “clicks and pops”. Increasing the value of CB reduces the magnitude of turn-on
pops. However, this presents a tradeoff: as the size of CB increases, the turn-on time
increases. There is a linear relationship between the size of CB and the turn-on time. Here
are some typical turn-on times for various values of CB:
C
0.01µF
0.1µF
0.22µF
0.47µF
1.0µF
T
2ms
20ms
44ms
94ms
200ms
• DOCKING STATION INTERFACE
Applications such as notebook computers can take advantage of a docking station to connect
to external devices such as monitors or audio/visual equipment that sends or receives line
level signals. The AA4838 has two outputs, Right Dock and Left Dock, which connect to
outputs of the internal input amplifiers that drive the volume control inputs. These input
amplifiers can drive loads of >1kΩ(such as powered speakers) with a rail-to-rail signal. Since
the output signal present on the RIGHT DOCK and LEFT DOCK pins is biased to VDD/2,
coupling capacitors should be connected in series with the load when using these outputs.
Typical values for the output coupling capacitors are 0.33µF to 1.0µF. If polarized coupling
capacitors are used, connect their "+" terminals to the respective output pin, see Figure 2.
Since the DOCK outputs precede the internal volume control, the signal amplitude will be
equal to the input signal’s magnitude and cannot be adjusted. However, the input amplifier’s
closed-loop gain can be adjusted using external resistors. These 20k resistors (RFR, RFL)
are shown in Figure 2 and they set each input amplifier’s gain to -1. Use Equation 7 to
determine the input and feedback resistor values for a desired gain.
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Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
AVR=RFR/RIR and - AVL=RFL/RIL… (8)
Adjusting the input amplifier’s gain sets the minimum gain for that channel. Although the
single ended output of the Bridge Output Amplifiers can be used to drive line level outputs, it
is recommended that the R & L Dock Outputs simpler signal path be used for better
performance.
• BEEP DETECT FUNCTION
Computers and notebooks produce a system “beep“signal that drives a small speaker. The
speaker’s auditory output signifies that the system requires user attention or input. To
accommodate this system alert signal, the AA4838’s beep input pin is a mono input that
accepts the beep signal. Internal level detection circuitry at this input monitors the beep
signal’s magnitude. When a signal level greater than VDD/2 is detected on the BEEP IN pin,
the bridge output amplifiers are enabled. The beep signal is amplified and applied to the load
connected to the output amplifiers. A valid beep signal will be applied to the load even when
MUTE is active. Use the input resistors connected between the BEEP IN pin and the stereo
input pins to accommodate different beep signal amplitudes. These resistors (RBEEP) are
shown as 200kΩ devices in Figure 2. Use higher value resistors to reduce the gain applied
to the beep signal. The resistors must be used to pass the beep signal to the stereo inputs.
The BEEP IN pin is used only to detect the beep signal’s magnitude: it does not pass the
signal to the output amplifiers. The AA4838’s shutdown mode must be deactivated before a
system alert signal is applied to BEEP IN pin.
• MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the AA4838’s shutdown function.
Activate micro-power shutdown by applying VDD to the SHUTDOWN pin. When active, the
AA4838’s micro-power shutdown feature turns off the amplifier’s bias circuitry, reducing the
supply current. The logic threshold is typically VDD/2. The low 0.7 µA typical shutdown
current is achieved by applying a voltage that is as near as VDD as possible to the
SHUTDOWN pin. A voltage that is less than VDD may increase the shutdown current. There
are a few ways to control the micro-power shutdown. These include using a single-pole,
single-throw switch, a microprocessor, or a microcontroller. When using a switch, connect an
external 10kΩ pull-up resistor between the SHUTDOWN pin and VDD. Connect the switch
between the SHUTDOWN pin and ground. Select normal amplifier operation by closing the
switch. Opening the switch connects the SHUTDOWN pin to VDD through the pull-up resistor,
activating micro-power shutdown. The switch and resistor guarantee that the SHUTDOWN
pin will not float. This prevents unwanted state changes. In a system with a microprocessor or
a microcontroller, use a digital output to apply the control voltage to the SHUTDOWN pin.
Driving the SHUTDOWN pin with active circuitry eliminates the need for a pull up resistor.
• MODE FUNCTION
The AA4838’s MODE function has 2 states controlled by the voltage applied to the MODE pin.
