1
2
3
4
5
6
78 9 10 11 12 13 14 15
16
17
18
19
20
21
22232425262728
SW-OUT
Bypass
Shutdown 2
VDD
NC
Shutdown 1
GND
FB
NC
NC
SW
GND
NC
NC
BW2
BW1
Band-SW
VIN
CCHG
NC
NC
GND
Vout+
Vamp
NC
GND
Vout-
NC
LM4961, LM4961LQBD
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SNAS242K –AUGUST 2004–REVISED MAY 2013
LM4961 Ceramic Speaker Driver
Check for Samples: LM4961,LM4961LQBD
1FEATURES DESCRIPTION
The LM4961 is an audio power amplifier primarily
2• Click and Pop Circuitry Eliminates Noise designed for driving Ceramic Speaker for applications
During Turn-On and Turn-Off Transitions in Cell Phone and PDAs. It integrates a boost
• Low Current Shutdown Mode converter, with variable output voltage, with an audio
• Low Quiescent Current power amplifier. It is capable of driving 15Vp-p in BTL
mode to 2uF+ 30 ohms load, continuous average
• Mono 15Vp-p BTL Output, RL= 2μF+30Ω,f= power, with less than 1% distortion (THD+N) from a
1kHz 3.2VDC power supply.
• Thermal Shutdown Protection Boomer audio power amplifiers were designed
• Unity-Gain Stable specifically to provide high quality output power with a
• External Gain Configuration Capability minimal number of external components. The
LM4961 does not require bootstrap capacitors, or
• Including Band Exchange SW snubber circuits therefore it is ideally suited for
• Including Leakage Cut SW portable applications requiring high voltage output to
drive capacitive loads like Ceramic Speakers. The
APPLICATIONS LM4961 features a low-power consumption shutdown
mode. Additionally, the LM4961 features an internal
• Cellphone thermal shutdown protection mechanism.
• PDA The LM4961 contains advanced pop & click circuitry
KEY SPECIFICATIONS that eliminates noises which would otherwise occur
during turn-on and turn-off transitions.
• Quiescent Power Supply Current: 7mA (typ) The LM4961 is unity-gain stable and can be
• Voltage Swing in BTL at 1% THD: 15Vp-p (typ) configured by external gain-setting resistors.
• Shutdown current: 0.1μA (typ)
Connection Diagram
Figure 1. LM4961LQ (5x5) (Top View)
See Package Number NJB0028A
1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 2004–2013, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Shutdown 1
GND
12
6
GND
7
114 SW
VDD
L1
10 PH
FB 8
470 pF
13k
SW-Out 1
68k
Shutdown 1
Band-SW
19
Band-SW
Shutdown 2
3
Shutdown 2
4.7 PF
SW GND 28
4.7 PF
VI26
4.7 PF
GND 24
1.0 PF
Bypass
2
15
VO2 27
15
VO1 23 2 PF
Ceramic
20k
Cchg
17
VIN
18
0.1 PF
Audio In
20k
200k
82 pF
BW2BW1 2120
VDD
VI = VFB(1 + R2/(R3 + 170))**
Load
CO
R2
D1
CF
R3
CS1
CBYPASS
CiRi
CF1
RF2
RF1
CS2
*Rc
1k
LM4961, LM4961LQBD
SNAS242K –AUGUST 2004–REVISED MAY 2013
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Typical Application
* RCis needed for over/under voltage protection. If inputs are less than VDD +0.3V and greater than –0.3V, and if
inputs are disabled when in shutdown mode, then RCcan be shorted.
** VFB = 1.23V
Figure 2. Typical Audio Amplifier Application Circuit
Shutdown 1 Shutdown 2 Band-SW
Receiver Mode (BW2) — high low
Ringer Mode (BW1) high high high
Shutdown low low low
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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Absolute Maximum Ratings(1)(2)(3)
Supply Voltage (Vdd) 6.0V
Amplifier Supply Voltage (V1) 9.5V
Storage Temperature −65°C to +150°C
Input Voltage −0.3V to VDD + 0.3V
Power Dissipation(4) Internally limited
ESD Susceptibility(5) 2000V
ESD Susceptibility(6) 200V
Junction Temperature 150°C
Thermal Resistance
θJA (WQFN) 66°C/W
(1) All voltages are measured with respect to the GND pin, unless otherwise specified.
