LM4890

TIGER ELECTRONICO.,LTD
LM4890
1 WATT AUDIO POWER AMPLIFIER
General Description
The LM4890 is an audio power amplifier primarily designed for demanding applications in mobile
phones and ther portable communication device applications. It is capable of delivering 1 watt of
continuous average power to an 8Ω BTL load with less than 1% distortion (THD+N) from a 5VDC
power supply.
Boomer audio power amplifiers were designed specifically to provide high quality output power
with a minimal amount of external components. The LM4890 does not require output coupling
capacitors or bootstrap capacitors, and therefore is ideally suited for mobile phone and other low
voltage applications where minimal power consumption is a primary requirement.
The LM4890 features a low-power consumption shutdown mode, which is achieved by driving the
shutdown pin with logic low. Additionally, the LM4890 features an internal thermal shutdown
protection mechanism. The LM4890 contains advanced pop & click circuitry which eliminates noises which would otherwise
occur during turn-on and turn-off transitions.The LM4890 is unity-gain stable and can be
configured by external gain-setting resistors.
Key Specifications
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PSRR at 217Hz, VDD = 5V (Fig. 1)
Power Output at 5.0V & 1% THD
Power Output at 3.3V & 1% THD
Shutdown Current 0.1Μa
62dB(typ.)
1W(typ.)
400mW(typ.)
(typ.)
Features
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Available in space-saving packages: micro SMD, MSOP, SOIC, and LLP
Ultra low current shutdown mode
BTL output can drive capacitive loads
Improved pop & click circuitry eliminates noises during turn-on and turn-off transitions
2.2 - 5.5V operation
No output coupling capacitors, snubber networks or bootstrap capacitors required
Thermal shutdown protection
Unity-gain stable
External gain configuration capability
Applications
LM4890
◆ Mobile Phones
◆ PDAs
◆ Portable electronic devices
Absolute Maximum Ratings (Note 2)
Supply Voltage (Note 11)
Storage Temperature
Input Voltage
Power Dissipation (Note 3)
ESD Susceptibility (Note 4)
Junction Temperature
Thermal Resistance
θJC (SOP)
θJA (SOP)
6.0V
−65°C to +150°C
−0.3V to VDD +0.3V
Internally Limited
2000V
150°C
35°C/W
150°C/W
LM4890
θJA (8 Bump micro SMD, Note 12) 220°C/W
θJA (9 Bump micro SMD, Note 12) 180°C/W
θJC (MSOP)
56°C/W
θJA (MSOP)
190°C/W
θJA (LLP)
220°C/W
Soldering Information
See AN-1112 "microSMD Wafers Level Chip Scale Package."
See AN-1187 "Leadless Leadframe Package (LLP)."
Operating Ratings
Temperature Range
TMIN ≤TA ≤TMAX
Supply Voltage
-40°C ≤TA ≤85°C
2.2V ≤VDD ≤5.5V
Electrical Characteristics VDD = 5V (Notes 1, 2, 8)
The following specifications apply for the circuit shown in Figure 1 unless otherwise specified.
Limits apply for TA = 25°C
Symbol
IDD
Parameter
Quiescent Power
Supply Current
Conditions
LM4890
Units
(Limits)
Typical
Limit
(Note 6)
(Notes 7, 9)
VIN = 0V, Io =
0A, No Load
4
8
mA (max)
VIN = 0V, Io =
0A, 8Ω Load
5
10
mA (max)
VSHUTDOWN = 0V
0.1
2.0
μA (max)
ISD
Shutdown Current
VSDIH
Shutdown Voltage
Input High
1.2
V (min)
VSDIL
Shutdown Voltage
Input Low
0.4
V (max)
VOS
Output Ofsett Voltage
7
50
mV (max)
ROUT-GND
Resistor Output to
GND (Note 10)
8.5
9.7
k　(max)

7.0
k　(min)

1.0
0.8
W
Po
Output Power ( 8 Ω )
THD = 2%(max);
f = 1 kHz
TWU
Wake-up time
170
220
ms (max)
TSD
Thermal Shutdown
Temperature
170
150
°C (min)
190
°C (max)
THD+N
Total Harmonic
Distortion+Noise
Po = 0.4 Wrms; f
= 1kHz
0.1
PSRR
Power Supply
Vripple = 200mV
62 (f =
%
55
dB (min)
LM4890
TSDT
Rejection Ratio
(Note 14)
sine p-p
Input
Terminated with
10 ohms to
ground
217Hz)
66 (f =
1kHz)
Shut Down Time
8 Ω load
1.0
ms (max)
Electrical Characteristics VDD = 3V (Notes 1, 2, 8)
The following specifications apply for the circuit shown in Figure 1 unless otherwise specified.