Mode 0, selected by applying 0V to the MODE pin, forces the AA4838 to effectively function
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Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
as a "line-out," unity-gain amplifier. Mode 1, which uses the internal DC controlled volume
control is selected by applying VDD to the MODE pin. This mode sets the amplifier’s gain
according to the DC voltage applied to the DC VOL CONTROL pin. Unanticipated gain
behavior can be prevented by connecting the MODE pin to VDD or ground. Note: Do not let
the mode pin float.
• MUTE FUNCTION
The AA4838 mutes the amplifier and DOCK outputs when VDD is applied to the MUTE pin.
Even while muted, the AA4838 will amplify a system alert (beep) signal whose magnitude
satisfies the BEEP DETECT circuitry. Applying 0V to the MUTE pin returns the AA4838 to
normal, unmuted operation. Prevent unanticipated mute behavior by connecting the MUTE
pin to VDD or ground. Do not let the mute pain float.
• HP SENSE FUNCTION (HEAD PHONE IN)
Applying a voltage between 4V and VDD to the AA4838’s HP-IN headphone control pin turns
off the amps that drive the Left out "+" and Right out "+" pins. This action mutes a
ridged-connected load. Quiescent current consumption is reduced when the IC is in this
single-ended mode. Figure 3 shows the implementation of the AA4838’s head- phone control
function. With no headphones connected to the headphone jack, the R1-R2 voltage divider
sets the voltage applied to the HP SENSE pin at approximately 50mV. This 50mV puts the
AA4838 into bridged mode operation. The output coupling capacitor blocks the amplifier’s half
supply DC voltage, protecting the headphones. The HP-IN threshold is set at 4V. While the
AA4838 operates in bridged mode, the DC potential across the load is essentially 0V.
Therefore, even in an ideal situation, the output swing cannot cause a false single-ended
trigger. Connecting headphones to the headphone jack disconnects the head phone jack
contact pin from R2 and allows R1 to pull the HP Sense pin up to VDD through R4. This
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PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
enables the headphone function, turns off both of the "+" output amplifiers, and mutes the
bridged speaker. The remaining single-ended amplifiers then drive the headphones, whose
impedance is in parallel with resistors R2 and R3. These resistors have negligible effect on
the AA4838’s output drive capability since the typical impedance of headphones is 32Ω.
Figure 3 also shows the suggested headphone jack electrical connections. The jack is
designed to mate with a three-wire plug. The plug’s tip and ring should each carry one of the
two stereo output signals, whereas the sleeve should carry the ground return. A headphone
jack with one control pin contact is sufficient to drive the HP-IN pin when connecting
headphones. A microprocessor or a switch can replace the headphone jack contact pin.
When a microprocessor or switch applies a voltage greater than 4V to the HP-IN pin, a
bridge-connected speaker is muted and the single ended output amplifiers 1A and 2A will
drive a pair of headphones.
• GAIN SELECT FUNCTION (Bass Boost)
The AA4838 features selectable gain, using either internal or external feedback resistors.
Either set of feedback resistors set the gain of the output amplifiers. The voltage applied to
the GAIN SELECT pin controls which gain is selected. Applying VDD to the GAIN SELECT
pin selects the external gain mode. Applying 0V to the GAIN SELECT pin selects the
internally set unity gain. At low, frequencies CLFE is a virtual open circuit and at high
frequencies, it’s nearly zero ohm impedance shorts RLFE. The result is increased
bridge-amplifier gain at low frequencies. The combination of RLFE and CLFE form a -6dB
corner frequency at fC=1/(2 π RLFECLFE)…(9) The bridged-amplifier low frequency
differential gain is: AVD= 2(RF+ RLFE) / R i…(10) Using the component values shown in
Figure 1 (RF=20kΩ, RLFE = 20kΩ, and CLFE = 0.068µF), a first-order, -6dB pole is created
at 120Hz. Assuming Ri=20kΩ, the low frequency differential gain is 4. The input (Ci) and
output (CO) capacitor values must be selected for a low frequency response that covers the
range of frequencies affected by the desired bass-boost operation. In some cases a designer
may want to improve the low frequency response of the bridged amplifier or incorporate a
bass boost feature. This bass boost can be useful in systems where speakers are housed in
small enclosures. A resistor, RLFE, and a capacitor, CLFE, in parallel, can be placed in series
with the feedback resistor of the bridged amplifier as seen in Figure 4.
