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| 型号： | A8514KLPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 30/42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
Design Example for SEPIC Configuration
Wide Input Voltage Range, High Efficiency
Fault Tolerant LED Driver
A8514 is 700 mV. A constant term, 2 V, is added to give margin
This section provides a method for selecting component values
to the design due to noise and output voltage ripple.
when designing an application using the A8514 in SEPIC (Sin-
gle-Ended Primary-Inductor Converter) circuit. SEPIC topology
has the advantage that it can generate a positive output voltage
either higher or lower than the input voltage. The resulting design
is diagrammed in figure 35.
V OUT(OVP) = # SERIESLEDS × V f + V LED + 2 (V)
= 4 × 3.3 (V) + 0.7 (V) + 2 (V) = 15.9 V
Then the OVP resistor is:
R OVP = ( V OUT(OVP) – V OVP(th) ) / I OVPH
(34)
(35)
Assumptions: For the purposes of this example, the following are
given as the application requirements:
? V BAT : 6 to 14 V ( V IN (min): 5 V and V IN (max): 16 V )
? Quantity of LED channels, # CHANNELS : 4
? Quantity of series LEDs per channel, # SERIESLEDS : 4
? LED current per channel, I LED : 60 mA
? LED V f at 60 mA: ≈ 3.3 V
? f SW : 2 MHz
= (15.9 (V) – 8.1 (V)) / 0.199 (mA) = 39.196 k Ω
where both I OVPH and V OVP(th) are taken from the Electrical
Characteristics table.
In this case a value of 39.2 k Ω was selected. Below is the actual
value of the minimum OVP trip level with the selected resistor:
V OUT(OVP) = 39.2 (k Ω ) × 0.199 (mA) + 8.1 (V) = 15.9 V
Step 3b At this point a quick check must be done to determine if
the conversion ratio is acceptable for the selected frequency.
? T A (max): 65°C
? PWM dimming frequency: 200 Hz, 1% duty cycle
D max = 1 – t SWOFFTIME × f SW
= 1 – 68 (ns) × 2 (MHz) = 86.4%
(36)
Procedure: The procedure consists of selecting the appropriate
configuration and then the individual component values, in an
ordered sequence.
where the minimum off-time (t SWOFFTIME ) is found in the Electri-
cal Characteristics table.
The Theoretical Maximum V OUT is then calculated as:
Step 1 Connecting LEDs to LEDx pins. If only some of the LED
channels are needed, the unused LEDx pins should be pulled to
ground using a 1.5 k Ω resistor.
V OUT (max) = V IN (min)
D max
1 – D max
– V d
(37)
Step 2 Determining the LED current setting resistor R ISET :
R ISET = ( V ISET × A ISET ) / I LED
(33)
= 5 (V)
0.86
1 – 0.86
– 0.4 (V) = 30.3 V
= (1.003 (V) × 653) / 0.60 (A) = 10.92 k Ω
Choose an 11.00 k Ω 1% resistor.
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. The regulation voltage, V LED , of the
where V d is the diode forward voltage.
The Theoretical Maximum V OUT value must be greater than
the value V OUT(OVP) . If this is not the case, it may be necessary
to reduce the frequency to allow the boost to convert the volt-
age ratios.
Step 4 Selecting the inductor. The inductor must be chosen such
that it can handle the necessary input current. In most applica-
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
30
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