- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄358868 > LM4961 (National Semiconductor Corporation) Ceramic Speaker Driver PDF資料下載
參數(shù)資料
| 型號(hào)： | LM4961 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Ceramic Speaker Driver |
| 中文描述： | 陶瓷揚(yáng)聲器驅(qū)動(dòng)器 |
| 文件頁(yè)數(shù)： | 11/16頁(yè) |
| 文件大?。?/td> | 509K |
| 代理商： | LM4961 |
第1頁(yè)第2頁(yè)第3頁(yè)第4頁(yè)第5頁(yè)第6頁(yè)第7頁(yè)第8頁(yè)第9頁(yè)第10頁(yè)當(dāng)前第11頁(yè)第12頁(yè)第13頁(yè)第14頁(yè)第15頁(yè)第16頁(yè)
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 = V
OUT
+ V
DIODE
- V
IN
/
V
OUT
+ V
DIODE
- V
SW
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 “l(fā)p” 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:
V
IN
= 5V, V
OUT
= 12V, V
DIODE
= 0.5V, V
SW
= 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:
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 (I
AMP
)
As shown in Figure 2 which depicts inductor current, the load
current is related to the average inductor current by the
relation:
I
LOAD
= I
IND
(AVG) x (1 - DC)
(7)
Where "DC" is the duty cycle of the application. The switch
current can be found by:
I
SW
= I
IND
(AVG) + 1/2 (I
RIPPLE
)
(8)
Inductor ripple current is dependent on inductance, duty
cycle, input voltage and frequency:
I
RIPPLE
= DC x (V
IN
-V
SW
) / (f x L)
(9)
combining all terms, we can develop an expression which
allows the maximum available load current to be calculated:
I
LOAD
(max) = (1–DC)x(I
SW
(max)–DC(V
IN
-V
SW
))/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.
20094099
FIGURE 3. 10μH Inductor Current
5V - 12V Boost (LM4961X)
L
www.national.com
11
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM4961LQ | Ceramic Speaker Driver |
| LM4970 | Audio Synchronized Color LED Driver |
| LM4990ITL | 2 Watt Audio Power Amplifier with Selectable Shutdown Logic Level |
| LM4990ITLX | 2 Watt Audio Power Amplifier with Selectable Shutdown Logic Level |
| LM4990MM | 2 Watt Audio Power Amplifier with Selectable Shutdown Logic Level |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4961LQ | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4961LQ/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4961LQBD | 功能描述:音頻 IC 開發(fā)工具 LM4961LQ EVAL BOARD RoHS:否 制造商:Texas Instruments 產(chǎn)品:Evaluation Kits 類型:Audio Amplifiers 工具用于評(píng)估:TAS5614L 工作電源電壓:12 V to 38 V |
| LM4961LQBD/NOPB | 制造商:Texas Instruments 功能描述:Evaluation Kit For Ceramic Speaker Driver |
| LM4961LQX | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。