LME49610TS [NSC]
High Performance, High Fidelity, High Current Audio Buffer; 高性能，高保真，高电流音频缓冲器
| 型号： | LME49610TS |
| 厂家： | 
National Semiconductor |
| 描述： | High Performance, High Fidelity, High Current Audio Buffer |
| 文件： | 总18页 (文件大小：457K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
October 28, 2009
LME49610ꢀ
High Performance, High Fidelity, High Current Audio Buffer
General Description
Key Specifications
The LME49610 is a high performance, low distortion high fi-
delity 250mA audio buffer. The LME49610 is designed for a
wide range of applications. When used inside the feedback
loop of an op amp, it increases output current, improves ca-
pacitive load drive, and eliminates thermal feedback.
■ꢀLow THD+N
(VOUT = 3VRMS, f = 1kHz, Fig. 2)
0.00003% (typ)
2000V/μs (typ)
250mA (typ)
■ꢀSlew Rate
■ꢀHigh Output Current
■ꢀBandwidth
The LME49610 offers a pin-selectable bandwidth: a low cur-
rent, 120MHz bandwidth mode that consumes 13mA and a
wide 200MHz bandwidth mode that consumes 19mA. In both
modes the LME49610 has a nominal 2000V/μs slew rate.
Bandwidth is easily adjusted by either leaving the BW pin un-
connected, connecting it to the VEE pin or connecting a resis-
tor between the BW pin and the VEE pin.
BW pin floating
120MHz (typ)
200MHz (typ)
BW connected to VEE
■ꢀSupply Voltage Range
±2.25V ≤VDD ≤±22V
The LME49610 is fully protected through internal current limit
and thermal shutdown.
Features
Pin-selectable bandwidth and quiescent current
Pure fidelity. Pure performance
Short circuit protection
■
■
■
■
■
Thermal shutdown
TO–263 surface-mount package
Applications
Headphone amplifier output drive stage
■
■
■
■
■
■
Line drivers
Low power audio amplifiers
High-current operational amplifier output stage
ATE pin driver buffer
Power supply regulator
Functional Block Diagram
30042541
FIGURE 1. Functional Block Diagram
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2009 National Semiconductor Corporation
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Connection Diagrams
TO-263 Package (Note 9)
30042539
Top View
Order Number LME49610TS
See NS Package Number TS5B
30042542
Top View
U — Wafer fabrication code
Z — Assembly plant
XY — 2 Digit date code
TT — Lot traceability
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2
4°C/W
65°C/W
20°C/W
ꢁθJC
ꢁθJA
Absolute Maximum Ratings (Note 1, Note
2)
ꢁθJA (Note 3)
Soldering Information
TO–263 Package (10 seconds)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
260°C
Supply Voltage
46V
2000V
200V
Operating Ratings (Note 1, Note 2)
ESD Rating (Note 4)
ESD Rating (Note 5)
Storage Temperature
Junction Temperature
Thermal Resistance
Temperature Range
TMIN ≤ TA ≤ TMAX
−40°C ≤ TA ≤ 85°C
−40°C to +150°C
150°C
Supply Voltage
±2.25V to ±22V
Electrical Characteristics The following specifications apply for VS = ±22V, fIN = 1kHz, RL = 1kΩ, unless
otherwise specified. Typicals and limits apply for TA = 25°C.
LME49610
Units
(Limits)
Symbol
Parameter
Conditions
Typical
Limit
(Note 6)
(Note 7)
IOUT = 0
IQ
Total Quiescent Current
BW pin: No connect
BW pin: Connected to VEE pin
13
19
15
23
mA (max)
mA (max)
AV = 1, VOUT = 3VRMS
,
RL = 32Ω, BW = 80kHz,
closed loop see Figure 2.
