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LM48511
SNAS416K – JULY 2007 – REVISED NOVEMBER 2019
LM48511 3-W, Ultra-Low EMI, Filterless, Mono, Class D Audio Power Amplifier With
Spread Spectrum
•
•
•
•
1
•
•
•
•
•
•
3-W Output into 8 Ω at 5 V With THD+N = 1%
Selectable spread spectrum mode reduces EMI
80% Efficiency
Independent regulator and amplifier shutdown
controls
Dynamically Selectable Regulator Output Voltages
Filterless Class D
3-V to 5.5-V Operation
Low shutdown current
Click and pop suppression
Key specifications
– Quiescent power supply current
– VDD = 3 V 9 mA (Typical)
– VDD = 5 V 13.5 mA (Typical)
– PO at VDD = 5 V, PV1 = 7.8 V, RL = 8 Ω,
THD+N = 1% 3 W (Typical)
– PO at VDD = 3 V, PV1 = 4.8 V, RL = 8 Ω,
THD+N = 1% 1 W (Typical)
– PO at VDD = 5 V, PV1 = 7.8 V, RL = 4 Ω,
THD+N = 1% 5.4 W (Typical)
– Shutdown Current at VDD = 3 V, 0.01 μA
(Typical)
2 Applications
•
•
•
•
•
GPS
Portable media
Cameras
Mobile phones
Handheld games
3 Description
The LM48511 device integrates a boost converter
with a high-efficiency Class D audio power amplifier
to provide 3-W continuous power into an 8-Ω speaker
when operating from a 5-V power supply.
The switching regulator of the LM48511 is a currentmode boost converter operating at a fixed frequency
of 1 MHz. Two selectable feedback networks allow
the LM48511 regulator to dynamically switch between
two different output voltages, improving efficiency by
optimizing the amplifier’s supply voltage based on
battery voltage and output power requirements.
The LM48511 is designed for use in portable devices,
such as GPS, mobile phones, and MP3 players. The
high, 80% efficiency at 5 V, extends battery life when
compared to Boosted Class AB amplifiers.
Independent regulator and amplifier shutdown
controls optimize power savings by disabling the
regulator when high-output power is not required.
The gain of the LM48511 is set by external resistors,
which allows independent gain control from multiple
sources by summing the signals. Output short circuit
and thermal overload protection prevent the device
from damage during fault conditions. Superior click
and pop suppression eliminates audible transients
during power-up and shutdown.
Device Information(1)
PART NUMBER
LM48511
PACKAGE
WQFN (24)
BODY SIZE (NOM)
5.00 mm × 4.00 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
EMI Graph: LM48511 RF Emissions — 3-Inch
Cable
55.0
FCC Class B Limit
50.0
AMPLITUDE (dBPV/m)
1 Features
45.0
40.0
LM45811 EMI Spectrum
35.0
30.0
25.0
20.0
30.0 100.0
200.0
300.0
400.0
500.0
600.0
700.0
800.0
900.0
1000.0
FREQUENCY (MHz)
When operating from a 3-V to 4-V power supply, the
LM48511 can be configured to drive 1 to 2.5 W into
an 8-Ω load with less than 1% distortion (THD+N).
The Class D amplifier features a low-noise PWM
architecture that eliminates the output filter, reducing
external component count, board area consumption,
system cost, and simplifying design. A selectable
spread spectrum modulation scheme suppresses RF
emissions, further reducing the need for output filters.
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM48511
SNAS416K – JULY 2007 – REVISED NOVEMBER 2019
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
4
5
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
5
5
5
5
6
7
8
9
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics VDD = 5 V..........................
Electrical Characteristics VDD = 3.6 V.......................
Electrical Characteristics VDD = 3 V..........................
Typical Characteristics ..............................................
Detailed Description ............................................ 13
7.1 Overview ................................................................. 13
7.2 Functional Block Diagram ....................................... 13
7.3 Feature Description................................................. 14
7.4 Device Functional Modes........................................ 15
8
Application and Implementation ........................ 16
8.1 Application Information............................................ 16
8.2 Typical Application ................................................. 16
9 Power Supply Recommendations...................... 22
10 Layout................................................................... 22
10.1 Layout Guidelines ................................................. 22
10.2 Layout Example .................................................... 22
11 Device and Documentation Support ................. 23
11.1
11.2
11.3
11.4
11.5
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
23
23
23
23
23
12 Mechanical, Packaging, and Orderable
Information ........................................................... 23
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision J (October 2017) to Revision K
•
Page
Changed pin labels in Figure 24 .......................................................................................................................................... 16
Changes from Revision I (August 2017) to Revision J
Page
•
Changed Pin 20 From: FB_GND0 To: FB_GND1 in the Pin Image and Pin Functions table................................................ 4
•
Changed Pin 21 From: FB_GND1 To: FB_GND0 in the Pin Image and Pin Functions table................................................ 4
Changes from Revision H (August 2015) to Revision I
Page
•
Changed Pin 20 From: FB_GND1 To: FB_GND0 in the Pin Image and Pin Functions table................................................ 4
•
Changed Pin 21 From: FB_GND0 To: FB_GND1 in the Pin Image and Pin Functions table................................................ 4
Changes from Revision G (May 2013) to Revision H
•
Added Pin Configuration and Functions section, ESD Ratings table, Feature Description section, Device Functional
Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device
and Documentation Support section, and Mechanical, Packaging, and Orderable Information section .............................. 1
Changes from Revision F (October 2012) to Revision G
•
2
Page
Changed layout of National Data Sheet to TI format ........................................................................................................... 20
Changes from Revision D (February 2012) to Revision E
•
Page
Page
Deleted the Typical limits (Vih and Vil) EC table.................................................................................................................... 6
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SNAS416K – JULY 2007 – REVISED NOVEMBER 2019
Changes from Revision C (November 2007) to Revision D
•
Page
Deleted the “Build of Materials” (BOM) table........................................................................................................................ 20
Changes from Revision B (September 2007) to Revision C
•
Page
Edited the Notes section and added another PO (@VDD = 5 V, RL = 4 Ω) section in the Key Specification division. ............ 1
Changes from Revision A (July 2007) to Revision B
•
Page
Changed the Amplifier Voltage (Operating Ratings section) from 5 V to 4.8 V. .................................................................... 5
Changes from Original (July 2007) to Revision A
•
Page
Input some text edits .............................................................................................................................................................. 1
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LM48511
SNAS416K – JULY 2007 – REVISED NOVEMBER 2019
www.ti.com
5 Pin Configuration and Functions
REGGND
FB_GND0
FB_GND1
24
REGGND
SD_BOOST
NHZ Package
24-Pin WQFN
Top View
23
22
21
20
18 VDD
3
17 VGO-
SOFTSTART
4
16 IN+
SD_AMP
5
15
IN-
SS/FF
6
14
VGO+
GND
7
13 V1
8
9
10
11
12
LS-
2
SW
LSGND
SW
PV1
19 FB
LSGND
1
LS+
FB_SEL
Pin Functions
PIN
NAME
NO.
I/O
DESCRIPTION
DAP
–
—
To be soldered to board for enhanced thermal dissipation. Connect to GND plane.
FB
19
—
Regulator feedback input
Connect FB to an external resistive voltage divider to set the boost output voltage.
FB_GND0
21
—
Ground return for R3, R1 resistor divider
FB_GND1
20
—
Ground return for R3, R2 resistor divider
FB_SEL
1
I
GND
7
—
IN–
15
I
Amplifier inverting input
IN+
16
I
Amplifier noninverting input
LS+
8
O
Amplifier noninverting output
LS–
12
O
Amplifier inverting output
9, 11
—
Amplifier H-Bridge ground
10
—
Amplifier H-Bridge power supply
Connect to V1.
REGGND
22, 23
—
Power ground (booster)
SD_AMP
5
I
Amplifier active-low shutdown
Connect to VDD for normal operation. Connect to GND to disable amplifier.
SD_BOOST
24
I
Regulator active-low shutdown.
Connect to VDD for normal operation. Connect to GND to disable regulator.
SOFT-START
4
—
SS/FF
6
I
2, 3
—
Drain of the internal FET switch
13
—
Amplifier supply voltage
Connect to PV1
VDD
18
—
Power supply
VG0+
14
O
Amplifier noninverting gain output
VG0–
17
O
Amplifier inverting gain output
LSGND
PV1
SW
V1
4
Regulator feedback select
Connect to VDD to select feedback network connected to FB_GND1. Connect to GND to select feedback network
connected to FB_GND0.
Signal ground
Soft-start capacitor
Modulation mode select.
Connect to VDD for spread spectrum mode (SS). Connect to GND for fixed frequency mode (FF).
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1) (2).
MIN
MAX
UNIT
9
V
VDD + 0.3
V
Supply voltage (VDD, PV1, V1)
−0.3
Input voltage
Power dissipation (3)
Internally limited
Junction temperature
150
Storage temperature
−65
(1)
(2)
(3)
°C
150
°C
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur, including inoperability and degradation of
device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or
other conditions beyond those indicated in the Recommended Operating Conditions is not implied. TheRecommended Operating
Conditions indicate conditions at which the device is functional and the device must not be operated beyond such conditions. All
voltages are measured with respect to the ground pin, unless otherwise specified.
If Military/Aerospace specified devices are required, please contact the TI Sales Office/ Distributors for availability and specifications.
The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJJA, and the ambient temperature,
TA. The maximum allowable power dissipation is PDMAX = (TJMAX - TA) / θJA or the number given in Absolute Maximum Ratings,
whichever is lower. For the LM48511, see Figure 20 for additional information.
6.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±2000
Machine model (2)
±200
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
Machine model, applicable std. JESD22-A115-A.
6.3 Recommended Operating Conditions
Temperature range TMIN ≤ TA ≤ TMAX
Supply voltage (VDD)
Amplifier voltage (PV1, V1)
MIN
MAX
−40
85
UNIT
°C
3
5.5
V
4.8
8
V
6.4 Thermal Information
LM48511
THERMAL METRIC (1)
NHZ (WQFN)
UNIT
24 PINS
RθJA
Junction-to-ambient thermal resistance
32.8
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
3.8
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
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SNAS416K – JULY 2007 – REVISED NOVEMBER 2019
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6.5 Electrical Characteristics VDD = 5 V
The following specifications apply for VDD = 5 V, PV1 = 7.8 V (continuos mode), AV = 2 V/V, R3 = 25.5 kΩ, RLS = 4.87 kΩ,
RL = 8 Ω, f = 1 kHz, SS/FF = GND, unless otherwise specified. Limits apply for TA = 25°C. (1)
PARAMETER
TEST CONDITIONS
IDD
Quiescent Power Supply
VIN = 0, RLOAD = ∞
Current
ISD
Shutdown Current (3)
VIH
Logic Voltage Input High
VIL
Logic Voltage Input Low
TWU
Wake-up Time
CSS = 0.1 μF
VOS
Output Offset Voltage
See
PO
Output Power
THD+N
Total Harmonic
Distortion + Noise
Output Noise
εOS
PSRR
Power Supply Rejection
Ratio
(Input Referred)
14.5
22
mA
0.11
1
mA
μA
1.4
V
0.4
49
(4)
0.04
RL = 8 Ω
f = 1 kHz, BW = 22 kHz
THD+N = 1%
FF
RL = 8 Ω
f = 1 kHz, BW = 22 kHz
THD+N = 10%
FF
3.8
SS
3.8
RL = 4 Ω
f = 1 kHz, BW = 22 kHz
THD+N = 1%
FF
5.4
SS
5.4
RL = 4 Ω
f = 1 kHz, BW = 22 kHz
THD+N = 10%
FF
6.7
SS
6.7
PO = 2 W, f = 1 kHz,
RL = 8 Ω
FF
0.03%
SS
0.03%
PO = 3 W, f = 1 kHz,
RL = 4 Ω
FF
0.04%
SS
0.05%
f = 20 Hz to 20 kHz
Inputs to AC GND, No
weighting
FF
32
SS
32
f = 20 Hz to 20 kHz
Inputs to AC GND, A
weighted
FF
22
SS
22
VRIPPLE = 200 mVP-P
Sine,
fRIPPLE = = 217 Hz
FF
88
SS
87
VRIPPLE = 200 mVP-P
Sine,
fRIPPLE = = 1 kHz
FF
88
SS
85
VRIPPLE = 200 mVP-P
Sine,
fRIPPLE = = 10 kHz
FF
77
SS
76
SS
η
Efficiency
f = 1 kHz, RL = 8 Ω, PO = 1 W
VFB
Feedback Pin Reference
Voltage (5)
6
UNIT
Spread Spectrum Mode (SS)
VSD_BOOST = VSD_AMP = SS = FB_SEL = GND
VRIPPLE = 1 VP-P, fRIPPLE = 217 Hz
(3)
(4)
(5)
MAX
13.5
Common-Mode
Rejection Ratio
(Input Referred)
(2)
TYP (2)
Fixed Frequency Mode (FF)
CMRR
(1)
MIN
V
ms
3
mV
3
2.6
3
73
W
W
W
W
µVRMS
µVRMS
dB
dB
dB
dB
80%
1.23
V
RL is a resistive load in series with two inductors to simulate an actual speaker load for RL = 8Ω, the load is 15μH+8Ω+15μH. For
RL = 4 Ω, the load is 15 μH + 4 Ω + 15 μH.