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DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
• DC VOLUME CONTROL
The AA4838 has an internal stereo volume control whose setting is a function of the DC
voltage applied to the DC VOL CONTROL pin. The AA4838 volume control consists of 31
steps that are individually selected by a variable DC voltage level on the volume control pin.
The range of the steps, controlled by the DC voltage, is from 0dB - 78dB. Each gain step
corresponds to a specific input voltage range, as shown in table 2. To minimize the effect of
noise on the volume control pin, which can affect the selected gain level, hysteresis has been
implemented. The amount of hysteresis corresponds to half of the step width, as shown in
Volume Control Characterization Graph (DS200133-40). For highest accuracy, the voltage
shown in the ’recommended voltage’ column of the table is used to select a desired gain. This
recommended voltage is exactly halfway between the two nearest transitions to the next
highest or next lowest gain levels. The gain levels are 1dB/step from 0dB to -6dB, 2dB/step
from -6dB to -36dB, 3dB/step from -36dB to -47dB, 4dB/step from -47db to -51dB, 5dB/step
from -51dB to -66dB, and 12dB to the last step at -78dB.
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DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
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PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
• VOLUME CONTROL TABLE (Table 2)
Gain
(dB)
0
-1
-2
-3
-4
-5
-6
-8
-10
-12
-14
-16
-18
-20
-22
-24
-26
-28
-30
-32
-34
-36
-39
-42
-45
-47
-51
-56
-61
-66
-78
Voltage Range (% of Vdd)
Voltage Range (Vdd = 5)
Low
High
Recommended
Low
77.5
75.0
72.5
70.0
67.5
65.0
62.5
60.0
57.5
55.0
52.5
50.0
47.5
45.0
42.5
40.0
37.5
35.0
32.5
30.0
27.5
25.0
22.5
20.0
17.5
15.0
12.5
10.0
7.5%
5.0%
0.0%
100.00
78.5%
76.25%
73.75%
71.25%
68.75%
66.25%
63.75%
61.25%
58.75%
56.25%
53.75%
51.25%
48.75%
46.25%
43.75%
41.25%
38.75%
36.25%
33.75%
31.25%
28.75%
26.25%
23.75%
21.25%
18.75%
16.25%
13.75%
11.25%
8.75%
6.25%
100.000%
76.875%
74.375%
71.875%
69.375%
66.875%
64.375%
61.875%
59.375%
56.875%
54.375%
51.875%
49.375%
46.875%
44.375%
41.875%
39.375%
36.875%
34.375%
31.875%
29.375%
26.875%
24.375%
21.875%
19.375%
16.875%
14.375%
11.875%
9.375%
6.875%
0.000%
3.875
3.750
3.625
3.500
3.375
3.250
3.125
3.000
2.875
2.750
2.625
2.500
2.375
2.250
2.125
2.000
1.875
1.750
1.625
1.500
1.375
1.250
1.125
1.000
0.875
0.750
0.625
0.500
0.375
0.250
0.000
Voltage Range (Vdd = 3)
High Recommended Low
5.000
3.938
3.813
3.688
3.563
3.438
3.313
3.188
3.063
2.938
2.813
2.688
2.563
2.438
2.313
2.188
2.063
1.938
1.813
1.688
1.563
1.438
1.313
1.188
1.063
0.937
0.812
0.687
0.562
0.437
0.312
5.000
3.844
3.719
3.594
3.469
3.344
3.219
3.094
2.969
2.844
2.719
2.594
2.469
2.344
2.219
2.094
1.969
1.844
1.719
1.594
1.469
1.344
1.219
1.094
0.969
0.844
0.719
0.594
0.469
0.344
0.000
2.325
2.250
2.175
2.100
2.025
1.950
1.875
1.800
1.725
1.650
1.575
1.500
1.425
1.350
1.275
1.200
1.125
1.050
0.975
0.900
0.825
0.750
0.675
0.600
0.525
0.450
0.375
0.300
0.225
0.150
0.000
High Recommended
3.000
2.363
2.288
2.213
2.138
2.063
1.988
1.913
1.838
1.763
1.688
1.613
1.538
1.463
1.388
1.313
1.238
1.163
1.088
1.013
0.937
0.862
0.787
0.712
0.637
0.562
0.487
0.412
0.337
0.262
0.187
3.000
2.306
2.231
2.156
2.081
2.006
1.931
1.856
1.781
1.706
1.631
1.556
1.481
1.406
1.331
1.256
1.181
1.106
1.031
0.956
0.881
0.806
0.731
0.656
0.581
0.506
0.431
0.356
0.281
0.206
0.000
• AUDIO POWER AMPLIFIER DESIGN
Audio Amplifier Design: Driving 1W into an 8ΩLoad
The following are the desired operational parameters:
Power Output: 1 WRMS,
Load Impedance: 8Ω, Input Level:1 VRMS,
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Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
Input Impedance: 20 kΩ,