f = 1kHz
Total Harmonic Distortion + Noise
(Note 8)
THD+N
SR
0.000035
0.0005
%
%
f = 20kHz
30 ≤ BW ≤ 180MHz
VOUT = 20VP-P, RL = 100Ω
Slew Rate
Bandwidth
2000
V/μs
AV = –3dB
BW pin: No Connect
RL = 100Ω
RL = 1kΩ
110
120
MHz
MHz
BW
BW pin: Connected to VEE pin
RL = 100Ω
RL = 1kΩ
180
200
MHz
MHz
f = 10kHz
BW pin: No Connect
3.0
2.7
8.5
6.5
nV/√Hz (max)
nV/√Hz (max)
Voltage Noise Density
Settling Time
f = 10kHz
BW pin: Connected to VEE pin
ΔV = 10V, RL = 100Ω
1% Accuracy
ts
BW pin: No connect
BW pin: Connected to VEE pin
200
60
ns
ns
VOUT = ±10V
RL = 67Ω
RL = 100Ω
RL = 1kΩ
0.93
0.95
0.99
0.90
0.92
0.98
V/V (min)
V/V (min)
V/V (min)
AV
Voltage Gain
3
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LME49610
Units
(Limits)
Symbol
Parameter
Conditions
Typical
Limit
(Note 6)
(Note 7)
Positive
IOUT = 10mA
VCC –1.2
VCC –1.5
VCC –1.7
VCC –1.4
VCC –1.8
VCC –2.1
V (min)
V (min)
V (min)
IOUT = 100mA
IOUT = 150mA
VOUT
Voltage Output
Negative
IOUT = –10mA
IOUT = –100mA
IOUT = –150mA
VEE +1.2
VEE +1.6
VEE +2.2
VEE +1.4
VEE +1.9
VEE +2.5
V (min)
V (min)
V (min)
IOUT
Output Current
±250
mA
BW pin: No Connect
BW pin: Connected to VEE pin
±750
±750
mA
mA (max)
IOUT-SC
Short Circuit Output Current
±785
VIN = 0V
IB
μA (max)
μA (max)
Input Bias Current
Input Impedance
BW pin: No Connect
BW pin: Connected to VEE pin
±1.0
±3.0
±2.5
±5.0
RL = 100Ω
BW pin: No Connect
BW pin: Connected to VEE pin
ZIN
MΩ
MΩ
7.5
5.5
VOS
Offset Voltage
±17
±60
mV (max)
VOS/°C
Offset Voltage vs Temperature
±100
40°C ≤ TA ≤ +125°C
μV/°C
Power Supply Voltage Operating
Range
±2.25
±22
V
V
V SUPPLY
Note 1: “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. The Recommended Operating Conditions indicate conditions at which the device is functional and the
device should not be operated beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified
Note 2: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified
or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed.
Note 3: 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 number given in Absolute Maximum Ratings, whichever is lower. For the LME49610, typical
application shown in Figure 2 with |VEE| = VCC = 15V, RL = 32Ω, the total power dissipation is 1.9W. θJA = 20°C/W for the TO-263 package mounted to 16in2
(103.2 cm2) 1oz. copper surface heat sink area.
Note 4: Human body model, applicable std. JESD22-A114C.
Note 5: Machine model, applicable std. JESD22-A115-A.
Note 6: 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 guaranteed.
Note 7: Datasheet min/max specification limits are guaranteed by test or statistical analysis.
Note 8: This is the distortion of the LME49610 operating in a closed loop configuration with an LME49710. When operating in an operational amplifier's feedback
loop, the amplifier's open loop gain dominates, linearizing the system and determining the overall system distortion.
Note 9: The TS5B package is a non-isolated package. The package’s metal back and any heat sink to which it is mounted are connected to the same potential
as the –VEE pin.