Typical values represent most likely parametric norms at TA = +25ºC, and at the Recommended Operation Conditions at the time of
product characterization and are not specified.
Shutdown current is measured with components R1 and R2 removed.
Offset voltage is determined by: (IDD (with load) — IDD (no load)) x RL.
Feedback pin reference voltage is measured with the Audio Amplifier disconnected from the Boost converter (the Boost converter is
unloaded).
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6.6 Electrical Characteristics VDD = 3.6 V
The following specifications apply for VDD = 3.6 V, PV1 = 7 V (continuous mode), AV = 2 V/V, R3 = 25.5 kΩ, RLS = 5.36 kΩ,
RL = 8 Ω, f = 1 kHz, SS/FF = GND, unless otherwise specified. Limits apply for TA = 25°C. (1)
PARAMETER
TEST CONDITIONS
Quiescent Power Supply
VIN = 0, RLOAD = ∞
Current
IDD
MIN
Fixed Frequency Mode
(FF)
TYP (2)
16
Spread Spectrum Mode
(SS)
mA
0.03
1
μA
VIH
Logic Voltage Input High
1.4
0.96
VIL
Logic Voltage Input Low
0.4
0.84
TWU
Wake-up Time
CSS = 0.1 μF
VOS
Output Offset Voltage
See
PO
Output Power
THD+N
Total Harmonic
Distortion + Noise
Output Noise
εOS
PSRR
Power Supply Rejection
Ratio
(Input Referred)
2.5
RL = 8 Ω, f = 1 kHz,
BW = 22 kHz
THD+N = 10%
FF
3
SS
3
RL = 4 Ω, f = 1 kHz,
BW = 22 kHz
THD+N = 1%
FF
4.3
SS
4.2
RL = 4 Ω, f = 1 kHz,
BW = 22 kHz
THD+N = 10%
FF
5.4
SS
5.3
PO = 1.5 W, f = 1 kHz,
RL = 8 Ω
FF
0.03%
SS
0.03%
PO = 3 W, f = 1 kHz,
RL = 4 Ω
FF
0.04%
SS
0.05%
f = 20 Hz to 20 kHz
Inputs to AC GND, No
weighting
FF
35
SS
36
f = 20 Hz to 20 kHz
Inputs to AC GND, A
weighted
FF
25
SS
26
VRIPPLE = 200 mVP-P
Sine,
fRIPPLE = = 217 Hz
FF
85
SS
86
VRIPPLE = 200 mVP-P
Sine,
fRIPPLE = = 1 kHz
FF
87
SS
86
VRIPPLE = 200 mVP-P
Sine,
fRIPPLE = = 10 kHz
FF
78
SS
77
Efficiency
f = 1 kHz, RL = 8 Ω, PO = 1 W
VFB
Feedback Pin Reference
Voltage (5)
(2)
(3)
(4)
(5)
mV
SS
η
(1)
0.04
2.5
VRIPPLE = 1 VP-P, fRIPPLE = 217 Hz
V
ms
FF
Common-Mode
Rejection Ratio
(Input Referred)
V
50
RL = 8 Ω, f = 1 kHz,
BW = 22 kHz
THD+N = 1%
CMRR
mA
26.6
Shutdown Current (3)
VSD_BOOST = VSD_AMP = SS = FB_SEL = GND
UNIT
17.5
ISD
(4)
MAX
73
W
W
W
W
µVRMS
µVRMS
dB
dB
dB
dB
77%
1.23
V
RL is a resistive load in series with two inductors to simulate an actual speaker load for RL = 8Ω, the load is 15μH+8Ω+15μH. For
RL = 4 Ω, the load is 15 μH + 4 Ω + 15 μH.
Typical values represent most likely parametric norms at TA = +25ºC, and at the Recommended Operation Conditions at the time of
product characterization and are not specified.
Shutdown current is measured with components R1 and R2 removed.
Offset voltage is determined by: (IDD (with load) — IDD (no load)) x RL.
Feedback pin reference voltage is measured with the Audio Amplifier disconnected from the Boost converter (the Boost converter is
unloaded).