(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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
(3) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
(4) The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX,θJA, and the ambient temperature,
TA. The maximum allowable power dissipation is PDMAX = (TJMAX −TA) / θJA or the given in Absolute Maximum Ratings, whichever is
lower. For the LM4961 typical application (shown in Figure 2) with VDD = 4.2V, RL= 2μF+30Ωmono BTL operation the maximum power
dissipation is 232mW. θJA = 66°C/W.
(5) Human body model, 100pF discharged through a 1.5kΩresistor.
(6) Machine Model, 220pF–240pF discharged through all pins.
Operating Ratings
Temperature Range
TMIN ≤TA≤TMAX −40°C ≤TA≤+85°C
Supply Voltage (VDD) 3.0V < VDD < 5.0V
Amplifier Supply Voltage (V1) 2.7V < V1< 9.0V
Electrical Characteristics VDD = 4.2V
The following specifications apply for VDD = 4.2V, AV-BTL = 26dB, RL= 2µF+30Ω, Cb = 1.0μF, Band-SW = VDD unless
otherwise specified. Limits apply for TA= 25°C.
Symbol Parameter Conditions LM4961 Units
(Limits)
Typical(1) Limit(2)(3)
IDD Quiescent Power Supply Current VIN = 0V, No Load 7 14 mA (max)
Band-SW = VDD
Iddrcv Iq in receiver mode VIN = 0V, No Load 2 4 mA (max)
Band-SW = GND
ISD Shutdown Current VSHUTDOWN1 = VSHUTDOWN2 = GND 0.1 2.0 µA (max)
Band-SW = GND (Note 9)
VLH Logic High Threshold Voltage For Shutdown 1, Shutdown 2, and 1.5 V (min)
Band-SW
VLL Logic Low Threshold Voltage For Shutdown 1, Shutdown 2, and 0.4 V (max)
Band-SW
RPULLDOWN Pulldown Resistor For Shutdown 2 and Band-SW 70k 50k Ω(min)
TSD Thermal Shutdown Temperature 125 °C (min)
THD = 1%, f = 1kHz
Vout Output Voltage Swing 15 14 Vp-p (min)
RL= 2μF+30ΩMono BTL
THD+N Total Harmomic Distortion + Noise Vout = 14Vp-p, f = 1kHz 0.05 1.0 % (max)
εOS Output Noise A-Weighted Filter, VIN = 0V (Note 10) 115 µV
(1) Typicals are measured at 25°C and represent the parametric norm.
(2) Limits are specified to AOQL (Average Outgoing Quality Level).
(3) Datasheet min/max specification limits are specified by design, test, or statistical analysis.
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Electrical Characteristics VDD = 4.2V (continued)
The following specifications apply for VDD = 4.2V, AV-BTL = 26dB, RL= 2µF+30Ω, Cb = 1.0μF, Band-SW = VDD unless
otherwise specified. Limits apply for TA= 25°C.
Symbol Parameter Conditions LM4961 Units
(Limits)
Typical(1) Limit(2)(3)
PSRR Power Supply Rejection Ratio VRIPPLE = 200mVp-p, f = 100Hz 80 65 dB (min)
Ron-sw-out On Resistance on SW-Out Band SW “High” Isink = 100µA 170 220 Ω(max)
(Between pin 1 and pin 28)
TWUA Amplifier Wake-up Time CB= 1μF 25 35 ms (max)
Electrical Characteristics VDD = 3.2V
The following specifications apply for VDD = 3.2V, AV-BTL = 26dB, RL= 2µF+30Ω, Cb = 1.0μF, Band-SW = VDD unless
otherwise specified. Limits apply for TA= 25°C.
Symbol Parameter Conditions LM4961 Units
(Limits)
Typical(1) Limit(2)(3)
IDD Quiescent Power Supply Current VIN = 0V, No Load 9 15 mA (max)
Band-SW = VDD
Iddrcv Iq in receiver mode VIN = 0V, No Load 2 4 mA (max)
Band-SW = GND
ISD Shutdown Current VSHUTDOWN1 = VSHUTDOWN2 = GND 0.1 2.0 µA (max)
Band-SW = GND (Note 9)
VLH Logic High Threshold Voltage For Shutdown 1, Shutdown 2, and 1.5 V (min)
Band-SW
VLL Logic Low Threshold Voltage For Shutdown 1, Shutdown 2, and 0.4 V (max)
Band-SW
RPULLDOWN Pulldown Resistor For Shutdown 2 and Band-SW 70k 50k Ω(min)
TSD Thermal Shutdown Temperature 125 °C (min)
THD = 1%, f = 1kHz
Vout Output Voltage Swing 15 14 Vp-p (min)
RL= 2μF+30ΩMono BTL
THD+N Total Harmomic Distortion + Noise Vout = 14Vp-p, f = 1kHz 0.1 1.0 % (max)
εOS Output Noise A-Weighted Filter, VIN = 0V (Note 10) 125 µV
PSRR Power Supply Rejection Ratio VRIPPLE = 200mVp-p, f = 100Hz 80 65 dB (min)
Ron-sw-out On Resistance on SW-Out Band SW “High” Isink = 100µA 170 220 Ω(max)
(Between pin 1 and pin 28)
(1) Typicals are measured at 25°C and represent the parametric norm.
