LM48555
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LM48555 Boomer® Audio Power Amplifier Series Ceramic Speaker Driver
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FEATURES
DESCRIPTION
•
•
•
•
•
The LM48555 is an audio power amplifier designed to
drive ceramic speakers in applications such as cell
phones, smart phones, PDAs and other portable
devices. The LM48555 produces 15.7VP-P with less
than 1% THD+N while operating from a 3.2V power
supply. The LM48555 features a low power shutdown
mode, and differential inputs for improved noise
rejection.
1
2
Fully Differential Amplifier
Externally Configurable Gain
Soft Start Function
Low Power Shutdown Mode
Under Voltage Lockout
APPLICATIONS
•
•
•
Mobile Phones
PDA's
Digital Cameras
KEY SPECIFICATIONS
•
•
•
IDDQ (Boost Converter + Amplifier) at VDD =
5V: 7.5mA (typ)
Output Voltage Swing VDD = 3.2V, THD ≤ 1%:
15.7VP-P (typ)
Power Supply Rejection Ratio f = 217Hz 80dB
(typ)
The LM48555 includes advanced click and pop
suppression that eliminates audible turn-on and turnoff transients. Additionally, the integrated boost
regulator features a soft start function that minimizes
transient current during power-up
Boomer audio power amplifiers were designed
specifically to provide high quality output power with a
minimal number of external components. The
LM48555 does not require bootstrap capacitors, or
snubber circuits.
The LM48555 is unity-gain stable and uses external
gain-setting resistors.
1
2
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.
All 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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LM48555
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Typical Application
VDD
L1
10 PH
D1
CS
4.7 PF
CO
10 PF
D3
C1
VDD
Bootstrap
D2
SW
VREF
PWM
D1
GND (SW)
LM48555
Shutdown
Control
C2
SD
C3
Soft Start
B1
IN+
CSS
0.1 PF
CIN+ RIN+
0.47 PF 20 k:
BIAS,
SHUTDOWN,
AND
PROTECTION
CIRCUITRY
VAMP
A2
OUT-
A1
RO
20:
CL
1 PF
B3
CIN- RIN0.47 PF 20 k:
OUT+
IN-
A3
GND
B2
RF+
200 k:
Ceramic
Speaker
Load
CF+
* 82 pF
RF200 k:
CF* 82
pF
* CF+ and CF- are optional. Refer to “SELECTING INPUT AND FEEDBACK CAPACITORS AND RESISTOR FOR
AUDIO AMPLIFIER” section.
Figure 1. Typical Audio Amplifier Application Circuit
2
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Connection Diagram
1
2
3
A
OUT-
VAMP
OUT+
B
IN+
GND
IN-
C
Bootstrap
SD
Soft Start
D
GND (SW)
SW
VDD
Figure 2. Top View
LM48555TL Bumps Down View
Package Number YZR0012Z1A
Figure 3. YZR0012 Package View (Bumps Up)
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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Absolute Maximum Ratings (1) (2) (3)
Supply Voltage (VDD)
9.5V
Storage Temperature
−65°C to +150°C
−0.3V to VDD + 0.3V
Input Voltage
Power Dissipation (4)
Internally limited
(5)
2000V
ESD Susceptibility
ESD Susceptibility (6)
200V
Junction Temperature
150°C
θJA (7)
Thermal Resistance
(1)
(2)
(3)
(4)
(5)
(6)
(7)
114°C/W
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 ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
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.
The value for θJA is measured with the LM48555 mounted on a 3” x 1.5” (76.2mm x 3.81mm) four layer board. The copper thickness for
all four layers is 0.5oz (roughly 0.18mm).
Operating Ratings
TMIN ≤ TA ≤ TMAX (1)
Temperature Range
−40°C ≤ TA ≤ +85°C
2.7V ≤ VDD ≤ 6.5V
Supply Voltage (VDD)
(1)
The value for θJA is measured with the LM48555 mounted on a 3” x 1.5” (76.2mm x 3.81mm) four layer board. The copper thickness for
all four layers is 0.5oz (roughly 0.18mm).