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Typical Performance Characteristics
Gain vs Frequency vs Quiescent Current
VS = ±22V
Phase vs Frequency vs Quiescent Current
VS = ±22V
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30042571
Gain vs Frequency vs Power Supply Voltage
Phase vs Frequency vs Supply Voltage
Wide BW Mode (BW pin = VEE
)
Wide BW Mode (BW pin = VEE)
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30042573
Gain vs Frequency vs Power Supply Voltage
Low IQ Mode (BW pin = Float)
Phase vs Frequency vs Power Supply Voltage
Low IQ Mode (BW pin = Float)
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30042575
5
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Gain vs Frequency vs RLOAD
Wide BW Mode (BW pin = VEE), VS = ±22V
Phase vs Frequency vs RLOAD
Wide BW Mode (BW pin = VEE), VS = ±22V
30042576
30042577
Gain vs Frequency vs RLOAD
Low IQ Mode (BW pin = Float), VS = ±22V
Phase vs Frequency vs RLOAD
Low IQ Mode (BW pin = Float), VS = ±22V
30042578
30042579
Gain vs Frequency vs Quiescent Current
VS = ±15V
Phase vs Frequency vs Quiescent Current
VS = ±15V
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30042594
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Gain vs Frequency vs RLOAD
Wide BW Mode (BW pin = VEE), VS = ±15V
Phase vs Frequency vs RLOAD
Wide BW Mode (BW pin = VEE), VS = ±15V
300425a2
30042591
Gain vs Frequency vs RLOAD
Low IQ Mode (BW pin = Float), VS = ±15V
Phase vs Frequency vs RLOAD
Low IQ Mode (BW pin = Float), VS = ±15V
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30042590
+PSRR vs Frequency
+PSRR vs Frequency
VS = ±15V and ±22V, Low IQ Mode
(BW pin = Float)
VS = +15V and ±22V, Wide BW Mode
(BW pin = VEE
)
30042595
30042597
7
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−PSRR vs Frequency
−PSRR vs Frequency
VS = ±15V and ±22V, Low IQ Mode
(BW pin = Float)
VS = ±15V and ±22V, Wide BW Mode
(BW pin = VEE
)
30042596
30042598
Quiescent Current vs Bandwidth Control Resistance
VS = ±15V (Bottom) & VS = ±22V (Top)
THD+N vs Output Voltage
VS = ±15V, RL = 32Ω, f = 1kHz
300425a6
30042585
Wide BW Noise Curve
Low IQ Noise Curve
(BW pin = Float)
(BW pin = VEE
)
30042586
30042587
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Typical Application Diagram
30042540
FIGURE 2. High Performance, High Fidelity LME49610 Audio Buffer Application
9
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The audio input signal is applied to the input jack (HP31 or
J1/J2) and dc-coupled to the volume control, VR1. The output
signal from VR1’s wiper is applied to the non-inverting input
of U2-A, an LME49720 High Performance, High Fidelity audio
operational amplifier. U2-A’s signal gain is set by resistors R2
and R4. To allow for a DC-coupled signal path and to ensure
minimal output DC voltage regardless of the closed-loop gain,
the other half of the U2 is configured as a DC servo. By con-
stantly monitoring U2-A’s output, the servo creates a voltage
that compensates for any DC voltage that may be present at
the output. A correction voltage is generated and applied to
the feedback node at U2-A, pin 2. The servo ensures that the
gain at DC is unity. Based on the values shown in Figure 3,
the RC combination formed by R11 and C7 sets the servo’s
high-pass cutoff at 0.16Hz. This is over two decades below
20Hz, minimizing both amplitude and phase perturbations in
the audio frequency band’s lowest frequencies.
Application Information
HIGH PERFORMANCE, HIGH FIDELITY HEADPHONE
AMPLIFIER
The LME49610 is the ideal solution for high output, high per-
formance high fidelity headphone amplifiers. When placed in
the feedback loop of the LME49710, LME49720 or
LME49740 High Performance, High Fidelity audio operational
amplifier, the LME49610 is able to drive 32Ω headphones to
a dissipation of greater than 500mW at 0.00003% THD+N
while operating on ±15V power supply voltages. The circuit
schematic for a typical headphone amplifier is shown in Fig-
ure 3.
Operation
The following describes the circuit operation for the head-
phone amplifier’s Left Channel. The Right Channel operates
identically.
30042558
FIGURE 3. LME49610 delivers high output current for this high performance headphone amplifier
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10
AUDIO BUFFERS
nected close to the LME49610’s power supply pins. Capacitor
values as low as 0.01μF to 0.1μF will ensure stable operation
in lightly loaded applications, but high output current and fast
output slewing can demand large current transients from the
power supplies. Place a recommended parallel combination
of a solid tantalum capacitor in the 5μF to 10μF range and a
ceramic 0.1μF capacitor as close as possible to the device
supply pins.
Audio buffers or unity-gain followers, have large current gain
and a voltage gain of one. Audio buffers serve many applica-
tions that require high input impedance, low output
impedance and high output current. They also offer constant
gain over a very wide bandwidth.
Buffers serve several useful functions, either in stand-alone
applications or in tandem with operational amplifiers. In stand-
alone applications, their high input impedance and low output
impedance isolates a high impedance source from a low
impedance load.
SUPPLY BYPASSING
The LME49610 will place great demands on the power supply
voltage source when operating in applications that require
fast slewing and driving heavy loads. These conditions can
create high amplitude transient currents. A power supply’s
limited bandwidth can reduce the supply’s ability to supply the
needed current demands during these high slew rate condi-
tions. This inability to supply the current demand is further
exacerbated by PCB trace or interconnecting wire induc-
tance. The transient current flowing through the inductance
can produce voltage transients.
For example, the LME49610’s output voltage can slew at a
typical 2000V/μs. When driving a 100Ω load, the di/dt current
demand is 20 A/μs. This current flowing through an induc-
tance of 50nH (approximately 1.5” of 22 gage wire) will pro-
duce a 1V transient. In these and similar situations, place the
parallel combination of a solid 5μF to 10μF tantalum capacitor
and a ceramic 0.1μF capacitor as close as possible to the
device supply pins.
30042560
FIGURE 5. Buffer Connections
OUTPUT CURRENT
The LME49610 can continuously source or sink 250mA. In-
ternal circuitry limits the short circuit output current to approx-
imately ±450mA. For many applications that fully utilize the
LME49610’s current source and sink capabilities, thermal dis-
sipation may be the factor that limits the continuous output
current.
Ceramic capacitor have very lower ESR (typically less than
10mΩ) and low ESL when compared to the same valued tan-
talum capacitor. The ceramic capacitors, therefore, have su-
perior AC performance for bypassing high frequency noise.
In less demanding applications that have lighter loads or low-
er slew rates, the supply bypassing is not as critical. Capacitor
values in the range of 0.01μF to 0.1μF are adequate.
The maximum output voltage swing magnitude varies with
junction temperature and output current. Using sufficient PCB
copper area as a heatsink when the metal tab of the
LME49610’s surface mount TO–263 package is soldered di-
rectly to the circuit board reduces thermal impedance. This in
turn reduces junction temperature. The PCB copper area
should be in the range of 2in2 to 6in2.
SIMPLIFIED LME49610 CIRCUIT DIAGRAM
The LME49610’s simplified circuit diagram is shown in Figure
4. The diagram shows the LME49610’s complementary emit-
ter follower design, bias circuit and bandwidth adjustment
node.
THERMAL PROTECTION
LME49610 power dissipated will cause the buffer’s junction
temperature to rise. A thermal protection circuit in the
LME49610 will disable the output when the junction temper-
ature exceeds 150°C. When the thermal protection is activat-
ed, the output stage is disabled, allowing the device to cool.
The output circuitry is enabled when the junction temperature
drops below 150°C.
The TO–263 package has excellent thermal characteristics.
To minimize thermal impedance, its exposed die attach pad-
dle should be soldered to a circuit board copper area for good
heat dissipation. Figure 6 shows typical thermal resistance
from junction to ambient as a function of the copper area. The
TO–263’s exposed die attach paddle is electrically connected
to the VEE power supply pin.
30042559
LOAD IMPEDANCE
FIGURE 4. Simplified Circuit Diagram
The LME49610 is stable under any capacitive load when driv-
en by a source that has an impedance of 50Ω or less. When
driving capacitive loads, any overshoot that is present on the
output signal can be reduced by shunting the load capaci-
tance with a resistor.
Figure 5 shows the LME49610 connected as an open-loop
buffer. The source impedance and optional input resistor,
RS, can alter the frequency response. As previously stated,
the power supplies should be bypassed with capacitors con-
11
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OVERVOLTAGE PROTECTION
A ground plane type circuit board layout is best for very high
frequency performance results. Bypass the power supply pins
(VCC and VEE) with 0.1μF ceramic chip capacitors in parallel
with solid tantalum 10μF capacitors placed as close as pos-
sible to the respective pins.
If the input-to-output differential voltage exceeds the
LME49610’s Absolute Maximum Rating of 3V, the internal
diode clamps shown in Figure 1 conduct, diverting current
around the compound emitter followers of Q1/Q5 (D1 – D7 for
positive input), or around Q2/Q6 (D8 – D14 for negative in-
puts). Without this clamp, the input transistors Q1/Q2 and Q5/
Q6 will zener and damage the buffer.
Source resistance can affect high-frequency peaking and
step response overshoot and ringing. Depending on the sig-
nal source, source impedance and layout, best nominal re-
sponse may require an additional resistance of 25Ω to
200Ω in series with the input. Response with some loads (es-
pecially capacitive) can be improved with an output series
resistor in the range of 10Ω to 150Ω.
To ensure that the current flow through the diodes is held to
a save level, the internal 200Ω resistor in series with the input
limits the current through these clamps. If the additional cur-
rent that flows during this situation can damage the source
that drives the LME49610’s input, add an external resistor in
series with the input see Figure 5.
THERMAL MANAGEMENT
Heat Sinking
BANDWITH CONTROL PIN
For some applications, the LME49610 may require a heat
sink. The use of a heat sink is dependent on the maximum
LME49610 power dissipation and a given application’s max-
imum ambient temperature. In the TO–263 package, heat
sinking the LME49610 is easily accomplished by soldering
the package’s tab to a copper plane on the PCB. (Note: The
tab on the LME49610’s TO–263 package is electrically con-
nected to VEE.)
The LME49610’s –3dB bandwidth is approximately 110MHz
in the low quiescent-current mode (13mA typical). Select this
mode by leaving the BW pin unconnected.
Connect the BW pin to the VEE pin to extend the LME49610’s
bandwidth to a nominal value of 180MHz. In this mode, the
quiescent current increases to approximately 19mA. Band-
widths between these two limits are easily selected by con-
necting a series resistor between the BW pin and VEE
.
Through the mechanisms of convection, heat conducts from
the LME49610 in all directions. A large percentage moves to
the surrounding air, some is absorbed by the circuit board
material and some is absorbed by the copper traces connect-
ed to the package’s pins. From the PCB material and the
copper, it then moves to the air. Natural convection depends
on the amount of surface area that contacts the air.
Regardless of the connection to the LME49610’s BW pin, the
rated output current and slew rate remain constant. With the
power supply voltage held constant, the wide-bandwidth
mode’s increased quiescent current causes a corresponding
increase in quiescent power dissipation. For all values of the
BW pin voltage, the quiescent power dissipation is equal to
the total supply voltage times the quiescent current (IQ
(VCC + |VEE |)).
*
If a heat conductive copper plane has perfect thermal con-
duction (heat spreading) through the plane’s total area, the
temperature rise is inversely proportional to the total exposed
area. PCB copper planes are, in that sense, an aid to con-
vection. These planes, however, are not thick enough to
ensure perfect heat conduction. Therefore, eventually a point
of diminishing returns is reached where increasing copper
area offers no additional heat conduction to the surrounding
air. This is apparent in Figure 6. 2 oz copper boards will have
decrease thermal resistance providing a better heat sink com-
pared to 1oz. copper. Beyond 1oz or 2oz copper plane areas,
external heatsinks are required. Ultimately, the 1oz copper
BOOSTING OP AMP OUTPUT CURRENT
When placed in the feedback loop, the LME49610 will in-
crease an operational amplifier’s output current. The opera-
tional amplifier’s open loop gain will correct any LME49610
errors while operating inside the feedback loop.
To ensure that the operational amplifier and buffer system are
closed loop stable, the phase shift must be low. For a system
gain of one, the LME49610 must contribute less than 20° at
the operational amplifier’s unity-gain frequency. Various op-
erating conditions may change or increase the total system
phase shift. These phase shift changes may affect the oper-
ational amplifier's stability.
Unity gain stability is preserved when the LME49610 is placed
in the feedback loop of most general-purpose or precision op
amps. When the LME46900 is driving high value capacitive
loads, the BW pin should be connected to the VEE pin for wide
bandwidth and stable operation. The wide bandwidth mode is
also suggested for high speed or fast-settling operational am-
plifiers. This preserves their stability and the ability to faithfully
amplify high frequency, fast-changing signals. Stability is en-
sured when pulsed signals exhibit no oscillations and ringing
is minimized while driving the intended load and operating in
the worst-case conditions that perturb the LME49610’s phase
response.
HIGH FREQUENCY APPLICATIONS
The LME49610’s wide bandwidth and very high slew rate
make it ideal for a variety of high-frequency open-loop appli-
cations such as an ADC input driver, 75Ω stepped volume
attenuator driver, and other low impedance loads. Circuit
board layout and bypassing techniques affect high frequency,
fast signal dynamic performance when the LME49610 oper-
ates open-loop.
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12
area attains a nominal value of 20°C/W junction to ambient
TA(MAX) = the maximum ambient temperature in the
thermal resistance (θJA) under zero air flow.
LME49610’s environment
PD(MAX) = the maximum recommended power dissipation
Note: The allowable thermal resistance is determined by the
maximum allowable temperature increase:
TRISE = TJ(MAX) - TA(MAX)
Thus, if ambient temperature extremes force TRISE to exceed
the design maximum, the part must be de-rated by either de-
creasing PD to a safe level, reducing θJA further, or, if avail-
able, using a larger copper area.
Procedure
1. First determine the maximum power dissipated by the
LME49610, PD(MAX). For the simple case of the buffer driving
a resistive load, and assuming equal supplies, PD(MAX) is giv-
en by:
2
PDMAX(AC) = (IS x VS) + (VS)2 / (2π RL) (Watts)
(2)
(3)
30042562
PDMAX(DC) = (IS x VS) + (VS)2 / RL (Watts)
FIGURE 6. Thermal Resistance (typ) for 5 lead TO-263
Package Mounted on 1oz. copper
where:
A copper plane may be placed directly beneath the tab. Ad-
ditionally, a matching plane can be placed on the opposite
side. If a plane is placed on the side opposite of the
LME49610, connect it to the plane to which the buffer’s metal
tab is soldered with a matrix of thermal vias per JEDEC Stan-
dard JESD51-5.
VS = |VEE| + VCC (V)
IS = quiescent supply current (A)
Equation (2) is for sinusoidal output voltages and (3) is for DC
output voltages
2. Determine the maximum allowable die temperature rise,
Determining Copper Area
Find the required copper heat sink area using the following
guidelines:
TRISE(MAX) = TJ(MAX) - TA(MAX) °C
(4)
1. Determine the maximum power dissipation of the
LME49610, PD.