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6.7 Electrical Characteristics VDD = 3 V
The following specifications apply for VDD = 3 V, PV1 = 4.8 V (continuos mode), AV = 2V/V, R3 = 25.5 kΩ, RLS = 9.31 kΩ,
RL = 8 Ω, f = 1 kHz, SS/FF = GND, unless otherwise specified. Limits apply for TA = 25°C. (1)
PARAMETER
TEST CONDITIONS
MIN
Fixed Frequency Mode (FF)
TYP (2)
MAX
9
UNIT
mA
IDD
Quiescent Power Supply
VIN = 0, RLOAD = ∞
Current
ISD
Shutdown Current (3)
VIH
Logic Voltage Input High
0.91
V
VIL
Logic Voltage Input Low
0.79
V
TWU
Wake-up Time
VOS
Output Offset Voltage (4)
PO
Output Power
THD+N
Total Harmonic
Distortion + Noise
Output Noise
εOS
PSRR
Power Supply Rejection
Ratio
(Input Referred)
Spread Spectrum Mode (SS)
FF
1.3
SS
1.3
RL = 4 Ω, f = 1 kHz,
BW = 22 kHz
THD+N = 1%
FF
1.8
SS
1.8
RL = 4 Ω, f = 1 kHz,
BW = 22 kHz
THD+N = 10%
FF
2.2
SS
2.2
PO = 500 mW, f = 1 kHz, FF
RL = 8 Ω
SS
0.02%
PO = 500 mW, f = 1 kHz, FF
RL = 4 Ω
SS
0.04%
0.84
1
SS
35
f = 20 Hz to 20 kHz
Inputs to AC GND, A
weighted
FF
25
SS
25
VRIPPLE = 200 mVP-P
Sine,
fRIPPLE = = 217 Hz
FF
89
SS
89
VRIPPLE = 200 mVP-P
Sine,
fRIPPLE = = 1 kHz
FF
88
SS
88
VRIPPLE = 200 mVP-P
Sine,
fRIPPLE = = 10 kHz
FF
78
SS
78
f = 1 kHz, RL = 8 Ω, PO = 1 W
VFB
W
W
W
0.06%
35
Feedback Pin Reference
Voltage (5)
W
0.03%
FF
Efficiency
8
1
f = 20Hz to 20kHz
Inputs to AC GND, No
weighting
η
(3)
(4)
(5)
ms
mV
RL = 8 Ω, f = 1 kHz,
BW = 22 kHz
THD+N = 10%
VRIPPLE = 1 VP-P, fRIPPLE = 217 Hz
μA
49
FF
SS
mA
1
0.04
RL = 8 Ω, f = 1 kHz,
BW = 22 kHz
THD+N = 1%
Common-Mode
Rejection Ratio
(Input Referred)
(2)
0.01
CSS = 0.1μF
CMRR
(1)
9.5
VSD_BOOST = VSD_AMP = SS = FB_SEL = GND
71
µVRMS
µVRMS
dB
dB
dB
dB
75%
1.23
V
RL is a resistive load in series with two inductors to simulate an actual speaker load for RL = 8Ω, the load is 15μH+8Ω+15μH. For
RL = 4 Ω, the load is 15 μH + 4 Ω + 15 μH.
Typical values represent most likely parametric norms at TA = +25ºC, and at the Recommended Operation Conditions at the time of
product characterization and are not specified.
Shutdown current is measured with components R1 and R2 removed.
Offset voltage is determined by: (IDD (with load) — IDD (no load)) x RL.
Feedback pin reference voltage is measured with the Audio Amplifier disconnected from the Boost converter (the Boost converter is
unloaded).
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10
10
1
1
FIXED FREQUENCY
FIXED FREQUENCY
THD+N (%)
THD+N (%)
6.8 Typical Characteristics
0.1
0.1
0.01
0.01
SPREAD SPECTRUM
SPREAD SPECTRUM
0.001
20
200
2k
20k
0.001
20
FREQUENCY (Hz)
Figure 1. THD+N vs Frequency
VDD = 5 V, RL = 8 Ω
PO = 2 W, Filter = 22 kHz, PV1 = 7.8 V
2k
20k
Figure 2. THD+N vs Frequency
VDD = 3.6 V, RL = 8 Ω
PO = 500 mW, Filter = 22 kHz, PV1 = 4.8 V
10
10
SPREAD SPECTRUM,
CIN = 180 nF
1
1
FIXED FREQUENCY,
CIN = 180 nF
THD+N (%)
THD+N (%)
200
FREQUENCY (Hz)
0.1
SPREAD SPECTRUM
0.1
0.01
SPREAD SPECTRUM, CIN = 1 PF
FIXED FREQUENCY, CIN = 1 PF
0.001
20
200
2k
0.01
10m
20k
100m
1
5
OUTPUT POWER (W)
FREQUENCY (Hz)
Figure 3. THD+N vs Frequency
VDD = 3 V, RL = 8 Ω
PO = 1.5 W, Filter = 22 kHz, PV1 = 7 V
Figure 4. THD+N vs Output Power
VDD = 5 V, RL = 8 Ω
PO = 1.5 W, f = 1 kHz, Filter = 22 kHz, PV1 = 7.8 V
10
10
1
THD+N (%)
FIXED FREQUENCY
1
THD+N (%)
FIXED FREQUENCY
SPREAD SPECTRUM
0.1
FIXED FREQUENCY
SPREAD SPECTRUM
0.1
0.01
10m
100m
1
5
0.01
10m
OUTPUT POWER (W)
100m
1
5
OUTPUT POWER (W)
Figure 5. THD+N vs Output Power
VDD = 3.6 V, RL = 8 Ω
f = 1 kHz, Filter = 22 kHz, PV1 = 7 V
Figure 6. THD+N vs Output Power
VDD = 3 V, RL = 8 Ω
f = 1 kHz, Filter = 22 kHz, PV1 = 4.8 V
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Typical Characteristics (continued)
10
10
3V
9.31 k:
THD+N (%)
1
THD+N (%)
1
3.6V
5.35 k:
0.1
4.87 k:
0.1
5V
0.01
10m
100m
1
0.01
10m
5
100m
OUTPUT POWER (W)
Figure 8. THD+N vs Output Power
VDD = 3.6 V, RL = 8 Ω
Filter = 22 kHz, PV1 = 7.8 V, PV1 = 7 V, PV1 = 4.8 V, FF
100
100
90
90
80
80
70
70
EFFICIENCY (%)
EFFICIENCY (%)
5
OUTPUT POWER (W)
Figure 7. THD+N vs Output Power
VDD = 3 V, 3.6 V, 5 V, RL = 8 Ω
f = 1kHz, Filter = 22 kHz, R1 = 4.87 kΩ, FF
60
50
40
30
60
50
40
30
20
20
10
10
0
1
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
4.0
0
0.5
1.0
1.5
2.0
2.5
3.0
OUTPUT POWER (W)
OUTPUT POWER (W)
Figure 9. Boost Amplifier vs Output Power
VDD = 5 V, RL = 8 Ω
f = 1 kHz, PV1 = 7.8 V
Figure 10. Boost Amplifier vs Output Power
VDD = 3.6 V, RL = 8 Ω
f = 1 kHz, PV1 = 7 V
0
100
90
-20
70
PSRR (dB)
EFFICIENCY (%)
80
60
50
40
-40
FIXED FREQUENCY
-60
SPREAD SPECTRUM
30
-80
20
10
0
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
-100
20
2k
20k
FREQUENCY (Hz)
OUTPUT POWER (W)
Figure 11. Boost Amplifier vs Output Power
VDD = 3 V, RL = 8 Ω
f = 1 kHz, PV1 = 4.8 V
10
200
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Figure 12. PSRR vs Frequency
VDD = 5 V, RL = 8 Ω
VRIPPLE = 200 mVPP, PV1 = 7.8 V
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0
0
-20
-20
-40
-60
PSRR (dB)
PSRR (dB)
Typical Characteristics (continued)
FIXED FREQUENCY
SPREAD SPECTRUM
-40
-60
SPREAD SPECTRUM
-80
-80
-100
20
200
2k
FIXED FREQUENCY
-100
20
20k
200
2k
20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 13. PSRR vs Frequency
VDD = 3.6 V, RL = 8 Ω
VRIPPLE = 200 mVPP, PV1 = 7 V
Figure 14. PSRR vs Frequency
VDD = 3 V, RL = 8 Ω