(2) Limits are specified to AOQL (Average Outgoing Quality Level).
(3) Datasheet min/max specification limits are specified by design, test, or statistical analysis.
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1k 10k
FREQUENCY (Hz)
-100
-95
-90
-85
-80
-75
-70
-65
-60
-55
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
PSRR (dB)
100 2k200 5k500
1k 10k
FREQUENCY (Hz)
-100
-95
-90
-85
-80
-75
-70
-65
-60
-55
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
PSRR (dB)
100 2k200 5k500
010 15 25
OUTPUT VOLTAGE (Vp-p)
0.01
0.1
10
THD+N (%)
1
520
100 Hz
1 kHz
10 kHz
010 15 25
OUTPUT VOLTAGE (Vp-p)
0.01
0.1
10
THD+N (%)
1
520
100 Hz
10 kHz
1 kHz
100 1k 10k
FREQUENCY (Hz)
0.01
0.02
0.05
0.1
0.2
0.5
1
2
5
10
THD+N (%)
200 2k
500 5k
100 500 2k 10k
FREQUENCY (Hz)
0.01
0.1
1
10
THD+N (%)
LM4961, LM4961LQBD
www.ti.com
SNAS242K –AUGUST 2004–REVISED MAY 2013
Typical Performance Characteristics
THD+N vs Frequency THD+N vs Frequency
VDD = 4.2V, VO= 14VP-P, RL= 2μF+30ΩVDD = 3.2V, VO= 14VP-P, RL= 2μF+30Ω
Figure 3. Figure 4.
THD+N vs Output Voltage THD+N vs Output Voltage
VDD = 4.2V, RL= 2μF + 30ΩVDD = 3.2V, RL= 2μF + 30Ω
Figure 5. Figure 6.
PSRR vs Frequency PSRR vs Frequency
VDD = 4.2V, RL= 8Ω, VRIPPLE = 200mVP-P VDD = 3.2V, RL= 8Ω, VRIPPLE = 20mVP-P
Figure 7. Figure 8.
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20 30 40 50 60 70 80 90 100
DUTY CYCLE (%) = [1 - EFF*(VIN / VOUT)]
0
500
1000
1500
2000
2500
3000
SW CURRENT LIMIT (mA)
VIN = 5V
VIN = 3.3V
VIN = 2.7V
VIN = 3V
OSCILLATOR FREQUENCY (MHz)
1.4
1.42
1.44
1.46
1.48
1.5
1.52
1.54
1.56
1.58
TEMPERATURE (oC)
VIN = 5V
VIN = 3.3V
-50 -25 025 50 75 100 125 150
2 2.5 3 3.5 4 4.5 5 5.5
SUPPLY VOLTAGE (V)
0
2
4
6
8
10
12
SUPPLY CURRENT (mA)
20 100 1k 20k
FREQUENCY (Hz)
-28
-24
-20
-16
-12
-8
-4
0
4
8
12
16
20
OUTPUT LEVEL (dB)
2k 5k 10k500200
50
0 1 2 3 4 5 6
OUTPUT VOLTAGE (V)
0
50
100
150
200
250
POWER DISSIPATION (mW)
0 1 2 3 4 5 6
OUTPUT VOLTAGE (V)
0
50
100
150
200
250
300
POWER DISSIPATION (mW)
LM4961, LM4961LQBD
SNAS242K –AUGUST 2004–REVISED MAY 2013
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Typical Performance Characteristics (continued)
Power Dissipation vs Output Power Power Dissipation vs Output Power
VDD = 4.2V, RL= 2μF + 30Ω, f = 1kHz VDD = 3.2V, RL= 2μF + 30Ω, f = 1kHz
Figure 9. Figure 10.
Frequency Response vs Input Capacitor Size
Supply Current vs Supply Voltage RL= 8Ω
RL= 2μF + 30Ω, VIN = 0V, RSOURCE = 50Ωfrom top to bottom: Ci= 1.0μF, Ci= 0.39μF, Ci= 0.039μF
Figure 11. Figure 12.
Switch Current Limit vs Duty Cycle Oscillator Frequency vs Temperature
Figure 13. Figure 14.
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2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5
VIN (V)
0
50
100
150
200
250
300
350
RDS_ON (m:)
MAX DUTY CYCLE (%)
92.1
92.2
92.3
92.4
92.5
92.6
92.7
92.8
92.9
93
TEMPERATURE (oC)
VIN = 5V
VIN = 3.3V
-50 -25 025 50 75 100 125 150
RDS(ON) (:)
-40 -25 025 50 75 100 125
TEMPERATURE (oC)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
Vin = 5V
Vin = 3.3V
FEEDBACK VOLTAGE (V)
1.222
1.223
1.224
1.225
1.226
1.227
1.228
1.229
1.23
1.231
-40 -25 025 50 75 100 125
TEMPERATURE (oC)
TEMPERATURE (oC)
FEEDBACK BIAS CURRENT (PA)
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
-50 -25 025 50 75 100 125 150
LM4961, LM4961LQBD
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SNAS242K –AUGUST 2004–REVISED MAY 2013
Typical Performance Characteristics (continued)
Feedback Voltage vs Temperature Feedback Bias Current vs Temperature
Figure 15. Figure 16.
Max. Duty Cycle vs Temperature - ”X” RDS (ON) vs Temperature
Figure 17. Figure 18.
RDS (ON) vs VDD
Figure 19.
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APPLICATION INFORMATION
BRIDGE CONFIGURATION EXPLANATION
The Audio Amplifier portion of the LM4961 has two internal amplifiers allowing different amplifier configurations.
The first amplifier’s gain is externally configurable, whereas 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 Ri while the
second amplifier’s gain is fixed by the two internal 20kΩresistors. Figure 2 shows that the output of amplifier one
serves as the input to amplifier two. This results in both amplifiers producing signals identical in magnitude, but
out of phase by 180°. Consequently, the differential gain for the Audio Amplifier is
AVD = 2 *(Rf/Ri) (1)
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 classic 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. It provides
differential drive to the load, thus doubling the 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.
The bridge configuration also creates a second advantage over single-ended amplifiers. Since the differential
outputs, Vo1 and Vo2, are biased at 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 possible loudspeaker damage.
BOOST CONVERTER POWER DISSIPATION
At higher duty cycles, the increased ON-time of the switch FET means the maximum output current will be
determined by power dissipation within the LM4961 FET switch. The switch power dissipation from ON-time
conduction is calculated by Equation 3.
PD(SWITCH) = DC x IIND(AVE)2x RDS(ON) (2)
where DC is the duty cycle.
There will be some switching losses as well, so some derating needs to be applied when calculating IC power
dissipation.
MAXIMUM AMPLIFIER 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 amplifier portion of the LM4961 has two operational amplifiers,
the maximum internal power dissipation is 4 times that of a single-ended amplifier. The maximum power
dissipation for a given BTL application can be derived from Equation 2.
PDMAX(AMP) = (2VDD2) / (π2RL) (3)
where
RL= Ro1 + Ro2 (4)
MAXIMUM TOTAL POWER DISSIPATION
The total power dissipation for the LM4961 can be calculated by adding Equation 2 and Equation 3 together to
establish Equation 5:
PDMAX(TOTAL) = (2VDD2) / (π2EFF2RL) (5)
whereEFF = Efficiency of boost converter
RL= Ro1+Ro2
The result from Equation 5 must not be greater than the power dissipation that results from Equation 6:
PDMAX = (TJMAX - TA) / θJA (6)
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For the NJB0028A, θJA = 66°C/W. TJMAX = 125°C for the LM4961. Depending on the ambient temperature, TA, of
the system surroundings, Equation 6 can be used to find the maximum internal power dissipation supported by
the IC packaging. If the result of Equation 5 is greater than that of Equation 6, then either the supply voltage
must be increased, the load impedance increased or TAreduced. For the typical application of a 4.2V power
supply, with a 2uF+30Ωload, the maximum ambient temperature possible without violating the maximum
junction temperature is approximately 109°C provided that device operation is around the maximum power
dissipation point. Thus, for typical applications, power dissipation is not an issue. Power dissipation is a function
of output power and thus, if typical operation is not around the maximum power dissipation point, the ambient
temperature may be increased accordingly. Refer to the Typical Performance Characteristics curves for power
dissipation information for lower output levels.
EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS
The LM4961’s exposed-DAP (die attach paddle) package (NJB) provides a low thermal resistance between the
die and the PCB to which the part is mounted and soldered. The low thermal resistance allows rapid heat
transfer from the die to the surrounding PCB copper traces, ground plane, and surrounding air. The NJB package
should have its DAP soldered to a copper pad on the PCB. The DAP’s PCB copper pad may be connected to a
large plane of continuous unbroken copper. This plane forms a thermal mass, heat sink, and radiation area.
Further detailed and specific information concerning PCB layout, fabrication, and mounting an NJB (WQFN)
package is found in Texas Instruments Package Engineering Group under application note AN-1187 (Literature
Number SNOA401).
SHUTDOWN FUNCTION
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 single-pole, single-throw switch
connected between VDD and Shutdown pins.
BAND SWITCH FUNCTION
The LM4961 features a Band Switch function which allows the user to use one amplifier for both receiver
(earpiece) mode and ringer/loudspeaker mode. When a logic high (VDD) is applied to the Band-SW pin (pin 19)
the amplifier is in ringer mode. This enables the boost converter and sets the externally configurable closed loop
gain selection to BW1. If the Band-SW pin has a logic low (GND) applied to its terminal then the device is in
receiver mode. In this mode the boost converter is disabled and the gain selection is switched to BW2. This
allows the amplifier to be powered directly from the battery minus the voltage drop across the Schottky diode.
REDUCING TRANSIENT CURRENT SPIKE
Due to the quick turn-on time of the Boost Converter, a transient supply current spike is observed on shutdown
release. To reduce the rise time of the output voltage (V1), thus reducing the value of the supply current spike,
please refer to application circuit in Figure 20. Using this configuration will allow the user to reduce the transient
supply current spike without the Boost Converter experiencing any stability issues.
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Shutdown 1
GND
12
6
GND
7
114
SW
VDD
L1
10 PH
FB
8
470 pF
13k
SW-Out
1
68k
Shutdown 1
Band-SW
19
Band-SW
Shutdown 2
3
Shutdown 2
4.7 PF
SW GND 28
Vamp 26
1.0 PF
GND 24
1.0 PF
Bypass
2
15
VO2 27
15
VO1 23 2 PF
Ceramic
20k
Cchg
17
VIN
18
0.1 PF
Audio
In
20k
2000 pF
200k
82 pF
BW2BW1
2120
VDD
42k
6800 pF
VI = VFB(1 + R2/(R3 + 170))
Load
C2
1 PF
R2
D1
CF
R3
CO1
CBYPASS
CiRi
CF3
RF3 CF1 CF2
RF1 RF2
CS2
Rc
1k
C3-1
0.01 PF
RC3-1
20k
RC2-1
4.7
C2-1
4.7 PF
LM4961, LM4961LQBD
SNAS242K –AUGUST 2004–REVISED MAY 2013
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Figure 20. Transient Current Spike Reduction Configuration
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications using integrated power amplifiers, and switching DC-DC
converters, is critical for optimizing device and system performance. Consideration to component values must be
used to maximize overall system quality.
The best capacitors for use with the switching converter portion of the LM4961 are multi-layer ceramic
capacitors. They have the lowest ESR (equivalent series resistance) and highest resonance frequency, which
makes them optimum for high frequency switching converters.
When selecting a ceramic capacitor, only X5R and X7R dielectric types should be used. Other types such as
Z5U and Y5F have such severe loss of capacitance due to effects of temperature variation and applied voltage,
they may provide as little as 20% of rated capacitance in many typical applications. Always consult capacitor
manufacturer’s data curves before selecting a capacitor. High-quality ceramic capacitors can be obtained from
Taiyo-Yuden.
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 V1 and VDD pins should be as close to the device as possible.
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SELECTING INPUT CAPACITOR FOR AUDIO AMPLIFIER
One of the major considerations is the closed loop bandwidth of the amplifier. To a large extent, the bandwidth is
dictated by the choice of external components shown in Figure 2. The input coupling capacitor, Ci, 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.
High value input capacitors are both expensive and space hungry in portable designs. Clearly, a certain value
capacitor is needed to couple in low frequencies without severe attenuation. But ceramic speakers used in
portable systems, whether internal or external, have little ability to reproduce signals below 100Hz to 150Hz.
Thus, using a high value input capacitor may not increase actual system performance.
In addition to system cost and size, click and pop performance is affected by the value of the input coupling
capacitor, Ci. A high value 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 value based on desired low frequency response, turn-on pops can be
minimized.
SELECTING BYPASS CAPACITOR FOR AUDIO AMPLIFIER
Besides minimizing the input capacitor value, careful consideration should be paid to the bypass capacitor value.
Bypass capacitor, CB, is the most critical component to minimize turn-on pops since it determines how fast the
amplifier turns on. The slower the amplifier’s outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the
smaller the turn-on pop. Choosing CBequal to 1.0µF along with a small value of Ci(in the range of 0.039µF to
0.39µF), should produce a virtually clickless and popless shutdown function. Although the device will function
properly, (no oscillations or motorboating), with CBequal to 0.1µF, the device will be much more susceptible to
turn-on clicks and pops. Thus, a value of CBequal to 1.0µF is recommended in all but the most cost sensitive
designs.
SELECTING FEEDBACK CAPACITOR FOR AUDIO AMPLIFIER
The LM4961 is unity-gain stable which gives the designer maximum system flexibility. However, to drive ceramic
speakers, a typical application requires a closed-loop differential gain of 10. In this case a feedback capacitor
(Cf2) will be needed as shown in Figure 1 to bandwidth limit the amplifier.
This feedback capacitor creates a low pass filter that eliminates possible high frequency noise. Care should be
taken when calculating the -3dB frequency because an incorrect combination of Rfand Cf2 will cause rolloff
before the desired frequency
SELECTING VALUE FOR RC
The audio power amplifier integrated in the LM4961 is designed for very fast turn on time. The Cchg pin allows
the input capacitors (CinA and CinB) to charge quickly to improve click/pop performance. Rchg1 and Rchg2
protect the Cchg pins from any over/under voltage conditions caused by excessive input signal or an active input
signal when the device is in shutdown. The recommended value for Rchg1 and Rchg2 is 1kΩ. If the input signal
is less than VDD+0.3V and greater than -0.3V, and if the input signal is disabled when in shutdown mode, Rchg1
and Rchg2 may be shorted out.
SELECTING OUTPUT CAPACITOR (CO) FOR BOOST CONVERTER
A single 4.7µF to 10µF ceramic capacitor will provide sufficient output capacitance for most applications. If larger
amounts of capacitance are desired for improved line support and transient response, tantalum capacitors can
be used. Aluminum electrolytics with ultra low ESR such as Sanyo Oscon can be used, but are usually
prohibitively expensive. Typical AI electrolytic capacitors are not suitable for switching frequencies above 500
kHz because of significant ringing and temperature rise due to self-heating from ripple current. An output
capacitor with excessive ESR can also reduce phase margin and cause instability.
In general, if electrolytics are used, we recommended that they be paralleled with ceramic capacitors to reduce
ringing, switching losses, and output voltage ripple.
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SELECTING INPUT CAPACITOR (Cs1) FOR BOOST CONVERTER
An input capacitor is required to serve as an energy reservoir for the current which must flow into the coil each
time the switch turns ON. This capacitor must have extremely low ESR, so ceramic is the best choice. We
recommend a nominal value of 4.7µF, but larger values can be used. Since this capacitor reduces the amount of
voltage ripple seen at the input pin, it also reduces the amount of EMI passed back along that line to other
circuitry.
SETTING THE OUTPUT VOLTAGE (V1) OF BOOST CONVERTER
The output voltage is set using the external resistors R2and R3(see Figure 2). A value of approximately 13.3kΩ
is recommended for R3to establish a divider current of approximately 92µA. R2is calculated using the formula:
V1= VFB [1 + R2(R3+ 170)] (7)
FEED-FORWARD COMPENSATION FOR BOOST CONVERTER
Although the LM4961's internal Boost converter is internally compensated, the external feed-forward capacitor Cf
is required for stability (see Figure 2). Adding this capacitor puts a zero in the loop response of the converter.
The recommended frequency for the zero fz should be approximately 6kHz. Cf1 can be calculated using the
formula:
Cf1 = 1 / (2πx R1x fz) (8)
SELECTING DIODES
The external diode used in Figure 2 should be a Schottky diode. A 20V diode such as the MBR0520 from
Fairchild Semiconductor is recommended.
The MBR05XX series of diodes are designed to handle a maximum average current of 0.5A. For applications
exceeding 0.5A average but less than 1A, a Microsemi UPS5817 can be used.