Electrical Characteristics (1) (2)
The following specifications apply for VDD = 3.2V and the conditions shown in “Typical Audio Amplifier Application Circuit”
(see Figure 1), unless otherwise specified. Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LM48555
Typical (3)
Limit (4)
(5)
Units
(Limits)
VIN = 0V, No Load
Quiescent Power Supply Current
in Boosted Ringer Mode
IDD
VDD = 5.0V
7.5
mA
VDD = 3.6V
10
VDD = 3.2V
12
15
mA (max)
SD = GND (6)
0.1
1
µA (max)
mA
ISD
Shutdown Current
VLH
Logic High Threshold Voltage
1.2
V (min)
VLL
Logic Low Threshold Voltage
0.4
V (max)
RPULLDOWN
Pulldown Resistor on SD pin
53
kΩ (min)
TWU
Wake-up Time
CSS = 0.1μF
Boost Converter Output Voltage
Voltage on
VAMP Pin
8.5
7.5
V (max)
V (min)
VAMP
(1)
(2)
(3)
(4)
(5)
(6)
4
80
100
8
ms
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 ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
Typicals are measured at 25°C and represent the parametric norm.
Limits are specified to AOQL (Average Outgoing Quality Level).
Datasheet min/max specification limits are specified by design, test, or statistical analysis.
Shutdown current is measured in a normal room environment. The SD pin should be driven as close as possible to GND for minimum
shutdown current.
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Electrical Characteristics(1)(2) (continued)
The following specifications apply for VDD = 3.2V and the conditions shown in “Typical Audio Amplifier Application Circuit”
(see Figure 1), unless otherwise specified. Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LM48555
Typical (3)
Limit (4)
(5)
Units
(Limits)
VOUT
Output Voltage Swing
THD = 1% (max); f = 1kHz
15.7
15
VP-P (min)
THD+N
Total Harmonic Distortion + Noise
VOUT = 14VP-P, f = 1kHz
0.05
0.5
% (max)
εOS
Output Noise
A-Weighted Filter, VIN = 0V
70
PSRR
Power Supply Rejection Ratio
VRIPPLE = 200mVp-p, f = 217Hz,
AV = 20dB
80
ISW
Switch Current Limit
VOS
Output Offset Voltage
CMRR
Common Mode Rejection Ratio
UVLO
Under-Voltage Lock Out
RDS(ON)
Switch ON resistance
0.3
µV
72
dB (min)
4.5
mV (max)
70
65
dB (min)
2.5
2.6
V (max)
2
0.5
Input referred
A
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Typical Performance Characteristics
THD+N vs Frequency
VO = 4.95VRMS, VDD = 3.2V,
ZL = 1μF + 20Ω
10
10
5
5
2
2
1
THD+N (%)
1
THD+N (%)
THD+N vs Frequency
VO = 4.95VRMS, VDD = 4.2V,
ZL = 1μF + 20Ω
0.5
0.2
0.1
0.5
0.2
0.1
0.05
0.05
0.02
0.02
0.01
100
1k
300
2k
4k
0.01
100
10k
FREQUENCY (Hz)
10
2k
1k
300
4k
10k
FREQUENCY (Hz)
Figure 4.
Figure 5.
THD+N vs Frequency
VO = 4.95VRMS, VDD = 5V,
ZL = 1μF + 20Ω
THD+N vs Output Voltage Swing
VDD = 3.2V, ZL = 1μF + 20Ω
10
5
2
f = 10 kHz
1
f = 1 kHz
THD+N (%)
1
THD+N (%)
0.5
0.2
0.1
0.05
0.1
0.01
0.02
0.01
100
f = 100 Hz
1k
300
2k
4k
10k
0.001
10m
FREQUENCY (Hz)
1
Figure 6.
Figure 7.