Limits apply for TA = 25°C.
Symbol
IDD
Parameter
Quiescent Power
Supply Current
Conditions
LM4890
Units
(Limits)
Typical
Limit
(Note 6)
(Notes 7,9)
VIN = 0V,Io= 0A,
No Load
3.5
7
mA (max)
VIN = 0V,Io= 0A,
8 Ω Load
4.5
9
mA (max)
VSHUTDOWN = 0V
0.1
2.0
μA (max)
ISD
Shutdown Current
VSDIH
Shutdown Voltage
Input High
1.2
V (min)
VSDIL
Shutdown Voltage
Input Low
0.4
V (max)
VOS
Output Ofsett Voltage
7
50
mV (max)
ROUT-GND
Resistor Output to
GND (Note 10)
8.5
9.7
k　(max)

7.0
k　(min)

120
180
W
Po
Output Power ( 8 Ω )
THD = 1%(max);
f = 1 kHz
TWU
Wake-up time
0.13
0.28
ms (max)
TSD
Thermal Shutdown
Temperature
170
150
°C (min)
190
°C (max)
THD+N
Total Harmonic
Distortion+Noise
Po = 0.15 Wrms;
f = 1kHz
0.1
PSRR
Power Supply
Rejection Ratio
(Note 14)
Vripple = 200mV
sine p-p
Input
Terminated with
10 ohms to
ground
56 (f =
217Hz)
62 (f =
1kHz)
%
4.5
dB (min)
LM4890
Electrical Characteristics VDD = 2.6V (Notes 1, 2, 8)
The following specifications apply for the circuit shown in Figure 1 unless otherwise specified.
Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LM4890
Typical
Limit
(Note 6)
(Notes 7,9)
Units
(Limits)
IDD
Quiescent Power
Supply Current
VIN = 0V,Io= 0A,
No Load
2.6
mA (max)
ISD
Shutdown Current
VSHUTDOWN = 0V
0.1
μA (max)
Po
Output Power ( 8 Ω )
Output Power ( 4 Ω)
THD = 1%(max);
f = 1 kHz
0.2
0.22
W
W
THD+N
Total Harmonic
Distortion+Noise
Po = 0.1 Wrms; f
= 1kHz
0.08
%
PSRR
Power Supply
Rejection Ratio
(Note 14)
Vripple = 200mV
sine p-p
Input
Terminated with
10 ohms to
ground
44 (f =
217Hz)
44 (f =
1kHz)
dB
Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified.
Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating
Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits.
Electrical Characteristics state DC and AC electrical specifications under particular test conditions which
guarantee specific performance limits. This assumes that the device is within the Operating Ratings.
Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good
indication of device performance.
Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX,
JA, and the ambient temperature TA. The maximumallowable power dissipation is PDMAX = (TJMAX–TA)/　JA
or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4890, see power
deratingcurves for additional information.
Note 4: Human body model, 100 pF discharged through a 1.5 k　resistor.

Note 5: Machine Model, 220 pF–240 pF discharged through all pins.
Note 6: Typicals are measured at 25°C and represent the parametric norm.
Note 7: Limits are guaranteed to ASIC’s AOQL (Average Outgoing Quality Level).
Note 8: For micro SMD only, shutdown current is measured in a Normal Room Environment. Exposure to direct
sunlight will increase ISD by a maximum of
μA.
Note 9: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Note 10: ROUT is measured from each of the output pins to ground. This value represents the parallel
LM4890
combination of the 10k ohm output resistors and the two 20kohm resistors.
Note 11: If the product is in shutdown mode and VDD exceeds 6V (to a max of 8V VDD), then most of the excess
current will flow through the ESD protection circuits.
