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参数资料
| 型号： | A8514KLPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 39/42页 |
| 文件大小： | 0K |
| 描述： | IC LED DVR WHT 4X80MA 16-ETSSOP |
| 标准包装： | 8,000 |
| 拓扑： | PWM，SEPIC，升压（升压） |
| 输出数： | 4 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 车载，背光 |
| 类型 - 次要： | 白色 LED |
| 频率： | 580kHz ~ 2MHz |
| 电源电压： | 5 V ~ 40 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-TSSOP（0.173"，4.40mm 宽）裸露焊盘 |
| 供应商设备封装： | 20-TSSOP-EP |
| 包装： | 带卷 (TR) |
| 工作温度： | -40°C ~ 125°C |
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A8514
Wide Input Voltage Range, High Efficiency
Fault Tolerant LED Driver
The error amplifier pole frequency is selected to compen-
sate for or cancel the power train ESR zero. This is the case if
the frequency of the ESR zero is small or below the switch-
ing frequency. Otherwise, it is selected to be at half switching
frequency. This pole frequency determines the end of mid-band
1c. To compensate for the difference from the error amplifier gain
at f ZEA and the actual mid-band gain, subtract an additional 3 dB:
–G P (f C ) –3 dB (A-29)
1d. Convert the calculated gain to a linear gain:
gain of the error amplifier transfer function, so it ensures that the
closed loop system cross-over frequency is below half switch-
ing frequency, which is important for stability issues. The pole
10
– G P (f C ) –3
20
(A-29)
f PEA =
frequency is defined by:
1
2 × × R Z ×
C Z × C P
C Z + C P
(A-27)
1e. Calculate R Z :
R Z =
10
g ×
– G P (f C ) –3
20
R S
R S +R D
(A-30)
Stabilizing the Closed Loop System
In this section, calculations are provided for selecting optimal
R Z , C Z , and C P . The closed loop system will be stable if the total
system transfer function rolls off while crossing over at a phase
margin of approximately 90° or –20 dB per decade. It is recom-
mended that the phase margin does not fall below 45°. For higher
2. Select a value for C Z .
2a. Calculate the frequency for the error-amplifier compensation
zero, f ZEA . This zero should cancel the dominant low frequency
pole of power train. Therefore, f ZEA should be close to f P . Usu-
ally it is selected to be 1 / 5 to 1 / 10 of f C :
stability, the cross over frequency should be much less than
the right half plane zero and smaller than half of the switching
frequency.
To achieve that, first fix the mid-band gain of the error amplifier
f ZEA = f C / 10
2b. Cz can be calculated by applying equation A-26:
C Z = 1 / (2 × π × R Z × f ZEA )
(A-31)
(A-32)
transfer function. Make it equal in value to the power train gain
at the cross over frequency, but negative so the total closed loop
gain will be 0 dB. Then position the compensation pole and zero.
Here are step-by-step procedures on how to calculate the com-
pensation network components:
1. Calculate R Z such that the negative mid-band gain of the error
amplifier will be equal to the power train gain at the required
system bandwidth or cross over frequency.
1a. Calculate the cross over frequency to be much less than
the RHP zero and lower than the half-switching frequency. A
20 to 30 kHz cross over frequency is appropriate for LED appli-
cations, calculated as follows:
3. Select a value for C P .
3a. Select a frequency for the error-amplifier compensation
pole, f PEA . This pole determines the error-amplifier end of the
mid-band region. It is selected to cancel the power train ESR
zero. However, if ceramic capacitors are used at the output, the
ESR zero will be at very high frequency. In this case, the f PEA is
selected to be at half of the switching frequency to ensure that
f C is at lower than half the switching frequency and as a result a
higher phase margin can be achieved. f PEA is given by:
f PEA = 0.5 × f SW (A-33)
3b. C P can be calculated by applying equation A-27:
f C = 0.015 × f SW (A-28)
1b. Calculate, or preferably measure, the power train gain at f C ,
which is G P (f C ), then multiply it by –1.
C P =
C Z
2 × × R Z × C Z × f PEA – 1
Allegro MicroSystems, LLC
115 Northeast Cutoff
(A-34)
A-4
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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