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| 型号： | A8514KLPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 27/42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
Step 4a Determining the duty cycle, calculated as follows:
Step 4d Double-check to make sure the ? current ripple is less
D (max) = 1 –
V IN (min)
V OUT(OVP) + V d
(12)
than I IN (min):
I IN (min) > 1 / 2 Δ I L
0.67 A > 0.19 A
(18)
= 1 –
10 (V)
35.36 (V) + 0.4 (V)
= 72.04%
A good inductor value to use would be 10 μ H.
Step 4e This step is used to verify that there is sufficient slope
3.6 f SW
Step 4b Determining the maximum and minimum input current
to the system. The minimum input current will dictate the induc-
tor value. The maximum current rating will dictate the current
rating of the inductor. First, the maximum input current, given:
compensation for the inductor chosen. The slope compensation
value is determined by the following formula:
Slope Compensation = = 3.6 A / μ s (19)
2 10 6
I OUT = # CHANNELS
I LED
(13)
Next insert the inductor value used in the design:
V IN (min)
then:
I IN (max) =
= 4 0.060 (A) = 0.240 A
V OUT(OVP) I OUT
(14)
Δ I Lused =
=
V IN (min) D (max)
L used f SW
10 (V) 0.72
10 ( μ H) 2.0 (MHz)
= 0.36 A
(20)
=
35.36 (V) 240 (mA)
10 (V) 0.90
= 0.94 A
Calculate the minimum required slope:
(1 – D (max))
where η is efficiency.
Next, calculate minimum input current, as follows:
Required Slope (min) =
Δ I Lused 1 10 – 6
1
f SW
(21)
I IN (min) =
V OUT(OVP)
V IN (max)
I OUT
(15)
=
0.36 (A)
1
2.0 (MHz)
1 10 – 6
(1 – 0.72)
= 2.57 A/ μ s
=
35.36 (V) 240 (mA)
14 (V) 0.90
= 0.67 A
If the minimum required slope is greater than the calculated slope
compensation, the inductor value must be increased.
A good approximation of efficiency, η , can be taken from the
efficiency curves located in the datasheet. A value of 90% is a
good starting approximation.
Step 4c Determining the inductor value. To ensure that the
inductor operates in continuous conduction mode, the value of
the inductor must be set such that the ? inductor ripple current is
Note: The slope compensation value is in A/ μ s, and 1 × 10 –6 is a
constant multiplier.
Step 4f Determining the inductor current rating. The inductor
current rating must be greater than the I IN (max) value plus the
ripple current Δ I L , calculated as follows:
not greater than the average minimum input current. A first past
assumes I ripple to be 40% of the maximum inductor current:
L (min) = I IN (max) + 1 / 2 Δ I Lused
= 0.94 (A) + 0.36 (A) / 2 = 1.12 A
(22)
then:
Δ I L = I IN (max) × I ripple
= 0.94 × 0.40 = 0.376 A
(16)
Step 5 Determining the resistor value for a particular switching
frequency. Use the R FSET values shown in figure 7. For example,
a 10 k Ω resistor will result in a 2 MHz switching frequency.
V IN (min)
L =
=
Δ I L f SW
D (max)
10 (V)
0.376 (A) 2 (MHz)
0.72 = 9.57 μ H
(17)
Step 6 Choosing the proper switching diode. The switching diode
must be chosen for three characteristics when it is used in LED
lighting circuitry. The most obvious two are: current rating of the
diode and reverse voltage rating.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
27
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