|
|
PDF LM4961 Data sheet ( Hoja de datos )
| Número de pieza | LM4961 | |
| Descripción | Ceramic Speaker Driver | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LM4961 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
|
No Preview Available !
October 2004
LM4961
Ceramic Speaker Driver
General Description
The LM4961 is an audio power amplifier primarily designed
for driving Ceramic Speaker for applications in Cell Phone
and PDAs. It integrates a boost converter, with variable
output voltage, with an audio power amplifier. It is capable of
driving 15Vp-p in BTL mode to 2uF+ 30 ohms load, continu-
ous average power, with less than 1% distortion (THD+N)
from a 3.2VDC power supply.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal number of
external components. The LM4961 does not require boot-
strap capacitors, or snubber circuits therefore it is ideally
suited for portable applications requiring high voltage output
to drive capacitive loads like Ceramic Speakers. The
LM4961 features a low-power consumption shutdown mode.
Additionally, the LM4961 features an internal thermal shut-
down protection mechanism.
The LM4961 contains advanced pop & click circuitry that
eliminates noises which would otherwise occur during
turn-on and turn-off transitions.
The LM4961 is unity-gain stable and can be configured by
external gain-setting resistors.
Key Specifications
n Quiescent Power Supply Current
n Voltage Swing in BTL at 1% THD
n Shutdown current
7mA (typ)
15Vp-p (typ)
0.1µA (typ)
Features
n Pop & click circuitry eliminates noise during turn-on and
turn-off transitions
n Low current shutdown mode
n Low quiescent current
n Mono 15Vp-p BTL output, RL = 2µF+30Ω, f = 1kHz
n Thermal shutdown protection
n Unity-gain stable
n External gain configuration capability
n Including Band exchange SW
n Including Leakage cut SW
Applications
n Cellphone
n PDA
Connection Diagram
LM4961LQ (5x5)
Top View
Order Number LM4XXX
See NS Package Number
20094084
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2004 National Semiconductor Corporation DS200940
www.national.com
1 page  
Typical Performance Characteristics
THD+N vs Frequency
VDD = 4.2V, VO = 14VP-P, RL = 2µF+30Ω
THD+N vs Frequency
VDD = 3.2V, VO = 14VP-P, RL = 2µF+30Ω
20094087
THD+N vs Output Voltage
VDD = 4.2V, RL = 2µF + 30Ω
200940C3
THD+N vs Output Voltage
VDD = 3.2V, RL = 2µF + 30Ω
200940C4
PSRR vs Frequency
VDD = 4.2V, RL = 8Ω, VRIPPLE = 200mVP-P
200940C5
PSRR vs Frequency
VDD = 3.2V, RL = 8Ω, VRIPPLE = 20mVP-P
20094089
5
20094090
www.national.com
5 Page 
Application Information (Continued)
DUTY CYCLE
The maximum duty cycle of the boost converter determines
the maximum boost ratio of output-to-input voltage that the
converter can attain in continuous mode of operation. The
duty cycle for a given boost application is defined as:
Duty Cycle = VOUT + VDIODE - VIN / VOUT + VDIODE - VSW
This applies for continuous mode operation.
INDUCTANCE VALUE
The first question we are usually asked is: “How small can I
make the inductor.” (because they are the largest sized
component and usually the most costly). The answer is not
simple and involves trade-offs in performance. Larger induc-
tors mean less inductor ripple current, which typically means
less output voltage ripple (for a given size of output capaci-
tor). Larger inductors also mean more load power can be
delivered because the energy stored during each switching
cycle is:
E = L/2 X (lp)2
Where “lp” is the peak inductor current. An important point to
observe is that the LM4961 will limit its switch current based
on peak current. This means that since lp(max) is fixed,
increasing L will increase the maximum amount of power
available to the load. Conversely, using too little inductance
may limit the amount of load current which can be drawn
from the output.
Best performance is usually obtained when the converter is
operated in “continuous” mode at the load current range of
interest, typically giving better load regulation and less out-
put ripple. Continuous operation is defined as not allowing
the inductor current to drop to zero during the cycle. It should
be noted that all boost converters shift over to discontinuous
operation as the output load is reduced far enough, but a
larger inductor stays “continuous” over a wider load current
range.
To better understand these trade-offs, a typical application
circuit (5V to 12V boost with a 10µH inductor) will be ana-
lyzed. We will assume:
VIN = 5V, VOUT = 12V, VDIODE = 0.5V, VSW = 0.5V
Since the frequency is 1.6MHz (nominal), the period is ap-
proximately 0.625µs. The duty cycle will be 62.5%, which
means the ON-time of the switch is 0.390µs. It should be
noted that when the switch is ON, the voltage across the
inductor is approximately 4.5V. Using the equation:
V = L (di/dt)
We can then calculate the di/dt rate of the inductor which is
found to be 0.45 A/µs during the ON-time. Using these facts,
we can then show what the inductor current will look like
during operation:
20094099
FIGURE 3. 10µH Inductor Current
5V - 12V Boost (LM4961X)
During the 0.390µs ON-time, the inductor current ramps up
0.176A and ramps down an equal amount during the OFF-
time. This is defined as the inductor “ripple current”. It can
also be seen that if the load current drops to about 33mA,
the inductor current will begin touching the zero axis which
means it will be in discontinuous mode. A similar analysis
can be performed on any boost converter, to make sure the
ripple current is reasonable and continuous operation will be
maintained at the typical load current values. Taiyo-Yudens
NR4012 inductor series is recommended.
MAXIMUM SWITCH CURRENT
The maximum FET switch current available before the cur-
rent limiter cuts in is dependent on duty cycle of the appli-
cation. This is illustrated in a graph in the typical perfor-
mance characterization section which shows typical values
of switch current as a function of effective (actual) duty cycle.
CALCULATING OUTPUT CURRENT OF BOOST
CONVERTER (IAMP)
As shown in Figure 2 which depicts inductor current, the load
current is related to the average inductor current by the
relation:
ILOAD = IIND(AVG) x (1 - DC)
(7)
Where "DC" is the duty cycle of the application. The switch
current can be found by:
ISW = IIND(AVG) + 1/2 (IRIPPLE)
(8)
Inductor ripple current is dependent on inductance, duty
cycle, input voltage and frequency:
IRIPPLE = DC x (VIN-VSW) / (f x L)
(9)
combining all terms, we can develop an expression which
allows the maximum available load current to be calculated:
ILOAD(max) = (1–DC)x(ISW(max)–DC(VIN-VSW))/2FL(10)
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.
11 www.national.com
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LM4961.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LM4960 | Piezoelectric Speaker Driver | National Semiconductor |
| LM4960 | LM4960 Piezoelectric Speaker Driver (Rev. C) |  Texas Instruments |
| LM4960SQ | Piezoelectric Speaker Driver | National Semiconductor |
| LM4961 | Ceramic Speaker Driver | National Semiconductor |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |