LM4804
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LM4804 Boomer™ Audio Power Amplifier SerieLow Voltage High Power Audio Power
Amplifier
Check for Samples: LM4804
FEATURES
DESCRIPTION
•
The LM4804 integrates a Boost Converter with an
Audio Power Amplifier to drive voice coil speakers in
portable applications. When powered by a 3V supply,
it is capable of creating 1.8W power dissipation in an
8Ω bridge-tied-load (BTL) with less than 1% THD+N.
1
23
•
•
•
•
•
•
Pop & Click Circuitry Eliminates Noise During
Turn-On and Turn-Off Transitions
Low, 2μA (Max) Shutdown Current
Low, 11mA (Typ) Quiescent Current (VDD =
4.2V, RL = 8Ω)
1.8W Mono BTL Output, RL = 8Ω, VDD = 3V
Short Circuit Protection
Unity-Gain Stable
External Gain Configuration Capability
Boomer audio power amplifiers were designed
specifically to provide high quality output power with a
minimal amount of external components. The
LM4804 does not require bootstrap capacitors, or
snubber circuits. Therefore it is ideally suited for
portable applications requiring high output voltage
and minimal size.
APPLICATIONS
•
•
The LM4804 features a micro-power shutdown mode.
Additionally, the LM4804 features an internal thermal
shutdown protection mechanism.
Cellphone
PDA
The LM4804 contains advanced pop & click circuitry
that eliminates output transients which would
otherwise occur during power or shutdown cycles.
KEY SPECIFICATIONS
•
•
•
Quiescent Power Supply Current (VDD = 4.2V,
RL = 8Ω), 11mA (Typ)
BTL Output Power (RL = 8Ω, 2% THD+N, VDD =
3V), 1.8W (Typ)
Shutdown Current, 2µA (Max)
The LM4804 is unity-gain stable. Its closed-loop gain
is determined by the value of external, user selected
resistors.
FB
FREQ
SD1
GND2
NC
NC
GND3
Connection Diagram
28
27
26
25
24
23
22
NC
1
21
NC
NC
2
20
NC
GND1
3
19
BYPASS
NC
4
18
SD2
NC
8
9
10
11
12
13
14
NC
15
VO2
7
V1
NC
SW
VO1
NC
16
NC
17
6
IN-
5
IN+
VDD
BOOT
Figure 1. LM4804LQ (5x5)
Top View
See Package Number NJB0028A
1
2
3
Please 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.
Boomer is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
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LM4804
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Typical Application
D1
L1
4.7 PH
Cs1
4.7 PF
Bat
VDD
R3
150k
C3
4.7 pF
3
25
26
S/D
27
Cf1
470 pF
5
7
VDD
SW
GND1
V1 = VFB (1 + R1/R2)
FB
Co
100 PF
R1
301k
28
R2
78.7k
GND2
S/D1
BOOT
6
FREQ
10 PH
0.1 PF
18
19
Cb
1.0 PF
9
V1
S/D2
Bypass
GND3
+IN
VO2
12
22
Cs2
4.7 PF
14
8:
20k
Audio In
0.1 PF
Ci
8
-IN
VO1
11
Ri
Rf
200k
Figure 2. Typical LM4804 Audio Amplifier Application Circuit
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.
2
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Absolute Maximum Ratings (1) (2) (3)
Supply Voltage (VDD)
6.5V
Supply Voltage (V1)
6.5V
−65°C to +150°C
Storage Temperature
−0.3V to VDD + 0.3V
Input Voltage
(4)
Internally limited
ESD Susceptibility (5)
2000V
ESD Susceptibility (6)
200V
Power Dissipation
Junction Temperature
125°C
θJA (WQFN)
Thermal Resistance
59°C/W
See AN-1187 'Leadless Leadframe Packaging (WQFN)'.
(1)
(2)
(3)
(4)
(5)
(6)
All voltages are measured with respect to the GND pin, unless otherwise specified.
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 specify 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.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
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.
Human body model, 100pF discharged through a 1.5kΩ resistor.
Machine Model, 220pF – 240pF discharged through all pins.
Operating Ratings
TMIN ≤ TA ≤ TMAX
Temperature Range
−40°C ≤ TA ≤ +85°C
3V ≤ VDD ≤ 5V
Supply Voltage (VDD)
2.7V ≤ V1 ≤ 6.1V
Supply Voltage (V1)
Electrical Characteristics VDD = 4.2V (1) (2)
The following specifications apply for VDD = 4.2V, V1 = 6.0V, AV-BTL = 20dB, RL = 8Ω, fIN = 1kHz, CB = 1.0µF, R1 = 301kΩ, R2 =
78.7kΩ unless otherwise specified. Limits apply for TA = 25°C. See Figure 2
Symbol
Parameter
Conditions
LM4804
Typical
(3)
Limit
(4) (5)
Units
(Limits)
IDD
Quiescent Power Supply Current
VIN = 0, RLOAD = ∞
11
22
mA (max)
ISD
Shutdown Current
VSHUTDOWN = GND (6) (7)
0.1
2
µA (max)
VSDIH
Shutdown Voltage Input High
SD1
SD2
0.7VDD
1.4
V (min)
VSDIL
Shutdown Voltage Input Low
SD1
SD2
0.15VDD
0.4
V (max)
TWU
Wake-up Time
CB = 1.0µF
VOS
Output Offset Voltage
TSD
Thermal Shutdown Temperature
POUT
Output Power
(1)
(2)
(3)
(4)
(5)
(6)
(7)
70
4
THD = 2% (max)
1.9
msec (max)
40
mV (max)
125
°C (min)
1.7
W (min)
All voltages are measured with respect to the GND pin, unless otherwise specified.
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 specify 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.
Typicals are measured at 25°C and represent the parametric norm.
Limits are specified to Texas Instruments' AOQL (Average Outgoing Quality Level).
Datasheet min/max specification limits are ensured by design, test, or statistical analysis.
Shutdown current is measured in a normal room environment. The Shutdown pin should be driven as close as possible to Vin for
minimum shutdown current.
Shutdown current is measured with components R1 and R2 removed.
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Electrical Characteristics VDD = 4.2V(1)(2) (continued)
The following specifications apply for VDD = 4.2V, V1 = 6.0V, AV-BTL = 20dB, RL = 8Ω, fIN = 1kHz, CB = 1.0µF, R1 = 301kΩ, R2 =
78.7kΩ unless otherwise specified. Limits apply for TA = 25°C. See Figure 2
Symbol
Parameter
Conditions
THD+N
Total Harmomic Distortion + Noise
POUT = 1.5W
εOS
Output Noise
A-Weighted Filter, VIN = 0V,
Input Referred
PSRR
Power Supply Rejection Ratio
VRIPPLE = 200mVp-p
f = 217Hz
f = 1kHz
VFB
4
Feedback Pin Reference Voltage
LM4804
Typical (3)
Limit (4) (5)
0.13
0.5
22
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%
µV
72
67
1.24
Units
(Limits)
dB (min)
1.2772
1.2028
V (max)
V (min)
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Electrical Characteristics VDD = 3.0V (1) (2)
The following specifications apply for VDD = 3.0V, V1 = 6.0V, AV-BTL = 20dB, RL = 8Ω, fIN = 1kHz, CB = 1.0µF, R1 = 301kΩ, R2 =
78.7kΩ unless otherwise specified. Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LM4804
Typical (3)
Limit (4) (5)
Units
(Limits)
IDD
Quiescent Power Supply Current
VDD = 3.2V, VIN = 0, RLOAD = ∞
19
33
mA (max)
ISD
Shutdown Current
VSHUTDOWN = GND (6) (7)
0.1
2
µA (max)
VSDIH
Shutdown Voltage Input High
SD1
SD2
0.7VDD
1.4
V (min)
VSDIL
Shutdown Voltage Input Low
SD1
SD2
0.15VDD
0.4
V (max)
TWU
Wake-up Time
CB = 1.0µF
VOS
Output Offset Voltage
TSD
Thermal Shutdown Temperature
POUT
Output Power
THD = 2% (max)
THD+N
Total Harmomic Distortion + Noise
POUT = 1.5W
εOS
Output Noise
A-Weighted Filter, VIN = 0V,
Input Referred
PSRR
Power Supply Rejection Ratio
VRIPPLE = 200mVp-p
f = 217Hz
f = 1kHz
VFB
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
Feedback Pin Reference Voltage
70
3
See (8)
msec (max)
40
mV (max)
125
°C (min))
1.8
1.65
W (min)
0.15
0.5
%
30
µV
73
66
dB (min)
1.24
1.2772
1.2028
V (max)
V (min)
All voltages are measured with respect to the GND pin, unless otherwise specified.
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 specify 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.
Typicals are measured at 25°C and represent the parametric norm.
Limits are specified to Texas Instruments' AOQL (Average Outgoing Quality Level).
Datasheet min/max specification limits are ensured by design, test, or statistical analysis.
Shutdown current is measured in a normal room environment. The Shutdown pin should be driven as close as possible to Vin for
minimum shutdown current.
Shutdown current is measured with components R1 and R2 removed.
Feedback pin reference voltage is measured with the Audio Amplifier disconnected from the Boost converter (the Boost converter is
unloaded).
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Typical Performance Characteristics
THD+N vs Frequency
VDD = 4.2V, RL = 8Ω, POUT = 1.5W
THD+N vs Frequency
VDD = 3.0V, RL = 8Ω, POUT = 1.5W
60
20
20
5
10
2
5
THD+N (%)
THD + N (%)
10
1
0.5
0.2
2
1
0.5
0.2
0.1
0.1
0.05
0.05
0.02
0.02
0.01
20
0.01
20
50 100 200 500 1k 2k
5k 10k 20k
FREQUENCY (Hz)
5k 10k 20k
FREQUENCY (Hz)
Figure 3.
10
50 100 200 500 1k 2k
Figure 4.
THD+N vs Output Power
VDD = 4.2V, RL = 8Ω, f = 1kHz
10
THD+N vs Output Power
VDD = 3.0V, RL = 8Ω
5
5
2
THD+N (%)
THD+N (%)
2
1
0.5
1
0.5
0.2
0.1
0.05
0.2
0.02
0.1
10m 20m 50m 100m 200m 500m 1
0.01
10m 20m 50m 100m 200m 500m 1
2 3
6
90
Figure 6.
PSRR vs Frequency
VDD = 3V, Input Referred
PSRR vs Frequency
VDD = 4.2V, Input Referred
80
70
60
50
40
20
50 100 200 500 1k 2k
2 3
OUTPUT POWER (W)
Figure 5.
POWER SUPPLY REJECTION RATIO (dB)
POWER SUPPLY REJECTION RATIO (dB)
OUTPUT POWER (W)
5k 10k 20k
90
80
70
60
50
40
20
50 100 200 500 1k 2k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 7.
Figure 8.
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Typical Performance Characteristics (continued)
25
Power Supply Current
vs Power Supply Voltage
RL = 8Ω
Power Supply Current
vs Output Power
1600
POWER SUPPLY CURRENT (mA)
POWER SUPPLY CURRENT (mA)
THD+N = 10%
20
15
10
5
0
2.6
2.8
3
3.2
3.4 3.6
3.8
4
1400
THD+N = 1%
1200
1000
VDD = 3.0V
800
VDD = 3.6V
600
400
VDD = 4.2V
200
0
4.2
0
0.5
1
Figure 9.
Output Power
vs Power Supply Voltage
RL = 8Ω
3.50
THD+N = 10%
OUTPUT POWER (W)
2
THD+N = 1%
1.5
1
0.5
0
2.6
2.8
3
3.2
3.4 3.6
3.8
4
3.00
RL = 4:
2.50
2.00
THD+N = 1%
1.50
THD+N = 10%
1.00
RL = 8:
0.50
0.00
0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50
4.2
POWER SUPPLY VOLTAGE (V)
LOAD DISSIPATION (W)
Figure 11.
Figure 12.
VFB vs Temperature
1.2365
95.0
10mA
1.236
1.2355
85.0
V FB (V)
Efficiency (%)
90.0
80.0
75.0
600mA
V DD = 3.3V
1.235
1.2345
1.234
70.0
60.0
1.8
2.5
Amplifier Circuit Dissipation
vs Load Dissipation
Efficiency vs VIN
VOUT = 5.0V
65.0
2
Figure 10.