THD+N vs Output Voltage Swing
VDD = 4.2V, ZL = 1μF + 20Ω
THD+N vs Output Voltage Swing
VDD = 5V, ZL = 1μF + 20Ω
f = 10 kHz
f = 1 kHz
1
THD+N (%)
1
0.1
0.01
f = 10 kHz
f = 1 kHz
0.1
0.01
f = 100 Hz
0.001
10m
100m
f = 100 Hz
1
10
0.001
10m
OUTPUT VOLTAGE SWING (VRMS)
100m
1
10
OUTPUT VOLTAGE SWING (VRMS)
Figure 8.
6
10
10
10
THD+N (%)
100m
OUTPUT VOLTAGE SWING (VRMS)
Figure 9.
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Typical Performance Characteristics (continued)
CMRR vs Frequency
VDD = 4.2V, ZL = 1μF + 20Ω
VIN = 100mVP-P
0
0
-10
-10
-20
-20
-30
-30
-40
-40
CMRR (dB)
CMRR (dB)
CMRR vs Frequency
VDD = 3.2V, ZL = 1μF + 20Ω
VIN = 100mVP-P
-50
-60
-50
-60
-70
-70
-80
-80
-90
-90
-100
20
100
1k
5k
-100
20
20k
100
Figure 11.
CMRR vs Frequency
VDD = 5V, ZL = 1μF + 20Ω
VIN = 100mVP-P
PSRR vs Frequency
VDD = 3.2V, ZL = 1μF + 20Ω
VRIPPLE = 200mVP-P
0
0
-10
-10
-20
-20
-30
-30
-40
-50
-60
-40
-50
-60
-70
-70
-80
-80
-90
-90
-100
20
-100
20
100
1k
5k
20k
100
1k
5k
Figure 13.
PSRR vs Frequency
VDD = 4.2V, ZL = 1μF + 20Ω
VRIPPLE = 200mVP-P
PSRR vs Frequency
VDD = 5V, ZL = 1μF + 20Ω
VRIPPLE = 200mVP-P
0
-10
-20
-20
-30
-30
-40
-40
PSRR (dB)
0
-10
-50
-60
-50
-60
-70
-70
-80
-80
-90
-90
-100
20
-100
20
1k
20k
FREQUENCY (Hz)
Figure 12.
100
20k
FREQUENCY (Hz)
FREQUENCY (Hz)
PSRR (dB)
5k
Figure 10.
PSRR (dB)
CMRR (dB)
FREQUENCY (Hz)
1k
5k
20k
FREQUENCY (Hz)
100
1k
5k
20k
FREQUENCY (Hz)
Figure 14.
Figure 15.
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Typical Performance Characteristics (continued)
Inductor Current vs Output Voltage Swing
ZL = 1μF + 20Ω, f = 1kHz,
VDD = 3V, 4.2V, 5V
Supply Current vs Supply Voltage
16
120
SUPPLY CURRENT (mA)
INDUCTOR CURRENT (mA)
14
100
80
60
40
20
0
10
8
6
4
2
0
1
2
3
4
5
6
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE SWING (VRMS)
Figure 16.
8
12
Figure 17.
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APPLICATION INFORMATION
CHARACTERISTICS OF CERAMIC SPEAKERS
Because of their ultra-thin profile piezoelectric ceramic speakers are ideal for portable applications. Piezoelectric
materials have high dielectric constants and their component electrical property is like a capacitor. Therefore,
piezoelectric ceramic speakers essentially represent capacitive loads over frequency. Because these speakers
are capacitive rather than resistive, they require less current than traditional moving coil speakers. However,
ceramic speakers require high driving voltages (approximately 15VP-P). To achieve these high output voltages in
battery operated applications, the LM48555 integrates a boost converter with an audio amplifier. High quality
piezoelectric ceramic speakers are manufactured by TayioYuden (www.t-yuden.com). Tayio Yuden's MLS-A
Series Ceramic Speaker series is recommended.
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM48555 includes a fully differential audio amplifier that features differential input and output stages.