If the source impedance limits the current to a max of 10 ma, then the part will be protected. If the part is enabled
when VDD is greater than 5.5V and less than 6.5V, no damage will occur, although operational life will be
reduced. Operation above 6.5V with no current limit will result in permanent damage.
Note 12: All bumps have the same thermal resistance and contribute equally when used to lower thermal
resistance. All bumps must be connected to achieve specified thermal resistance.
Note 13: Maximum power dissipation (PDMAX) in the device occurs at an output power level significantly below
full output power. PDMAX can be calculated using Equation 1 shown in the Application section. It may also be
obtained from the power dissipation graphs.
Note 14: PSRR is a function of system gain. Specifications apply to the circuit in Figure 1 where AV = 2. Higher
system gains will reduce PSRR value by the amount of gain increase. A system gain of 10 represents a gain
increase of 14dB. PSRR will be reduced by 14dB and applies to all operating voltages.
External Components Description (Figure 1)
Components
Functional Description
1.
RIN
Inverting input resistance which sets the closed-loop gain in conjunction
with Rf. This resistor also forms a
 INCIN).
high pass filter with CIN at fC= 1/(2　R
2.
CIN
Input coupling capacitor which blocks the DC voltage at the amplifier’s
 INCIN).
input terminals. Also creates a highpass filter with RIN at fc = 1/(2　R
Refer to the section, Proper Selection of External Components, for an
explanation of how to determine the value of CIN.
3.
Rf
Feedback resistance which sets the closed-loop gain in conjunction with
RIN.
4.
CS
Supply bypass capacitor which provides power supply filtering. Refer to the
section, Power Supply Bypassing, for information concerning proper
placement and selection of the supply bypass capacitor, CBYPASS.
5.
CBYPASS
Bypass pin capacitor which provides half-supply filtering. Refer to the
section, Proper Selection of External Components, for information
concerning proper placement and selection of CBYPASS.
Application Information
BRIDGED CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4890 has two operational amplifiers internally, allowing for a few
different amplifier configurations. 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 Rf to RIN while the second amplifier’s gain is fixed
by the two internal 20k　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
LM4890
out of phase by 180°. Consequently, the differential gain for the IC is
AVD= 2 *(Rf/RIN)
By driving the load differentially through outputs Vo1 and Vo2, an 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.
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, please refer to the Audio Power Amplifier Design section.
A bridge configuration, such as the one used in the LM4890, also creates a second advantage
over single-ended amplifiers. Since the differential outputs, Vo1 and Vo2, are biased at halfsupply, 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 possible 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. Since the LM4890 has two
operational amplifiers in one package, the maximum internal power dissipation is 4 times that of a
single-ended amplifier. The maximum power dissipation for a given application can be derived
from the power dissipation graphs or from Equation 1.
PDMAX = 4*(VDD) 2/ (2　2RL) (1)
It is critical that the maximum junction temperature TJMAX of 150°C is not exceeded. TJMAX can
be determined from the power derating curves by using PDMAX and the PC board foil area. By
adding additional copper foil, the thermal resistance of the application can be reduced, resulting
in higher PDMAX. Additional copper foil can be added to any of the leads connected to the
LM4890. Refer to the APPLICATION INFORMATION on the LM4890 reference design board for
an example of good heat sinking. If TJMAX still exceeds 150°C, then additional changes must be
made. These changes can include reduced supply voltage, higher load impedance, or reduced
ambient temperature. Internal power dissipation is a function of output power. Refer to the
Typical Performance Characteristics curves for power dissipation information for different
output powers and output loading.
POWER SUPPLY BYPASSING
As with any 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. Typical applications employ a 5V regulator with 10 μF
LM4890
tantalum or electrolytic capacitor and a ceramic bypass capacitor which aid in supply stability.
This does not eliminate the need for bypassing the supply nodes of the LM4890. The selection of
a bypass capacitor, especially CBYPASS, is dependent upon PSRR 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 LM4890 contains a shutdown pin to
externally turn off the amplifier’s bias circuitry. This shutdown feature turns the amplifier off when
a logic low is placed on the shutdown pin.
By switching the shutdown pin to ground, the LM4890 supply current draw will be minimized in
idle mode. While the device will be disabled with shutdown pin voltages less than 0.5VDC, the
idle current may be greater than the typical value of 0.1μA. (Idle current is measured with the
shutdown pin grounded).