Bandwidth: 100 Hz−20 kHz ± 0.25 dB
The design begins by specifying the minimum supply voltage necessary to obtain the
specified output power. One way to find the minimum supply voltage is to use the Output
Power vs. Supply Voltage curve in the Typical Performance Characteristics section. Another
way, using Equation (10), is to calculate the peak output voltage necessary to achieve the
desired output power for a given load impedance. To account for the amplifier’s dropout
voltage, two additional voltages, based on the Dropout Voltage vs. Supply Voltage in the
Typical Performance Characteristics curves, must be added to the result obtained by
Equation (10). The result is Equation (11).
… (11),
VDD≧ (VOUTPEAK+ (VODTOP+VODBOT))… (12)
The Output Power vs. Supply Voltage graph for an 8Ω load indicates a minimum supply
voltage of 4.6V. This is easily met by the commonly used 5V supply voltage. The additional
voltage creates the benefit of headroom, allowing the AA4838 to produce peak output power
in excess of 1W without clipping or other audible distortion. The choice of supply voltage must
also not create a situation that violates of maximum power dissipation as explained above in
the Power Dissipation section. After satisfying the AA4838’s power dissipation requirements,
the minimum differential gain needed to achieve 1W dissipation in an 8Ωload is found using
Equation (12).
… (13)
Thus, a minimum overall gain of 2.83 allow the AA4838’s to reach full output swing and
maintain low noise and THD+N performance. The last step in this design example is setting
the amplifier’s −6dB frequency bandwidth. To achieve the desired ±0.25dB pass band
magnitude variation limit, the low frequency response must extend to at least one-fifth the
lower bandwidth limit and the high frequency response must extend to at least five times the
upper bandwidth limit. The gain variation for both response limits is 0.17dB, well within the
±0.25dB desired limit. The results are an fL=100Hz/5=20Hz…(14) and an fH=20kHz x
5=100kHz…(15) As mentioned in the Selecting Proper External Components section, Ri
(Right & Left) and Ci (Right & Left) create a high pass filter that sets the amplifier’s lower
band pass frequency limit. Find the input coupling capacitor’s value using Equation (14).
Ci≧1/(2πRifL)…(16)
The result is
1/(2π*20kΩ*20Hz)=0.397µF…(17)
Use a 0.39µF capacitor, the closest standard value.
The product of the desired high frequency cutoff (100 kHz in this example) and the differential
gain AVD, determines the upper pass band response limit. With AVD= 3 and fH =100 kHz,
the closed-loop gain bandwidth product (GBWP) is 300 kHz. This is less than the AA4838’s
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Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
3.5MHz GBWP. With this margin, the amplifier can be used in designs that require more
differential gain while avoiding performance, restricting bandwidth limitations.
• RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT
The following figures show the recommended PC board layouts that are optimized for the
different package options of the AA4838 and associated external components. This circuit is
designed for use with an external 5V supply and 4Ω speakers. This circuit board is easy to
use. Apply 5V and ground to the board’s VDD and GND pads, respectively. Connect 4Ω
speakers between the board’s −OUTA and +OUTA and OUTB and +OUTB pads.
■ ORDERING INFORMATION
ORDER NO.
PACKAGE
PACKING
ONE REEL Q’TY
AA4838A
TSSOP 28L
Tape & Reel
2,500ea
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MARK CHART
AA4838
XXXX
A
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Agamem Microelectronics Inc.
PRELIMINARY
AA4838
AUDIO POWER AMPLIFIER
■ PACKAGE DIMENSIONS
TSSOP 28L
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