Internally this is accomplished by two circuits: a differential amplifier and a common mode feedback amplifier that
adjusts the output voltages so that the average value remains VDD/2. When setting the differential gain, the
amplifier can be considered to have "halves". Each half uses an input and feedback resistor (RIN_ and RF_) to
set its respective closed-loop gain (see Figure 1). With RIN+ = RIN- and RF+ = RF-, the gain is set at -RF/RIN
for each half. This results in a differential gain of
AVD = -RF/RIN
(1)
It is extremely important to match the input resistors, as well as the feedback resistors to each other for best
amplifier performance. A differential amplifier works in a manner where the difference between the two input
signals is amplified. In most applications, this would require input signals that are 180° out of phase with each
other. The LM48555 can be used, however, as a single-ended input amplifier while still retaining its fully
differential benefits. In fact, completely unrelated signals may be placed at the input pins. The LM48555 simply
amplifies the difference between them.
The LM48555 provides what is known as a "bridged mode" output (bridge-tied-load, BTL). This results in output
signals at OUT+ and OUT- that are 180° out of phase with respect to each other. Bridged mode operation is
different from the traditional single-ended amplifier configuration that connects the load between the amplifier
output and ground. A bridged amplifier design has advantages over the single-ended configuration: it provides
differential drive to the load, thus doubling maximum possible output swing for a specific supply voltage. Up to
four times the output power is possible compared with a single-ended amplifier under the same conditions.
A bridged configuration, such as the one used in the LM48555, also creates a second advantage over singleended amplifiers. Since the differential outputs, OUT+ and OUT-, are biased at half-supply, no net DC voltage
exists across the load. This assumes that the input resistor pair and the feedback resistor pair are properly
matched. BTL configuration eliminates the output coupling capacitor required in single supply, single-ended
amplifier configurations. If an output coupling capacitor is not used in a single-ended output configuration, the
half-supply bias across the load would result in both increased internal IC power dissipation as well as
permanent loudspeaker damage.
BOOST CONVERTER POWER DISSIPATION
At higher duty cycles, the increased ON-time of the switch FET means the maximum output current will be
determined by power dissipation within the LM48555 FET switch. The switch power dissipation from ON-time
conduction is calculated by Equation 2.
PD(SWITCH) = DC x (IINDUCTOR(AVE))2 x RDS(ON) (W)
where
•
DC is the duty cycle
(2)
There will be some switching losses in addition to the power loss calculated in Equation 2, so some derating
needs to be applied when calculating IC power dissipation. See “MAXIMUM TOTAL POWER DISSIPATION”
section.
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MAXIMUM AMPLIFIER POWER DISSIPATION
Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or
single-ended. A direct consequence of the increased power delivered to the load by a bridge amplifier is an
increase in internal power dissipation. Since the amplifier portion of the LM48555 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 3.
PDMAX(AMP) = (2VDD2) / (π2RO) (W)
(3)
MAXIMUM TOTAL POWER DISSIPATION
The total power dissipation for the LM48555 can be calculated by adding Equation 2 and Equation 3 together to
establish Equation 4:
PDMAX(TOTAL) = (2VDD2) / (π2EFF2RO) (W)
where
•
EFF = Efficiency of boost converter
(4)
The result from Equation 4 must not be greater than the power dissipation that results from Equation 5:
PDMAX = (TJMAX - TA) / θJA (W)
(5)
For the YZR0012Z1A, θJA = 114°C/W. TJMAX = 150°C for the LM48555. 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 decreased, the load impedance increased or TA reduced. 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.
STARTUP SEQUENCE
Correct startup sequencing is important for optimal device performance. Using the correct startup sequence will
improve click and pop performance as well as avoid transients that could reduce battery life. The device should
be in Shutdown mode when the supply voltage is applied. Once the supply voltage has been supplied the device
can be released from Shutdown mode.
SHUTDOWN FUNCTION
In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry to
provide a quick, smooth transition into shutdown. Another solution is to use a single-pole, single-throw switch
connected between VDD and Shutdown pins.