In many applications, a microcontroller or microprocessor output is used to control the shutdown
circuitry to provide a quick, smooth transition into shutdown. Another solution is to use a singlepole, single-throw switch in conjunction with an external pull-up resistor. When the switch is
closed, the shutdown pin is connected to ground and disables the amplifier.
If the switch is open, then the external pull-up resistor will enable the LM4890. This scheme
uarantees that the shutdown pin will not float thus preventing unwanted state changes.
SHUTDOWN OUTPUT IMPEDANCE
For Rf = 20k ohms:
ZOUT1 (between Out1 and GND) = 10k||50k||Rf = 6k　ZOUT2 (between Out2 and GND) = 10k||(40k+(10k||Rf)) = 8.3k　ZOUT1-2 (between Out1 and Out2) = 40k||(10k+(10k||Rf)) = 11.7k　The -3dB roll off for these measurements is 600kHz
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications using integrated power amplifiers is
critical to optimize device and system performance. While the LM4890 is tolerant of external
component combinations, consideration to component values must be used to maximize overall
system quality.
The LM4890 is unity-gain stable which gives the designer maximum system flexibility. The
LM4890 should be used in low gain configurations to minimize THD+N values, and maximize the
signal to noise ratio. Low gain configurations require large input signals to obtain a given output
power. Input signals equal to or greater than 1Vrms are available from sources such as audio
codecs. Please refer to the section, Audio Power Amplifier Design, for a more complete
explanation of proper gain selection.
Besides gain, one of the major considerations is the closedloop bandwidth of the amplifier. To a
large extent, the bandwidth is dictated by the choice of external components shown in Figure 1.
LM4890
The input coupling capacitor, CIN, forms a first order high pass filter which limits low frequency
response. This value should be chosen based on needed frequency response for a few distinct
reasons.
Selection Of Input Capacitor Size
Large input capacitors are both expensive and space hungry for portable designs. Clearly, a
certain sized capacitor is needed to couple in low frequencies without severe attenuation. But in
many cases the speakers used in portable systems, whether internal or external, have little ability
to reproduce signals below 100Hz to 150Hz. Thus, using a large input capacitor may not increase
actual system performance.
In addition to system cost and size, click and pop performance is effected by the size of the input
coupling capacitor, CIN. A larger input coupling capacitor requires more charge to reach its
quiescent DC voltage (nominally 1/2 VDD). This charge comes from the output via the feedback
and is apt to create pops upon device enable. Thus, by minimizing the capacitor size based on
necessary low frequency response, turn-on pops can be minimized.
Besides minimizing the input capacitor size, careful consideration should be paid to the bypass
capacitor value. Bypass capacitor, CBYPASS, is the most critical component to minimize turn-on
pops since it determines how fast the LM4890 turns on. The slower the LM4890’s outputs ramp to
their quiescent DC voltage (nominally 1/2VDD), the smaller the turn-on pop. Choosing CBYPASS
equal to 1.0μF along with a small value of CIN, (in the range of 0.1μF to 0.39μF), should produce
a virtually clickless and popless shutdown function. While the device will function properly, (no
oscillations or motorboating), with CBYPASS equal to 0.1μF, the device will be much more
susceptible to turn-on clicks and pops. Thus, a value of CBYPASS equal to 1.0μF is
recommended in all but the most cost sensitive designs.
AUDIO POWER AMPLIFIER DESIGN
A 1W/8Ω AUDIO AMPLIFIER
Given:
Power Output
1 Wrms
Load Impedance
8Ω
Input Level
1 Vrms
Input Impedance
20 kΩ
Bandwidth
100 Hz–20 kHz ± 0.25 dB
A designer must first determine the minimum supply rail to obtain the specified output power. By
extrapolating from the Output Power vs Supply Voltage graphs in the Typical Performance
Characteristics section, the supply rail can be easily found. A second way to determine the
minimum supply rail is to calculate the required Vopeak using Equation 2 and add the output
voltage. Using this method, the minimum supply voltage would be (Vopeak + (VODTOP + VODBOT)),
where VODBOT and VODTOP are extrapolated from the Dropout Voltage vs Supply Voltage curve in
the Typical Performance Characteristics section.
