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| 型号： | A8514KLPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 28/42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 reverse voltage rating should be such that during operation
condition, the voltage rating of the device is larger than the maxi-
The rms current through the capacitor is given by:
? I Lused
I IN (max) × 12
mum output voltage. In this case it isV OUT(OVP) .
The peak current through the diode is calculated as:
I dp = I IN (max) + 1 / 2 Δ I Lused
(23)
I COUT rms = I OUT
D (max) +
1 – D (max)
(25)
0.72 +
= 0.94 (A) + 0.36 (A) / 2 = 1.12A
The third major component in deciding the switching diode is the
reverse current, I R , characteristic of the diode. This characteristic
is especially important when PWM dimming is implemented.
= 0.240 (A)
0.36 (A)
0.94 (A) × 12
1 – 0.72
= 0.39 A
During PWM off-time the boost converter is not switching. This
results in a slow bleeding off of the output voltage, due to leakage
currents. I R can be a large contributor, especially at high tempera-
tures. On the diode that was selected in this design, the current
varies between 1 and 100 μ A.
Step 7 Choosing the output capacitors. The output capacitors
must be chosen such that they can provide filtering for both the
boost converter and for the PWM dimming function. The biggest
factors that contribute to the size of the output capacitor are:
PWM dimming frequency and PWM duty cycle. Another major
contributor is leakage current, I LK . This current is the combina-
tion of the OVP leakage current as well as the reverse current of
The output capacitor must have a current rating of at least
390 mA. The capacitor selected in this design was a 4.7 μ F 50 V
capacitor with a 3 A current rating.
Step 8 Selecting input capacitor. The input capacitor must be
selected such that it provides a good filtering of the input voltage
waveform. To reduce the switching frequency noise, a good rule
of thumb is to set the input voltage high frequency ripple Δ V IN to
be 1% of the minimum input voltage. The minimum input capaci-
tor requirements are as follows:
the switching diode. In this design the PWM dimming frequency
is 200 Hz and the minimum duty cycle is 1%. Typically, the volt-
age variation on the output, V COUT , during PWM dimming must
be less than 250 mV, so that no audible hum can be heard. The
capacitance can be calculated as follows:
C IN =
=
8
8
? I Lused
f SW ? V IN
0.36 (A)
2 (MHz) 0.1 (V)
= 0.23 μ F
(26)
f PWM(dimming)
C OUT = I LK
1 – D (min)
V COUT
(24)
The rms current through the capacitor is given by:
= 200 μ A
1 – 0.01
200 Hz 0.250 V
= 3.96 μ F
C IN rms = ? I Lused / 12 = 0.104 A
(27)
A capacitor larger than 3.96 μ F should be selected due to degra-
dation of capacitance at high voltages on the capacitor. A ceramic
4.7 μ F 50 V capacitor is a good choice to fulfill this requirement.
Corresponding capacitors include:
A good ceramic input capacitor with ratings of 2.2 μ F 50 V or
4.7 μ F 50 V will suffice for this application. Corresponding
capacitors include:
Vendor
Murata
Murata
Value
4.7 μ F 50 V
2.2 μ F 50 V
Part number
GRM32ER71H475KA88L
GRM31CR71H225KA88L
Vendor
Murata
Murata
Value
4.7 μ F 50 V
2.2 μ F 50 V
Part number
GRM32ER71H475KA88L
GRM31CR71H225KA88L
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
28
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