BOOTSTRAP PIN
The bootstrap pin provides a voltage supply for the internal switch driver. Connecting the bootstrap pin to VAMP
(See Figure 1) allows for a higher voltage to drive the gate of the switch thereby reducing the RDS(ON). This
configuration is necessary in applications with heavier loads. The bootstrap pin can be connected to VDD when
driving lighter loads to improve device performance (IDD, THD+N, Noise, etc.).
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
LM48555 are multi-layer ceramic capacitors. They have the lowest ESR (equivalent series resistance) and
highest resonance frequency, which makes them optimum for high frequency switching converters. When
selecting a ceramic capacitor, only X5R and X7R dielectric types should be used. Other types such as Z5U and
Y5F have such severe loss of capacitance due to effects of temperature variation and applied voltage, they may
provide as little as 20% of rated capacitance in many typical applications. Always consult capacitor
manufacturer’s data curves before selecting a capacitor. High-quality ceramic capacitors can be obtained from
Taiyo-Yuden and Murata.
10
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POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection. The capacitor location on both V1 and VDD pins should be as close to the device as possible.
SELECTING INPUT AND FEEDBACK CAPACITORS AND RESISTOR FOR AUDIO AMPLIFIER
Special care must be taken to match the values of the feedback resistors (RF+ and RF-) to each other as well as
matching the input resistors (RIN+ and RIN-) to each other (see Typical Application). Because of the balanced
nature of differential amplifiers, resistor matching differences can result in net DC currents across the load. This
DC current can increase power consumption, internal IC power dissipation, reduce PSRR, and possibly damage
the loudspeaker. To achieve best performance with minimum component count, it is highly recommended that
both the feedback and input resistors match to 1% tolerance or better.
The input coupling capacitors, CIN, forms a first order high pass filter which limits low frequency response. This
value should be chosen based on needed frequency response. High value input capacitors are both expensive
and space hungry in portable designs. A certain value capacitor is needed to couple in low frequencies without
severe attenuation. Ceramic speakers used in portable systems, whether internal or external, have little ability to
reproduce signals below 100Hz to 150Hz. Thus, using a high value input capacitor may not increase actual
system performance. In addition to system cost and size, click and pop performance is affected by the value of
the input coupling capacitor, CIN. A high value input coupling capacitor requires more charge to reach its
quiescent DC voltage (nominally 1/2 VDD). This charge comes from the output via the feedback and is apt to
create pops upon device enable. Thus, by minimizing the capacitor value based on desired low frequency
response, turn-on pops can be minimized.
The LM48555 is unity-gain stable which gives the designer maximum system flexibility. However, to drive
ceramic speakers, a typical application requires a closed-loop differential gain of 10V/V. In this case, feedback
capacitors (CF+, CF-) may be needed as shown in Figure 1 to bandwidth limit the amplifier. If the available input
signal is bandwith limited, then capacitors CF+ and CF- can be eliminated. These feedback capacitors create a
low pass filter that eliminates possible high frequency noise. Care should be taken when calculating the -3dB
frequency (from Equation 6) because an incorrect combination of RF and CF will cause rolloff before the desired
frequency.
f–3dB = 1 / 2πRF*CF
(6)
SELECTING OUTPUT CAPACITOR (CO) FOR BOOST CONVERTER
A single 4.7μF to 10μF ceramic capacitor will provide sufficient output capacitance for most applications. If larger
amounts of capacitance are desired for improved line support and transient response, tantalum capacitors can
be used. Aluminum electrolytics with ultra low ESR such as Sanyo Oscon can be used. Typical electrolytic
capacitors are not suitable for switching frequencies above 500 kHz because of significant ringing and
temperature rise due to self-heating from ripple current. An output capacitor with excessive ESR can also reduce
phase margin and cause instability. In general, if electrolytics are used, it is recommended that they be paralleled
with ceramic capacitors to reduce ringing, switching losses, and output voltage ripple.
SELECTING A POWER SUPPLY 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 4.7μF is recommended, but larger values can be used. Since this capacitor reduces
the amount of voltage ripple seen at the input pin, it also reduces the amount of EMI passed back along that line
to other circuitry.