DUTY CYCLE
The maximum duty cycle of the boost converter determines the maximum boost ratio of output-to-input voltage
that the converter can attain in continuous mode of operation. The duty cycle for a given boost application is
defined as:
Duty Cycle = VOUT + VDIODE - VIN/VOUT + VDIODE - VSW
This applies for continuous mode operation.
INDUCTANCE VALUE
The first question we are usually asked is: “How small can I make the inductor.” (because they are the largest
sized component and usually the most costly). The answer is not simple and involves trade-offs in performance.
Larger inductors mean less inductor ripple current, which typically means less output voltage ripple (for a given
size of output capacitor). Larger inductors also mean more load power can be delivered because the energy
stored during each switching cycle is:
E = L/2 x (lp)2 (9)
Where “lp” is the peak inductor current. An important point to observe is that the LM4961 will limit its switch
current based on peak current. This means that since lp(max) is fixed, increasing L will increase the maximum
amount of power available to the load. Conversely, using too little inductance may limit the amount of load
current which can be drawn from the output.
Best performance is usually obtained when the converter is operated in “continuous” mode at the load current
range of interest, typically giving better load regulation and less output ripple. Continuous operation is defined as
not allowing the inductor current to drop to zero during the cycle. It should be noted that all boost converters shift
over to discontinuous operation as the output load is reduced far enough, but a larger inductor stays “continuous”
over a wider load current range.
To better understand these trade-offs, a typical application circuit (5V to 12V boost with a 10µH inductor) will be
analyzed. We will assume:
VIN = 5V, VOUT = 12V, VDIODE = 0.5V, VSW = 0.5V (10)
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Since the frequency is 1.6MHz (nominal), the period is approximately 0.625µs. The duty cycle will be 62.5%,
which means the ON-time of the switch is 0.390µs. It should be noted that when the switch is ON, the voltage
across the inductor is approximately 4.5V. Using Equation 11:
V = L (di/dt) (11)
We can then calculate the di/dt rate of the inductor which is found to be 0.45 A/µs during the ON-time. Using
these facts, we can then show what the inductor current will look like during operation:
Figure 21. 10μH Inductor Current
5V - 12V Boost (LM4961X)
During the 0.390µs ON-time, the inductor current ramps up 0.176A and ramps down an equal amount during the
OFF-time. This is defined as the inductor “ripple current”. It can also be seen that if the load current drops to
about 33mA, the inductor current will begin touching the zero axis which means it will be in discontinuous mode.
A similar analysis can be performed on any boost converter, to make sure the ripple current is reasonable and
continuous operation will be maintained at the typical load current values. Taiyo-Yudens NR4012 inductor series
is recommended.
MAXIMUM SWITCH CURRENT
The maximum FET switch current available before the current limiter cuts in is dependent on duty cycle of the
application. This is illustrated in a graph in the typical performance characterization section which shows typical
values of switch current as a function of effective (actual) duty cycle.
CALCULATING OUTPUT CURRENT OF BOOST CONVERTER (IAMP)
As shown in Figure 2 which depicts inductor current, the load current is related to the average inductor current by
the relation:
ILOAD = IIND(AVG) x (1 - DC) (12)
Where "DC" is the duty cycle of the application. The switch current can be found by:
ISW = IIND(AVG) + 1/2 (IRIPPLE) (13)
Inductor ripple current is dependent on inductance, duty cycle, input voltage and frequency:
IRIPPLE = DC x (VIN-VSW) / (f x L) (14)
combining all terms, we can develop an expression which allows the maximum available load current to be
calculated:
ILOAD(max) = (1–DC)x(ISW(max)–DC(VIN-VSW))/2FL (15)
The equation shown to calculate maximum load current takes into account the losses in the inductor or turn-OFF
switching losses of the FET and diode.
DESIGN PARAMETERS VSW AND ISW
The value of the FET "ON" voltage (referred to as VSW in Equation 12 thru Equation 15) is dependent on load
current. A good approximation can be obtained by multiplying the "ON Resistance" of the FET times the average
inductor current.
FET on resistance increases at VIN values below 5V, since the internal N-FET has less gate voltage in this input
voltage range (see Typical Performance Characteristics curves). Above VIN = 5V, the FET gate voltage is
internally clamped to 5V.
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The maximum peak switch current the device can deliver is dependent on duty cycle. For higher duty cycles, see
Typical Performance Characteristics curves.
INDUCTOR SUPPLIERS
The recommended inductors for the LM4961 is the Taiyo-Yuden NR4012. When selecting an inductor, make
certain that the continuous current rating is high enough to avoid saturation at peak currents. A suitable core type
must be used to minimize core (switching) losses, and wire power losses must be considered when selecting the
current rating.