3. Using the calculated value of TRISE(MAX) and PD(MAX), find
the required value of junction to ambient thermal resistance
combining equation 1 and equation 4 to derive equation 5:
2. Specify a maximum operating ambient temperature, TA
Note that the die temperature, TJ, will be higher than
(MAX).
TA by an amount that is dependent on the thermal resistance
from junction to ambient, θJA. Therefore, TA must be specified
such that TJ does not exceed the absolute maximum die tem-
perature of 150°C.
θ
JA = TRISE(MAX) / PD(MAX) (°C/W)
(5)
4. Finally, choose the minimum value of copper area from
Figure 6 based on the value for θJA
3. Specify a maximum allowable junction temperature, TJ
(MAX), This is the LME49610’s die temperature when the buffer
is drawing maximum current (quiescent and load). It is pru-
dent to design for a maximum continuous junction tempera-
ture of 100°C to 130°C. Ensure, however, that the junction
temperature never exceeds the 150°C absolute maximum
rating for the part.
.
Example
Assume the following conditions: VS = |VEE| + VCC = 30V,
RL = 32Ω, IS = 15mA, sinusoidal output voltage, TJ(MAX) = 125°
C, TA(MAX) = 85°C.
4. Calculate the value of junction to ambient thermal resis-
tance, θJA
.
Applying Equation (2):
5. θJA as a function of copper area in square inches is shown
in Figure 6. Choose a copper area that will guarantee the
specified TJ(MAX) for the calculated θJA. The maximum value
of junction to ambient thermal resistance, θJA, is defined as:
2
PDMAX = (IS x VS) + (VS)2 / 2π RL
= (15mA)(30V) + 900V2 / 632Ω
= 1.87W
θ
JA = (TJ(MAX) - TA(MAX) ) / PD(MAX) (°C/W)
(1)
Applying Equation (4):
where:
TJ(MAX) = the maximum recommended junction temperature
TRISE(MAX) = 125°C – 85°C
= 40°C
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SLEW RATE
Applying Equation (5):
A buffer’s voltage slew rate is its output signal’s rate of change
with respect to an input signal’s step changes. For resistive
loads, slew rate is limited by internal circuit capacitance and
operating current (in general, the higher the operating current
for a given internal capacitance, the higher the slew rate).
θ
JA = 40°C/1.87W
= 21.4°C/W
However, when driving capacitive loads, the slew rate may be
limited by the available peak output current according to the
following expression.
Examining the Copper Area vs. θJA plot (see Figure 6) indi-
cates that a thermal resistance of 21.4°C/W is possible with
a 8–10in2 plane of one layer of 1oz copper. Other solutions
include using two layers of 1oz copper or the use of 2oz cop-
per. Higher dissipation may require forced air flow. As a safety
margin, an extra 15% heat sinking capability is recommend-
ed.
dv/dt = IPK / CL
(6)
Output voltages with high slew rates will require large output
load currents. For example if the part is required to slew at
1000V/μs with a load capacitance of 1nF, the current de-
manded from the LME49610 is 1A. Therefore, fast slew rate
is incompatible with a capacitive load of this value. Also, if
CL is in parallel with the load, the peak current available to the
load decreases as CL increases.
When amplifying AC signals, wave shapes and the nature of
the load (reactive, non-reactive) also influence dissipation.
Peak dissipation can be several times the average with reac-
tive loads. It is particularly important to determine dissipation
when driving large load capacitance.
The LME49610’s dissipation in DC circuit applications is eas-
ily computed using Equation (3). After the value of dissipation
is determined, the heat sink copper area calculation is the
same as for AC signals.
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14
300425a7
FIGURE 7. High Speed Positive and Negative Regulator
15
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Revision History
Rev
1.0
Date
Description
04/09/08
10/28/09
Initial WEB released.
Typical and Limit changes on the Short Circuit Output current.
1.01
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16
Physical Dimensions inches (millimeters) unless otherwise noted
Order Number LME49610TS
See NS Package TS5B
17
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Notes
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