AMPLIFIER CIRCUIT DISSIPATION (W)
2.5
1.5
OUTPUT POWER (W)
POWER SUPPLY VOLTAGE (V)
1.2335
300mA
1.233
2.1 2.4 2.7 3.0 3.3
3.6 3.9 4.2 4.5
Vin
1.2325
-40
-25
-10
5
20
35
50
65
80
TEMPERATURE (ºC)
Figure 13.
Figure 14.
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Typical Performance Characteristics (continued)
Frequency vs VIN
300k
1.5
150
1
0.5
1.100
1.00
0
0.90
0
0
1.2
1.20
0
Start-Up Voltage
Frequency (Mhz)
225k
75k
Maximum Start Up Voltage
vs Temperature
1.30
0
2
1.7
2.2
2.7
3.2
3.7
0.800
-50
4.2
0
50
Vin (V)
Temperatur
e
Figure 15.
Figure 16.
Typical RDS(ON)
vs Temperature
Typical Current Limit
vs Temperature
0.300
100
3.000
2.900
0.250
Current Limit
2.800
Rds on
0.200
0.150
2A
0.100
1A
2.700
2.600
2.500
2.400
2.300
2.200
0.050
2.100
0.000
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80
Temperature (ºC)
Figure 17.
8
2.000
- - - 0 10 20 30 40 50 60 70 80
40 30 20 10
Temperature (ºC)
Figure 18.
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APPLICATION INFORMATION
BRIDGE CONFIGURATION EXPLANATION
Audio Amplifier portion of the LM4804 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 Ri while the second amplifier’s gain is fixed by the two internal 20kΩ resistors. Figure 2 shows that the
output of amplifier one serves as the input to amplifier two which results in both amplifiers producing signals
identical in magnitude, but out of phase by 180°. Consequently, the differential gain for the IC 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 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 closedloop gain without causing excessive clipping, please refer to the Audio Power Amplifier Design section.
A 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.
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 LM4804 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) = 4(VDD)2 / (2π2RL)
(2)
BOOST CONVERTER POWER DISSIPATION
At higher duty cycles, the increased ON time of the FET means the maximum output current will be determined
by power dissipation within the LM2731 FET switch. The switch power dissipation from ON-state conduction is
calculated by Equation 3.
PDMAX(SWITCH) = DC x IIND(AVE)2 x RDS(ON)
(3)
There will be some switching losses as well, so some derating needs to be applied when calculating IC power
dissipation.
TOTAL POWER DISSIPATION
The total power dissipation for the LM4804 can be calculated by adding Equation 2 and Equation 3 together to
establish Equation 4:
PDMAX(TOTAL) = [4*(VDD)2/2π2RL]+[DCxIIND(AVE)2xRDS(ON)]
(4)
The result from Equation 4 must not be greater than the power dissipation that results from Equation 5:
PDMAX = (TJMAX - TA) / θJA
(5)
For package LQA28A, θJA = 59°C/W. TJMAX = 125°C for the LM4804. Depending on the ambient temperature, TA,
of the system surroundings, Equation 5 can be used to find the maximum internal power dissipation supported by
the IC packaging. If the result of Equation 4 is greater than that of Equation 5, then either the supply voltage
must be increased, the load impedance increased or TA reduced. For the typical application of a 3V power
supply, with V1 set to 6.0V and 8Ω load, the maximum ambient temperature possible without violating the
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maximum junction temperature is approximately TBD°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 LM4804’s exposed-DAP (die attach paddle) package (LD) provides a low thermal resistance between the
die and the PCB to which the part is mounted and soldered. This allows rapid heat transfer from the die to the
surrounding PCB copper traces, ground plane, and surrounding air. The LD 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 LD (WQFN) package is available
from Texas Instruments’ Package Engineering Group under application note AN1187.
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, in
conjunction with an external pull-up resistor to drive both shutdown pins simultaneously. When the switch is
closed, the shutdown pin is connected to ground which disables the amplifier. If the switch is open, then the
external pull-up resistor to VDD will enable the LM4804. This scheme ensures that the shutdown pins will not float
thus preventing unwanted state changes.
EXTERNAL COMPONENT SELECTION
Proper selection of external components in applications using integrated power amplifiers, and switching DC-DC
converters, is critical to optimize 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 LM4804 are multi-layer ceramic
capacitors. They have the lowest ESR (equivalent series resistance) and highest resonance frequency which
makes them optimum for use with 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, AVX, and Murata.