PCB LAYOUT GUIDELINES
High frequency boost converters require very careful layout of components in order to get stable operation and
low noise. All components must be as close as possible to the LM4961 device. It is recommended that a 4-layer
PCB be used so that internal ground planes are available. See Figures 22-25 for demo board reference
schematic and layout.
Some additional guidelines to be observed:
1. Keep the path between L1, D1, and Co extremely short. Parasitic trace inductance in series with D1 and Co
will increase noise and ringing.
2. The feedback components R1, R2 and Cf1 must be kept close to the FB pin of U1 to prevent noise injection
on the FB pin trace.
3. If internal ground planes are available (recommended) use vias to connect directly to ground at pin 2 of U1, as
well as the negative sides of capacitors Cs1 and Co.
GENERAL MIXED-SIGNAL LAYOUT RECOMMENDATION
This section provides practical guidelines for mixed signal PCB layout that involves various digital/analog power
and ground traces. Designers should note that these are only "rule-of-thumb" recommendations and the actual
results will depend heavily on the final layout.
Power and Ground Circuits
For 2 layer mixed signal design, it is important to isolate the digital power and ground trace paths from the
analog power and ground trace paths. Star trace routing techniques (bringing individual traces back to a central
point rather than daisy chaining traces together in a serial manner) can have a major impact on low level signal
performance. Star trace routing refers to using individual traces to feed power and ground to each circuit or even
device. This technique will take require a greater amount of design time but will not increase the final price of the
board. The only extra parts required may be some jumpers.
Single-Point Power / Ground Connection
The analog power traces should be connected to the digital traces through a single point (link). A "Pi-filter" can
be helpful in minimizing high frequency noise coupling between the analog and digital sections. It is further
recommended to place digital and analog power traces over the corresponding digital and analog ground traces
to minimize noise coupling.
Placement of Digital and Analog Components
All digital components and high-speed digital signals traces should be located as far away as possible from
analog components and circuit traces.
Avoiding Typical Design / Layout Problems
Avoid ground loops or running digital and analog traces parallel to each other (side-by-side) on the same PCB
layer. When traces must cross over each other do it at 90 degrees. Running digital and analog traces at 90
degrees to each other from the top to the bottom side as much as possible will minimize capacitive noise
coupling and crosstalk.
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Shutdown 1
GND
12
6
GND
7
114
SW
VDD
L1
10 PH
FB
8
470 pF
13k
SW-Out
1
68k
Band-SW
19
Shutdown 2
3
4.7 PF
SW GND 28
4.7 PF
Vamp 26
4.7 PF
GND 24
1.0 PF
Bypass
2
15
VO2 27
15
VO1 23 2 PF
Ceramic
20k
Cchg
17
VIN
18
0.1 PF
Audio In
20k
2000 pF
200k
82 pF
BW2BW1
2120
VDD
42k
6800 pF
VI = VFB(1 + R2/(R3 + 170))
Load
C2
R2
D2
C3
R3
CS1
Cb
CINARINA
CFB
RFBCF2 CFA
RF2 RFA
CS2
Rc
1k
VDD
RPU1
J3
VDD
RPU3
J6
VDD
RPU2
J5
LM4961, LM4961LQBD
www.ti.com
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Schematic Board Layout
Figure 22. Demo Board Schematic
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Demonstration Board Layout
Figure 23. Recommended TS SE PCB Layout: Top Silkscreen
Figure 24. Recommended TS SE PCB Layout: Top Layer
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REVISION HISTORY
Rev Date Description
1.0 08/25/04 Initial WEB.
1.1 11/14/05 Replaced graphics 83, C4, and C5 with 01, 02, and 03), then WEB.
1.2 08/30/06 Added the TWUA row in the 4.2V Elect. Char table, then released the D/S to the WEB.
1.3 09/11/06 Added the “Selecting Value For Rc” in the Apps section, then released to the WEB.
Changes from Revision J (May 2013) to Revision K Page
• Changed layout of National Data Sheet to TI format .......................................................................................................... 17
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PACKAGE OPTION ADDENDUM
www.ti.com 1-Oct-2016
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead/Ball Finish
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LM4961LQ/NOPB OBSOLETE WQFN NJB 28 TBD Call TI Call TI L4961LQ
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
MECHANICAL DATA
NJB0028A
www.ti.com
LQA28A (REV B)
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