VOPEAK=√(2RLPO)
LM4890
5V is a standard voltage which in most applications is chosen for the supply rail. Extra supply
voltage creates headroom that allows the LM4890 to reproduce peaks in excess of 1W without
producing audible distortion. At this time, the designer must make sure that the power supply
choice along with the output impedance does not violate the conditions explained in the Power
Dissipation section. Once the power dissipation equations have been addressed, the required
differential gain can be determined from Equation 3.
(3)
AVD≥√(PORL)∕(VIN)=Vorms /Vinrms
Rf/RIN = AVD/2
From Equation 3, the minimum AVD is 2.83; use AVD = 3.
Since the desired input impedance is 20 kΩ, and with an AVD gain of 3, a ratio of 1.5:1 of Rf to RIN
results in an allocation of RIN = 20 kΩ and Rf = 30 kΩ. The final design step is to address the
bandwidth requirements which must be stated as a pair of −3 dB frequency points. Five times
away from a −3 dB point is 0.17 dB down from passband response which is better than the
required ±0.25 dB specified.
fL = 100Hz/5 = 20Hz
fH = 20kHz * 5 = 100kHz
As stated in the External Components section, RIN in conjunction with CIN create a highpass
filter.
CIN ≥ 1/(2π*20 kΩ*20Hz) = 0.397μF; use 0.39μF
The high frequency pole is determined by the product of the desired frequency pole, fH, and the
differential gain, AVD. With a AVD = 3 and fH = 100kHz, the resulting GBWP = 300kHz which is
much smaller than the LM4890 GBWP of 2.5MHz. This calculation shows that if a designer has a
need to design an amplifier with a higher differential gain, the LM4890 can still be used without
running into bandwidth limitations. The
LM4890 is unity-gain stable and requires no external components besides gain-setting resistors,
an input coupling capacitor, and proper supply bypassing in the typical application. However, if a
closed-loop differential gain of greater than 10 is required, a feedback capacitor (C4) may be
needed as shown in Figure 2 to bandwidth limit the amplifier. This feedback capacitor creates a
low pass filter that eliminates possible high frequency oscillations. Care should be taken when
calculating the -3dB frequency in that an incorrect combination of R3 and C4 will cause rolloff
before 20kHz. A typical combination of feedback resistor and capacitor that will not produce audio
band high frequency rolloff is R3 = 20kΩ and C4 = 25pf. These components result in a -3dB point
of approximately 320 kHz.
LM4890
Application Information (Continued)
DIFFERENTIAL AMPLIFIER CONFIGURATION FOR LM4890
LM4890
FIGURE 3
REFERENCE DESIGN BOARD and LAYOUT - micro SMD
LM4890
FIGURE 4.
LM4890
Physical Dimensions inches (millimeters)
unless otherwise noted
Note: Unless otherwise specified.
1. Epoxy coating.
2. 63Sn/37Pb eutectic bump.
3. Recommend non-solder mask defined landing pad.
4. Pin 1 is established by lower left corner with respect to text orientation pins are numbered
counterclockwise.
5. Reference JEDEC registration MO-211, variation BC.
8-Bump micro SMD
Order Number LM4890IBP, LM4890IBPX
NS Package Number BPA08DDB
X1 = 1.361±0.03 X2 = 1.361±0.03 X3 = 0.850±0.10
LM4890
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
9-Bump micro SMD
Order Number LM4890IBL, LM4890IBLX
NS Package Number BLA09AAB
X1 = 1.514±0.03 X2 = 1.514±0.03 X3 = 0.945±0.10
LM4890
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
MSOP
Order Number LM4890MM
NS Package Number MUA08A
LM4890
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
SO
Order Number LM4890M
NS Package Number M08A
LM4890
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
LM4890
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
This integrated circuit can be damaged by ESD.
The TIGER ELELTRONIC CO., recommends
that all integrated circuits be handled with
appropriate precautions. Failure to observe
proper handling and installation procedures can
cause damage.
ESD damage can range from subtle
performance degradation to complete device
failure. Precision integrated circuits may be
more susceptible to damage because very small
parametric changes could cause the device not
to meet its published specifications.
LM4890