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.
SELECTING THE AUDIO AMPLIFIER'S INPUT CAPACITOR
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 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.
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 ceramic 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.
10
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In addition to system cost and size, click and pop performance is effected by the size of the input coupling
capacitor, Ci. 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.
SELECTING THE AUDIO AMPLIFIER'S BYPASS CAPACITOR
Besides minimizing the input capacitor size, 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
amplifer 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 CB equal 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. While the device will function
properly, (no oscillations or motorboating), with CB equal to 0.1µF, the device will be much more susceptible to
turn-on clicks and pops. Thus, a value of CB equal to 1.0µF is recommended in all but the most cost sensitive
designs.
OPERATING PRINCIPLE
The LM4804 includes step-up DC-DC voltage regulation for battery-powered and low-input voltage systems. It
combines a step-up switching regulator, N-channel power MOSFET, built-in current limit, thermal limit, and
voltage reference. The switching DC-DC regulator boosts an input voltage between .8V and 14V to a regulated
output voltage between 1.24V and 14V. The LM4804 starts from a low 1.1V input and remains operational down
to below .8V.
This device is optimized for use in cellular phones and other applications requiring a small size, low profile, as
well as low quiescent current for maximum battery life during stand-by and shutdown.
Additional features include a built-in peak switch current limit, a high-efficiency gated-oscillator topology that
offers an output of up to 2A at low output voltages, and thermal protection circuitry.
Figure 19. Functional Diagram of the LM4804's Regulator
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GATED OSCILLATOR CONTROL SCHEME
The on/off regulation mode of the LM4804, along with its ultra-low quiescent current, results in good efficiency
over a very wide load range. The internal oscillator frequency can be programmed using an external resistor to
be constant or vary with the battery voltage. Adding a capacitor to program the frequency allows the designer to
adjust the duty cycle and optimize it for the application. Adding a resistor in addition to the capacitor allows the
duty cycle to dynamically compensate for changes to the input/output voltage ratio. We call this a Ratio Adaptive
Gated Oscillator circuit. Using the correct RC components to adjust the oscillator allows the part to run with low
ripple and high efficiency over a wide range of loads and input/output voltages.
Figure 20. Typical Step-Up Regulator Waveforms
PULSE FREQUENCY MODULATION (PFM)
Pulse Frequency Modulation is typically accomplished by switching continuously until the voltage limit is reached
and skipping cycles after that to just maintain it. This results in a somewhat hysteretic mode of operation. The
coil stores more energy each cycle as the current ramps up to high levels. When the voltage limit is reached, the
system usually overshoots to a higher voltage than required, due to the stored energy in the coil (see Figure 20).
The system will also undershoot somewhat when it starts switching again because it has depleted all the stored
energy in the coil and needs to store more energy to reach equilibrium with the load. Larger output capacitors
and smaller inductors reduce the ripple in these situations. The frequency being filtered, however, is not the basic
switching frequency. It is a lower frequency determined by the load, the input/output voltage and the circuit
parameters. This mode of operation is useful in situations where the load variation is significant. Power managed
computer systems, for instance, may vary from zero to full load while the system is on and this is usually the
preferred regulation mode for such systems.
CYCLE TO CYCLE PFM
When the load doesn't vary over a wide range (like zero to full load), ratio adaptive circuit techniques can be
used to achieve cycle to cycle PFM regulation and lower ripple (or smaller output capacitors). The key to success
here is matching the duty cycle of the circuit closely to what is required by the input to output voltage ratio. This
ratio then needs to be dynamically adjusted for input voltage changes (usually caused by batteries running
down). The chosen ratio should allow most of the energy in each switching cycle to be delivered to the load and
only a small amount to be stored. When the regulation limit is reached, the overshoot will be small and the
system will settle at an equilibrium point where it adjusts the off time in each switching cycle to meet the current
requirements of the load. The off time adjustment is done by exceeding the regulation limit during each switching
cycle and waiting until the voltage drops below the limit again to start the next switching cycle. The current in the
coil never goes to zero like it frequently does in the hysteretic operating mode of circuits with wide load variations
or duty cycles that aren't matched to the input/output voltage ratio. Optimizing the duty cycle for a given set of
input/output voltages conditions can be done by using the circuit values in the Application Notes.
12
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LOW VOLTAGE START-UP
The LM4804 can start-up from voltages as low as 1.1 volts. On start-up, the control circuitry switches the Nchannel MOSFET continuously until the output reaches 3 volts. After this output voltage is reached, the normal
step-up regulator feedback and gated oscillator control scheme take over. Once the device is in regulation, it can
operate down to below .8V input, since the internal power for the IC can be boot-strapped from the output using
the Vdd pin.
SHUT DOWN
The LM4804 features a shutdown mode that reduces the quiescent current to less than a 2.5uA over
temperature. This extends the life of the battery in battery powered applications. During shutdown, all feedback
and control circuitry is turned off. The regulator's output voltage drops to one diode drop below the input voltage.
Entry into the shutdown mode is controlled by the active-low logic input pin S/D1 (pin 26). When the logic input to
this pin is pulled below 0.15VDD, the device goes into shutdown mode. The logic input to this pin should be above
0.7VDD for the device to work in normal step-up mode.
SELECTING OUTPUT CAPACITOR (CO) FOR BOOST CONVERTER
A single ceramic capacitor of value 4.7µF to 10µF 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 due to 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, it is recommended that they be paralleled with ceramic capacitors to reduce
ringing, switching losses, and output voltage ripple.
INTERNAL CURRENT LIMIT AND THERMAL PROTECTION
An internal cycle-by-cycle current limit serves as a protection feature. This is set high enough (2.85A typical,
approximately 4A maximum) so as not to come into effect during normal operating conditions. An internal thermal
protection circuit disables the MOSFET power switch when the junction temperature (TJ) exceeds about 160°C.
The switch is re-enabled when TJ drops below approximately 135°C.
NON-LINEAR EFFECT
The LM4804 takes advantage of a non-linear effect that allows for the duty cycle to be programmable. The C3
capacitor is used to dump charge on the FREQ pin in order to manipulate the duty cycle of the internal oscillator.
The part is being tricked to behave in a certain manner, in the effort to make this Pulse Frequency Modulated
(PFM) boost switching regulator behave as a Pulse Width Modulated (PWM) boost switching regulator.
CHOOSING THE CORRECT C3 CAPACITOR
The C3 capacitor allows for the duty cycle of the internal oscillator to be programmable. Choosing the correct C3
capacitor to get the appropriate duty cycle for a particular application circuit is a trial and error process. The nonlinear effect that C3 produces is dependent on the input voltage and output voltage values. The correct C3
capacitor for particular input and output voltage values cannot be calculated. Choosing the correct C3
capacitance is best done by trial and error, in conjunction with the checking of the inductor peak current to make
sure your not too close to the current limit of the device. As the C3 capacitor value increases, so does the duty
cycle. And conversely as the C3 capacitor value decreases, the duty cycle decreases. An incorrect choice of the
C3 capacitor can result in the part prematurely tripping the current limit and/or double pulsing, which could lead
to the output voltage not being stable.
SETTING THE OUTPUT VOLTAGE
The output voltage of the step-up regulator can be set by connecting a feedback resistive divider made of RF1
and RF2. The resistor values are selected as follows:
R1 = R2[(VOUT/1.24) −1]
(6)
A value of 50k to 100k is suggested for R2. Then, R1 can be selected using Equation 6.
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VDD SUPPLY
The Vdd supply must be between 3 to 5 volts for the LM4804. This voltage can be bootstrapped from a much
lower input voltage by simply connecting the VDD pin to VOUT. In the event that the VDD supply voltage is not a
low ripple voltage source (less than 200 millivolts), it may be advisable to use an RC filter to clean it up.
Excessive ripple on VDD may reduce the efficiency.
SETTING THE SWITCHING FREQUENCY
The switching frequency of the oscillator is selected by choosing an external resistor (R3) connected between VIN
and the FREQ pin. See the graph titled "Frequency vs VIN” in the Typical Performance Characteristics section of
the data sheet for choosing the R3 value to achieve the desired switching frequency. A high switching frequency
allows the use of very small surface mount inductors and capacitors and results in a very small solution size. A
switching frequency between 300kHz and 2MHz is recommended.