VRIPPLE = 200 mVPP, PV1 = 4.8 V
30
23
SPREAD SPECTRUM
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
21
25
20
15
FIXED FREQUENCY
10
SPREAD SPECTRUM
19
17
15
13
11
FIXED FREQUENCY
9
7
5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
5
2.5
6.0
3.5
4.0
4.5
5.0
5.5
6.0
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
Figure 15. Supply Current vs Supply Voltage
PV1 = 7.8 V
Figure 16. Supply Current vs Supply Voltage
PV1 = 7 V
11
1.8
1.6
POWER DISSIPATION (W)
10
SUPPLY CURRENT (mA)
3.0
SPREAD
SPECTRUM
9
8
7
6
3.0
3.5
4.0
4.5
1.2
1.0
0.8
0.6
0.4
0.2
FIXED FREQUENCY
5
2.5
1.4
5.0
5.5
0
6.0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
OUTPUT POWER (W)
SUPPLY VOLTAGE (V)
Figure 17. Supply Current vs Supply Voltage
PV1 = 4.8 V
Figure 18. Power Dissipation vs Output Power
VDD = 5 V, RL = 8 Ω
PV1 = 7.8 V, FF
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Typical Characteristics (continued)
1.8
0.5
0.4
POWER DISSIPATION (W)
POWER DISSIPATION (W)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.3
0.2
0.1
0.2
0
0
0.5
1.0
1.5
2.0
2.5
3.0
0
3.5
0
0.2
OUTPUT POWER (W)
0.6
0.8
1.0
1.2
1.4
1.6
OUTPUT POWER (W)
Figure 19. Power Dissipation vs Output Power
VDD = 3.6 V, RL = 8 Ω
PV1 = 7 V, FF
Figure 20. Power Dissipation vs Output Power
VDD = 3 V, RL = 8 Ω
PV1 = 4.8 V, FF
100
100
90
90
80
80
70
70
EFFICIENCY (%)
EFFICIENCY (%)
0.4
60
50
40
30
60
50
40
30
20
20
10
10
0
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.1
0
LOAD CURRENT (A)
0.2
0.3
0.4
0.5
0.6
LOAD CURRENT (A)
Figure 21. Boost Converter Efficiency vs ILOAD(DC)
VDD = 5 V, PV1 = 7.8 V
Figure 22. Boost Converter Efficiency vs ILOAD(DC)
VDD = 3.6 V, PV1 = 7 V
100
90
EFFICIENCY (%)
80
70
60
50
40
30
20
10
0
0
0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.4
LOAD CURRENT (A)
Figure 23. Boost Converter Efficiency vs ILOAD(DC)
VDD = 3 V, PV1 = 4.8 V
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7 Detailed Description
7.1 Overview
The LM48511 integrates a boost converter with a high-efficiency Class D audio power amplifier, which features a
low-noise PWM architecture that eliminates the output filter, reducing external component count, board area
consumption, system cost, and simplifying design. A selectable spread spectrum modulation scheme suppresses
RF emissions, further reducing the need for output filters. Two selectable feedback networks allow the LM48511
regulator to dynamically switch between two different output voltages, improving efficiency by optimizing the
amplifier’s supply voltage based on battery voltage and output power requirements. The gain of the LM48511 is
set by external resistors, which allows independent gain control from multiple sources by summing the signals.
Output short circuit and thermal overload protection prevent the device from damage during fault conditions.
7.2 Functional Block Diagram
+3.0V to +5.5V
L1
6.8 PH
CS1
10 PF
VDD
D1
C2
100 PF
SW
C1
280 pF
R3
25.5 k:
SD_BOOST
REGGND
R4
2.5 k:
MODULATOR
FB
SOFTSTART
R2
9.31 k:
CSS
0.1 PF
R1
4.87 k:
FB_GND1
OSCILLATOR
FB_SEL
FB_GND0
V1
SD_AMP
PV1
C4
1 PF
VGOCIN
VIN
+
R5
20 k:
R6
20 k:
IN+
R7
20 k:
LS+
MODULATOR
H-BRIDGE
IN-
VINCIN
C3
1 PF
R8
20 k:
LS-
VGO+
OSCILLATOR
SS/FF
GND
LSGND
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7.3 Feature Description
7.3.1 General Amplifier Function
The LM48511 features a Class D audio power amplifier that uses a filterless modulation scheme, reducing
external component count, conserving board space and reducing system cost. The outputs of the device
transition from PV1 to GND with a 300-kHz switching frequency. With no signal applied, the outputs (VLS+ and
VLS-) switch with a 50% duty cycle, in phase, causing the two outputs to cancel. This cancellation results in no
net voltage across the speaker, thus there is no current to the load in the idle state.
With the input signal applied, the duty cycle (pulse width) of the LM48511 outputs changes. For increasing output
voltage, the duty cycle of VLS+ increases, while the duty cycle of VLS-decreases. For decreasing output voltages,
the converse occurs. The difference between the two pulse widths yields the differential output voltage.
7.3.2 Differential Amplifier Explanation
The LM48511 includes fully differential amplifier that features differential input and output stages. A differential
amplifier amplifies the difference between the two input signals. Traditional audio power amplifiers have typically
offered only single-ended inputs resulting in a 6dB reduction in signal to noise ratio relative to differential inputs.
The LM48511 also offers the possibility of DC input coupling which eliminates the two external AC coupling, DC
blocking capacitors. The LM48511 can be used, however, as a single-ended input amplifier while still retaining
the fully differential benefits of the device. In fact, completely unrelated signals may be placed on the input pins.
The LM48511 simply amplifies the difference between the signals. A major benefit of a differential amplifier is the
improved common-mode rejection ratio (CMRR) over single input amplifiers. The common-mode rejection
characteristic of the differential amplifier reduces sensitivity to ground offset related noise injection, especially
important in high noise applications.