SELECTING A SOFT-START CAPACITOR (CSS)
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 startup. Selecting a soft-start capacitor (CSS)
value presents a trade off between the wake-up time and the startup transient current. Using a larger capacitor
value will increase wake-up time and decrease startup 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 (CO). A 0.1uF soft-start capacitor is recommended for a typical application.
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SELECTING DIODES
The external diode used in Figure 1 should be a Schottky diode. A 20V diode such as the MBR0520 from
Fairchild Semiconductor or ON Semiconductor is recommended. The MBR05XX series of diodes are designed to
handle a maximum average current of 0.5A. For applications exceeding 0.5A average but less than 1A, a
Microsemi UPS5817 can be used.
OUTPUT VOLTAGE OF BOOST CONVERTER
The output voltage is set using two internal resistors. The output voltage of the boost converter is set to 8V (typ).
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 Equation 7:
Duty Cycle = (VAMP+VDIODE -VDD)/(VAMP+VDIODE-VSW)
(7)
This applies for continuous mode operation.
INDUCTANCE 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 x IP2
where
•
“lP” is the peak inductor current
(8)
The LM48555 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.
INDUCTOR SUPPLIERS
The recommended inductors for the LM48555 are the Taiyo-Yuden NR4012, NR3010, and CBC3225 series and
Murata's LQH3NPN series. 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 core (switching) losses, and
wire power losses must be considered when selecting the current rating.
CALCULATING OUTPUT CURRENT OF BOOST CONVERTER (IAMP)
The load current of the boost converter is related to the average inductor current by the relation:
IAMP = IINDUCTOR(AVE) x (1 - DC) (A)
where
•
"DC" is the duty cycle of the application
(9)
The switch current can be found by:
ISW = IINDUCTOR(AVE) + 1/2 (IRIPPLE) (A)
(10)
Inductor ripple current is dependent on inductance, duty cycle, supply voltage and frequency:
IRIPPLE = DC x (VDD-VSW) / (f x
where
•
f = switching frequency = 1MHzL) (A)
(11)
combining all terms, we can develop an expression which allows the maximum available load current to be
calculated:
12
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Copyright © 2007–2013, Texas Instruments Incorporated
Product Folder Links: LM48555
LM48555
www.ti.com
SNAS400B – MARCH 2007 – REVISED MAY 2013
IAMP(max) = (1–DC)x[ISW(max)–DC(V-VSW)]/2fL (A)
(12)
The equation shown to calculate maximum load current takes into account the losses in the inductor or turn-off
switching losses of the FET and diode.
DESIGN PARAMETERS VSW AND ISW
The value of the FET "ON" voltage (referred to as VSW in Equation 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.
EVALUATION BOARD AND PCB LAYOUT GUIDELINES
For information on the LM48555 demo board and PCB layout guidelines refer to Application Notes AN-1611
(Literature Number SNAA041).
Revision History
Rev
Date
Description
1.0
03/15/07
Initial Web Release.
1.01
07/27/12
Deleted the Murata references on Application Information.
B
05/02/2013
Changed layout of National Data Sheet to TI format.
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Copyright © 2007–2013, Texas Instruments Incorporated
Product Folder Links: LM48555
13
PACKAGE OPTION ADDENDUM
www.ti.com
29-Aug-2015
PACKAGING INFORMATION
Orderable Device
Status
(1)
LM48555TL/NOPB
ACTIVE
Package Type Package Pins Package
Drawing
Qty
DSBGA
YZR
12
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
TBD
Call TI
Call TI
Op Temp (°C)
Device Marking
(4/5)
-40 to 85
G
I4
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
29-Aug-2015
Addendum-Page 2
MECHANICAL DATA
YZR0012xxx
0.600±0.075
D
E
TLA12XXX (Rev C)
4215049/A
NOTES:
A. All linear dimensions are in millimeters. Dimensioning and tolerancing per ASME Y14.5M-1994.
B. This drawing is subject to change without notice.
www.ti.com
12/12
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