OUTPUT DIODE SELECTION
A Schottky diode should be used for the output diode. The forward current rating of the diode should be higher
than the peak input current, and the reverse voltage rating must be higher than the output voltage. Do not use
ordinary rectifier diodes, since slow switching speeds and long recovery times cause the efficiency and the load
regulation to suffer. Table 1 shows a list of the diode manufacturers.
WQFN PACKAGE DEVICES
The LM4804 is offered in the 14 lead WQFN surface mount package to allow for increased power dissipation
compared to the MSOP-8. For details of the thermal performance as well as mounting and soldering
specifications, refer to Application Note AN-1187.
RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT
Figure 22 through Figure 27 show the recommended four-layer PC board layout that is optimized for the LQpackaged, 3V 1.7W LM4804 mono-BTL audio amplifier and its associated external components. This circuit is
designed for use with an external 3V to 4.2V supply and speakers with 4Ω or higher impedance (8Ω nominal).
The LM4804 circuit board is easy to use. Apply between 3V and 4.2V (equivalent to, respectfully, a discharged or
a fully charged Li-ion or NMH battery) and ground to JP2's VDD and GND pins, respectively. Connect a speaker
with an impedance of 4Ω or greater (8Ω nominal) between the board’s VO1 (-) and VO2 (+) pins. An audio signal
is applied to JP1 between the VIN (+) and GND (-) pins.
The circuit board is configured for a gain of 20 or 26dB (VO2 -VO1 with respect to VIN). An inverting gain of -10
at VO1 is set by Rf (200kΩ) versus Ri (20kΩ). The extra gain of 2 is a product of the BTL output (VO2 - VO1).
Gain can be modified by changing Rf's value with respect to Ri.
Table 1. Suggested Manufacturers List
Inductors
Capacitors
Diodes
Coilcraft
Tel: (800) 322-2645
Fax: (708) 639-1469
Sprague/ Vishay
Tel: (207) 324-4140
Fax: (207) 324-7223
Motorola
Tel: (800) 521-6274
Fax: (602) 244-6609
Coiltronics
Tel: (407) 241-7876
Fax: (407) 241-9339
Kemet
Tel: (864) 963-6300
Fax: (864) 963-6521
International Rectifier (IR)
Tel: (310) 322-3331
Fax: (310) 322-3332
Pulse Engineering
Tel: (619) 674-8100
Fax: (619) 674-8262
Nichicon
Tel: (847) 843-7500
Fax: (847) 843-2798
General Semiconductor
Tel: (516) 847-3222
Fax: (516) 847-3150
14
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D1
L1
4.7 PH
Cs1
4.7 PF
Bat
C3
4.7 pF
VDD
R3
150k
3
25
26
S/D
27
Cf1
470 pF
5
7
VDD
SW
GND1
V1 = VFB (1 + R1/R2)
FB
Co
100 PF
R1
301k
28
R2
78.7k
GND2
S/D1
BOOT
6
FREQ
10 PH
0.1 PF
18
19
Cb
1.0 PF
9
V1
S/D2
Bypass
GND3
+IN
VO2
12
22
Cs2
4.7 PF
14
8:
20k
Audio In
0.1 PF
Ci
8
-IN
VO1
11
Ri
Rf
200k
Figure 21. Demo Board Reference Schematic
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Demonstration Board Layout
16
Figure 22. Top Trace Layer Silkscreen
Figure 23. Top Layer Silkscreen
Figure 24. Top Trace Layer
Figure 25. Upper Internal GND Layer
Figure 26. Lower Internal VDD Layer
Figure 27. Bottom Trace Layer with GND Plane
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Revision History
Rev
Date
Description
1.0
6/14/05
Under SHUTDOWN (Apps section), changed EN to S/D1 and
(pin– 2) into pin 26, then re-released D/S to the WEB.
C
4/08/13
Changed layout of National Data Sheet to TI format.
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PACKAGE OPTION ADDENDUM
www.ti.com
5-Nov-2017
PACKAGING INFORMATION
Orderable Device
Status
(1)
LM4804LQ/NOPB
LIFEBUY
Package Type Package Pins Package
Drawing
Qty
WQFN
NJB
28
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
TBD
Call TI
Call TI
Op Temp (°C)
Device Marking
(4/5)
L4804LQ
(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)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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