7.3.3 Audio Amplifier Power Dissipation and Efficiency
The major benefit of a Class D amplifier is increased efficiency versus a Class AB. The efficiency of the
LM48511 is attributed to the region of operation of the transistors in the output stage. The Class D output stage
acts as current steering switches, consuming negligible amounts of power compared to their Class AB
counterparts. Most of the power loss associated with the output stage is due to the IR loss of the MOSFET ONresistance, along with switching losses due to gate charge.
7.3.4 Regulator 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 LM48511 FET switch. The switch power dissipation from ON-time
conduction is calculated by:
PD(SWITCH) = DC × (IINDUCTOR(AVE))2 × RDS(ON) (W)
where
•
DC is the duty cycle.
(1)
7.3.5 Shutdown Function
The LM48511 features independent amplifier and regulator shutdown controls, allowing each portion of the
device to be disabled or enabled independently. SD_AMP controls the Class D amplifiers, while SD_BOOST
controls the regulator. Driving either inputs low disables the corresponding portion of the device, and reducing
supply current.
When the regulator is disabled, both FB_GND switches open, further reducing shutdown current by eliminating
the current path to GND through the regulator feedback network. Without the GND switches, the feedback
resistors as shown in the Functional Block Diagram would consume an additional 165 μA from a 5-V supply. With
the regulator disabled, there is still a current path from VDD, through the inductor and diode, to the amplifier
power supply. This allows the amplifier to operate even when the regulator is disabled. The voltage at PV1 and
V1 will be:
(VDD – [VD + (IL x DCR)]
Where
•
•
14
VD is the forward voltage of the Schottky diode
VD is the forward voltage of the Schottky diode
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Feature Description (continued)
•
•
IL is the current through the inductor
DCR is the DC resistance of the inductor
(2)
Additionally, when the regulator is disabled, an external voltage from 5 V to 8 V can be applied directly to PV1
and V1 to power the amplifier.
It is best to switch between ground and VDD for minimum current consumption while in shutdown. The LM48511
may be disabled with shutdown voltages in between GND and VDD, the idle current will be greater than the
typical 0.1-µA value. Increased THD+N may also be observed when a voltage of less than VDD is applied to
SD_AMP .
7.3.6 Regulator Feedback Select
The LM45811 regulator features two feedback paths as shown in the Functional Block Diagram, which allow the
regulator to easily switch between two different output voltages. The voltage divider consists of the high side
resistor, R3, and the low side resistors (RLS), R1 and R2. R3 is connected to the output of the boost regulator,
the mid-point of each divider is connected to FB, and the low side resistors are connected to either FB_GND1 or
FB_GND0. FB_SEL determines which FB_GND switch is closed, which in turn determines which feedback path
is used. For example if FB_SEL = VDD, the FB_GND1 switch is closed, while the FB_GND0 switch remains open,
creating a current path through the resistors connected to FB_GND1. Conversely, if FB_SEL = GND, the
FB_GND0 switch is closed, while the FB_GND1 switch remains open, creating a current path through the
resistors connected to FB_GND0.
FB_SEL can be susceptible to noise interference. To prevent an accidental state change, either bypass FB_SEL
with a 0.1µF capacitor to GND, or connect the higher voltage feedback network to FB_GND0, and the lower
voltage feedback network to FB_GND1. Because the higher output voltage configuration typically generates
more noise on VDD, this configuration minimizes the VDD noise exposure of FB_SEL, as FB_SEL = GND for
FB_GND0 (high voltage output) and FB_SEL = VDD for FB_GND1 (low voltage output).
The selectable feedback networks maximize efficiency in two ways. In applications where the system power
supply voltage changes, such as a mobile GPS receiver, that transitions from battery power, to AC line, to a car
power adapter, the LM48511 can be configured to generate a lower voltage when the system power supply
voltages is lower, and conversely, generate a higher voltage when the system power supply is higher. See the
Setting the Regulator Output Voltage (PV1) section.
In applications where the same speaker/amplifier combination is used for different purposes with different audio
power requirements, such as a cell phone ear piece/speaker phone speaker, the ability to quickly switch between
two different voltages allows for optimization of the amplifier power supply, increasing overall system efficiency.
When audio power demands are low (ear piece mode) the regulator output voltage can be set lower, reducing
quiescent current consumption. When audio power demands increase (speaker phone mode), a higher voltage
increases the amplifier headroom, increasing the audio power delivered to the speaker.
7.4 Device Functional Modes
The LM48511 features two modulations schemes, a fixed frequency mode (FF) and a spread spectrum mode
(SS).
7.4.1 7.4.1 Fixed Frequency
Select the fixed frequency mode by setting SS/FF = GND. In fixed frequency mode, the amplifier outputs switch
at a constant 300 kHz. In fixed frequency mode, the output spectrum consists of the fundamental and its
associated harmonics (see Typical Characteristics).
7.4.2 7.4.2 Spread Spectrum Mode
Set SS/FF = VDD for spread spectrum mode. The logic selectable spread spectrum mode eliminates the need
for output filters, ferrite beads or chokes. In spread spectrum mode, the switching frequency varies randomly by
10% about a 330-kHz center frequency, reducing the wideband spectral contend, improving EMI emissions
radiated by the speaker and associated cables and traces. Where a fixed frequency class D exhibits large
amounts of spectral energy at multiples of the switching frequency, the spread spectrum architecture of the
LM48511 spreads that energy over a larger bandwidth (see Typical Characteristics). The cycle-to-cycle variation
of the switching period does not affect the audio reproduction, efficiency, or PSRR.
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LM48511 integrates a boost converter with a high-efficiency Class D audio power amplifier, which uses a
filterless modulation scheme, reducing external component count, board area consumption and system cost. The
major benefit of a Class D amplifier is increased efficiency versus a Class AB. The LM48511 regulator has two
selectable feedback paths, which allow the regulator to dynamically switch between two different output voltages
easily. In addition, the LM48511 regulator features two different switching modes, improving light load efficiency
by minimizing losses due to MOSFET gate charge. The amplifier gain of the LM48511 is set by four external
resistors. Careful matching of those resistor pairs is required for optimum performance.
