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| 型号： | A8515GLPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 25/34页 |
| 文件大小： | 0K |
| 描述： | IC LED DVR WHT/RGB BKLGT 16TSSOP |
| 标准包装： | 8,000 |
| 拓扑： | PWM，升压（升压） |
| 输出数： | 2 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 背光 |
| 类型 - 次要： | 白色 LED |
| 频率： | 600kHz ~ 2.5MHz |
| 电源电压： | 5 V ~ 40 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 供应商设备封装： | 16-TSSOP-EP |
| 包装： | 带卷 (TR) |
| 工作温度： | -40°C ~ 105°C |
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A8515
Design Example for Boost Configuration
Wide Input Voltage Range, High Efficiency
Fault Tolerant LED Driver
Applications Information
Then the OVP resistor is:
This section provides a method for selecting component values
R OVP = ( V OUT(OVP) – V OVP(th) ) / I OVPH
(9)
when designing an application using the A8515. The resulting
design is diagramed in figure 32.
Assumptions: For the purposes of this example, the following are
given as the application requirements:
? V BAT : 10 to 14 V
? Quantity of LED channels, # CHANNELS : 2
? Quantity of series LEDs per channel, # SERIESLEDS : 10
? LED current per channel, I LED : 120 mA
? V f at 120 mA: 3 to 3.6 V
? f SW : 2 MHz
= (38.72 V – 8.1 V) / 199 μ A = 154 k Ω
where both I OVPH and V OVP(th) are taken from the Electrical
Characteristics table.
Chose a value of resistor that is higher value than the calculated
R OVP . In this case a value of 158 k Ω was selected. Below is the
actual value of the minimum OVP trip level with the selected
resistor:
V OUT(OVP) = 158 k Ω × 199 μ A + 8.1 V = 39.5 V
Step 3b At this point a quick check must be done to see if the
conversion ratio is acceptable for the selected frequency.
? T A (max): 65°C
? PWM dimming frequency: 200 Hz, 1% Duty cycle
D maxofboost = 1 – t SWOFFTIME × f SW
= 1 – 1.5 × 47 ns × 2 MHz = 85.9%
(10)
Procedure: The procedure consists of selecting the appropriate
configuration and then the individual component values, in an
ordered sequence.
where minimum off time (t SWOFFTIME ) is found in the Electrical
Characteristics table.
The Theoretical Maximum V OUT is then calculated as:
V IN (min)
1 – D maxofboost
– 0.4 = 70.5 V
Step 1 Connect LEDs to pins LED1 and LED2.
Step 2 Determining the LED current setting resistor R ISET :
R ISET = 1.003 × 980 / I LED
= 983 / 120 mA = 8.19 k Ω
Choose a 8.25 k Ω resistor.
(7)
V OUTthe (max) =
=
10 V
1 – 0.859
– V d
(11)
Step 3 Determining the OVP resistor. The OVP resistor is
connected between the OVP pin and the output voltage of the
converter.
Step 3a The first step is determining the maximum voltage
based on the LED requirements. Then this value and the regula-
tion voltage (V LED ) should be added together, as well as another
2 V to take noise and output ripple into consideration. The V LED
of the A8515 is 720 mV.
where V d is the diode forward voltage. A good approximation of
efficiency η can be taken from the efficiency curves located in
this datasheet. A value of 90% is a good starting approximation.
The Theoretical Maximum V OUT value must be greater than the
value V OUT(OVP) . If this is not the case, the switching frequency
of the boost converter must be reduced to meet the maximum
duty cycle requirements.
Step 4 Selecting the inductor. The inductor must be chosen such
V OUT(OVP) = # SERIESLEDS × V f + V LED + 2
= 10 × 3.6 V+ 2.0 V + 0.720 V
= 38.72 V
(8)
that it can handle the necessary input current. In most applica-
tions, due to stringent EMI requirements, the system must operate
in continuous conduction mode throughout the whole input volt-
age range.
25
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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