8.2 Typical Application
VDD
20
1
VDD
24
5
17
GND2
Audio Input
1
1
GND2
2
2
3
3
4
GND2
4
CIN+
R5
20k
CIN-
R7
180 nF
20k
16
15
14
GND1
GND
GND2
GND3
3
GND1
3
GND2
C4
1 PF
22
GND3
23
FB_GND0
FB_GND1
FB_SEL
V1
LM48511SQ
/SD_Boost
PV1
13
10
/SD_Amp
VGO-
LS+
8
Speaker
2
IN+
INVGO+
VDD
SS_EN
2
2
GND3
R8
20k
1
GND3
FB
6
180 nF
R6
20k
Softstart
GND2
4
19
21
GND2
GND3
SW
+
R2
9.31k 100 nF
GND2
C3
1 PF
LS-
12
1
7
R1
4.87k
100 PF
SW
CSoftstart
GND2
FB_SEL VDD
1
1
2
2
3
3
GND2
+C2
GND1
SD_Amp
1
1
2
2
3
3
GND3
1 PF
CS3
9
SD_Boost
1
1
2
2
3
3
VDD
GND3
1 PF
CS2
D1
6.8 PH
18
GND1 (Class D GND)
GND2 (AGND)
GND3 (Switch GND)
L1
VDD
+
10 PF
CS1
VDD
GND2
GND1
+ C1
280 pF
R3
25.5k
R4
2.5k
11
1
2
SS-EN
VDD
GND1 GND1 GND2
1
2
3
GND2
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Figure 24. Typical LM48511 Audio Amplifier Application Circuit
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Typical Application (continued)
8.2.1 Design Requirements
Table 1 lists the design parameters for this example.
Table 1. Design Parameters
PARAMETERS
VALUES
Supply voltage range
3.0 V to 5.5 V
Amplifier range
4.8 V to 8 V
Temperature range
–40°C to 85°C
8.2.2 Detailed Design Procedure
8.2.2.1 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
LM48511 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 must 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 and Murata.
8.2.2.2 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 PV1, V1 and VDD pins must be as close to the device as possible.
8.2.2.3 Audio Amplifier Gain Setting Resistor Selection
The amplifier gain of the LM48511 is set by four external resistors, the input resistors, R5 and R7, and the feed
back resistors R6 and R8.. The amplifier gain is given by:
Where RIN is the input resistor and RF is the feedback resistor.
AVD = 2 × RF / RIN
(3)
Careful matching of the resistor pairs, R6 and R8, and R5 and R7, is required for optimum performance. Any
mismatch between the resistors results in a differential gain error that leads to an increase in THD+N, decrease
in PSRR and CMRR, as well as an increase in output offset voltage. Resistors with a tolerance of 1% or better
are recommended.
The gain setting resistors must be placed as close to the device as possible. Keeping the input traces close
together and of the same length increases noise rejection in noisy environments. Noise coupled onto the input
traces which are physically close to each other will be common mode and easily rejected.
8.2.2.4 Audio Amplifier Input Capacitor Selection
Input capacitors may be required for some applications, or when the audio source is single-ended. Input
capacitors block the DC component of the audio signal, eliminating any conflict between the DC component of
the audio source and the bias voltage of the LM48511. The input capacitors create a highpass filter with the input
resistors RIN. The -3dB point of the highpass filter is found by:
f = 1 / 2πRINCIN
(4)
In single-ended configurations, the input capacitor value affects click-and-pop performance. The LM48511
features a 50-mg turnon delaly. Choose the input capacitor / input resistor values such that the capacitor is
charged before the 50-ms turnon delay expires. A capacitor value of 0.18 μF and a 20-kΩ input resistor are
recommended. In differential applications, the charging of the input capacitor does not affect click-and-pop
significantly.
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The input capacitors can also be used to remove low-frequency content from the audio signal. Highpass filtering
the audio signal helps protect speakers that can not reproduce or may be damaged by low frequencies. When
the LM48511 is using a single-ended source, power supply noise on the ground is seen as an input signal.
Setting the highpass filter point above the power supply noise frequencies, 217 Hz in a GSM phone, for example,
filters out the noise such that it is not amplified and heard on the output. Capacitors with a tolerance of 10% or
better are recommended for impedance matching and improved CMRR and PSRR.
8.2.2.5 Selecting Regulator Output Capacitor
A single 100-µF low ESR tantalum capacitor provides sufficient output capacitance for most applications. Higher
capacitor values improve line regulation and transient response. Typical electrolytic capacitors are not suitable
for switching converters that operate above 500 kHz because of significant ringing and temperature rise due to
self-heating from ripple current. An output capacitor with excessive ESR reduces phase margin and causes
instability.
8.2.2.6 Selecting Regulating Bypass Capacitor
A supply bypass 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 capacitors are the best
choice. A nominal value of 10 μF is recommended, but larger values can be used. Because 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.
8.2.2.7 Selecting the Soft-Start (CSS) Capacitor
The soft-start function charges the boost converter reference voltage slowly. This allows the output of the boost
converter to ramp up slowly thus limiting the transient current at start-up. Selecting a soft-start capacitor (CSS)
value presents a trade off between the wake-up time and the start-up transient current. Using a larger capacitor
value will increase wake-up time and decrease start-up transient current while the apposite effect happens with a
smaller capacitor value. A general guideline is to use a capacitor value 1000 times smaller than the output
capacitance of the boost converter (C2). A 0.1-uF soft-start capacitor is recommended for a typical application.
Table 2 shows the relationship between CSS start-up time and surge current.
Table 2. Soft-Start Capacitor Start-Up Time and Surge Current
CSS
(μF)
(1)
(1)
BOOST SET-UP TIME
(ms)
INPUT SURGE CURRENT
(mA)
0.1
5.1
330
0.22
10.5
255
0.47
21.7
220
VDD = 5 V, PV1 = 7.8 V (continuous mode)
8.2.2.8 Selecting Diode (D1)
Use a Schottkey diode, as shown in Figure 24. A 30-V diode such as the DFLS230LH from Diodes Incorporated
is recommended. The DFLS230LH diodes are designed to handle a maximum average current of 2 A.
8.2.2.9 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 by:
Duty Cycle = (PV1 + VD – VDD) / (PV1 + VD – VSW)
(5)
This applies for continuous mode operation.
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8.2.2.10 Selecting Inductor Value
Inductor value involves trade-offs in performance. Larger inductors reduce 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 × (IP)2
Where
•
IP is the peak inductor current
(6)
The LM48511 will limit its switch current based on peak current. With IP 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. Boost converters shift over to discontinuous operation if the load is reduced far enough, but a larger
inductor stays continuous over a wider load current range.
8.2.2.11 Inductor Supplies
The recommended inductor for the LM48511 is the IHLP-2525CZ-01 from Vishay Dale. When selecting an
inductor, the continuous current rating must be high enough to avoid saturation at peak currents. A suitable core
type must be used to minimize switching losses, and DCR losses must be considered when selecting the current
rating. Use shielded inductors in systems that are susceptible to RF interference.
8.2.2.12 Setting the Regulator Output Voltage (PV1)
The output voltage of the regulator is set through one of two external resistive voltage-dividers (R3 in
combination with either R1 or R2) connected to FB (Figure 24). The resistor, R4 is only for compensation
purposes and does not affect the regulator output voltage. The regulator output voltage is set by the following
equation:
PV1 = VFB [1 + R3 / RLS]
Where
•
VFB is 1.23 V, and RLS is the low side resistor (R1 or R2)
(7)
To simplify resistor selection:
RLS = (R3VFB) / (PV1 – VFB)
(8)
A value of approximately 25.5 kΩ is recommended for R3.
The quiescent current of the boost regulator is directly related to the difference between its input and output
voltages, the larger the difference, the higher the quiescent current. For improved power consumption the
following regulator input/output voltage combinations are recommended:
Table 3. Recommended Regulator Input and Output Voltages
(1)
(1)
VDD (V)
PV1 (V)
R3 (kΩ)
RLS (kΩ)
3.0
4.8
25.5
9.31
POUT into 8 Ω (W)
1
3.6
7.1
25.5
5.35
2.5
5
7.8
25.5
4.87
3
The values of PV1 are for continuous mode operation.
For feedback path selection, see Regulator Feedback Select.
8.2.2.13 Discontinuous and Continuous Operation
The LM48511 regulator features two different switching modes. Under light-load conditions, the regulator
operates in a variable frequency, discontinuous, pulse-skipping mode, that improves light load efficiency by
minimizing losses due to MOSFET gate charge. Under heavy loads, the LM48511 regulator automatically
switches to a continuous, fixed-frequency PWM mode, improving load regulation. In discontinuous mode, the
regulator output voltage is typically 400 mV higher than the expected (calculated) voltage in continuous mode.
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8.2.2.14 ISW Feed-Forward Compensation for Boost Converter
Although the LM48511 regulator is internally compensated, an external feed-forward capacitor, (C1) may be
required for stability. The compensation capacitor places a zero in regulator loop response. The recommended
frequency of the zero (fZ) is 22.2 kHz. The value of C1 is given by:
C1 = 1 / 2πR3fZ
(9)
In addition to C1, a compensation resistor, R4 is required to cancel the zero contributed by the ESR of the
regulator output capacitor. Calculate the zero frequency of the output capacitor by:
fCO = 1 / 2πRCOCO
where
•
R CO is the ESR of the output capacitor
(10)
The value of RFB3 is given by:
R4 = 1 / 2πfCOC1
(11)
8.2.2.15 Calculating Regulator Output Current
The load current of the boost converter is related to the average inductor current by the relation:
IAMP = IINDUCTOR(AVE) × (1 – DC) (A)
where
•
DC is the duty cycle of the application
(12)
The switch current can be found by:
ISW = IINDUCTOR(AVE) + 1/2 (IRIPPLE) (A)
(13)
Inductor ripple current is dependent on inductance, duty cycle, supply voltage and frequency:
IRIPPLE = DC × (VDD – VSW) / (f × L) (A)
where
•
f = switching frequency = 1MHz
(14)
combining all terms, we can develop an expression which allows the maximum available load current to be
calculated:
IAMP(max) = (1–DC) × [ISW(max)– DC (V – VSW)] / 2fL (A)
(15)
The equation shown to calculate maximum load current takes into account the losses in the inductor or turnoff
switching losses of the FET and diode.
8.2.2.16 Design Parameters VSW and ISW
The value of the FET "ON" voltage (referred to as VSW in Equation 9 thru Equation 12) is dependent on load
current. A good approximation can be obtained by multiplying the ON-resistance (RDS(ON) of the FET times the
average inductor current. The maximum peak switch current the device can deliver is dependent on duty cycle.
20
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8.2.3 Application Curve
POUT (W) IDD (A) K (%)
100
10
1
POUT (W)
THD+N (%)
IDD (A)
K (%)
0.1
3
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4
4.1
VDD (V)
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5
D001
Figure 25. VDD vs POUT, IDD, and Efficiency With 4-Ω Load
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9 Power Supply Recommendations
The devices are designed to operate from an input supply voltage (VDD) operating range from 3 V to 5.5 V, but
the absolute maximum rating is 9 V.
As with any amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection. The capacitor location on both PV1, V1 and VDD pins must be as close to the device as possible.
10 Layout
10.1 Layout Guidelines
This section provides general practical guidelines for PCB layouts that use various power and ground traces.
Designers must note that these are only rule-of-thumb recommendations and the actual results are predicated on
the final layout.
10.1.1 Power and Ground Circuits
Star trace routing techniques can have a major positive impact on low-level signal performance. Star trace
routing refers to using individual traces that radiate from a signal point to feed power and ground to each circuit
or even device.
10.1.2 Layout Helpful Hints
• Avoid routing traces under the inductor.
• Use three separate grounds that eventually connect to one point:
– Signal or quiet ground (GND)
– Ground for the LM48511 device (LSGND)
– SW (REGGND) (switch ground). This trace for the switch ground carries the heaviest current (3 A) and
therefore is the nosiest. Make this trace as wide and short as possible and keep at a distance from the
quiet ground and device ground. Give distance priority to the quiet ground.
10.2 Layout Example
Figure 26. Layout Example
22
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11 Device and Documentation Support
11.1 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
11.2 Community Resources
TI E2E™ support forums are an engineer's go-to source for fast, verified answers and design help — straight
from the experts. Search existing answers or ask your own question to get the quick design help you need.
Linked content is provided "AS IS" by the respective contributors. They do not constitute TI specifications and do
not necessarily reflect TI's views; see TI's Terms of Use.
11.3 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.4 Electrostatic Discharge Caution
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.
11.5 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM48511SQ/NOPB
ACTIVE
WQFN
NHZ
24
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
48511SQ
LM48511SQX/NOPB
ACTIVE
WQFN
NHZ
24
4500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
48511SQ
(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
