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| 型号： | A8502KLPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 30/35页 |
| 文件大小： | 0K |
| 描述： | IC LED DVR WHITE MULTI 16-TSSOP |
| 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： | 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： | 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 ~ 125°C |
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A8502
Design Example for SEPIC Configuration
Wide Input Voltage Range, High Efficiency
Fault Tolerant LED Driver
Step 3a The first step is determining the maximum voltage based
This section provides a method for selecting component values
when designing an application using the A8502 in SEPIC (Sin-
gle-Ended Primary-Inductor Converter) circuit. SEPIC topology
on the LED requirements. The regulation voltage, V LED , of the
A8502 is 720 mV. A constant term, 2 V, is added to give margin
to the design due to noise and output voltage ripple.
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 34.
Assumptions: For the purposes of this example, the following are
given as the application requirements:
V OUT(OVP) = # SERIESLEDS × V f + V LED + 2 (V)
= 4 × 3.2 (V) + 0.720 (V) + 2 (V) = 15.9 V
Then the OVP resistor is:
R OVP = ( V OUT(OVP) – V OVP(th) ) / I OVPH
(31)
(32)
? V BAT : 6 to 14 V ( V IN (min): 5 V and V IN (max): 16 V )
? Quantity of LED channels, # CHANNELS : 2
? Quantity of series LEDs per channel, # SERIESLEDS : 4
? LED current per channel, I LED : 120 mA
? LED V f at 120 mA: ≈ 3.3 V
? f SW : 2 MHz
? T A (max): 65°C
? PWM dimming frequency: 200 Hz, 1% duty cycle
= (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.
Procedure: The procedure consists of selecting the appropriate
D max = 1 – t SWOFFTIME × f SW
(33)
configuration and then the individual component values, in an
ordered sequence.
Step 1 Connect LEDs to pins LED1 and LED2. Note: if only one
LED channel is needed, the unused LEDx pin should be pulled to
ground using a 1.5 k Ω resistor. Alternatively, short the LED1 and
= 1 – 68 (ns) × 2 (MHz) = 86.4%
where the minimum off-time (t SWOFFTIME ) is found in the Electri-
cal Characteristics table.
The Theoretical Maximum V OUT is then calculated as:
– 0.4 (V) = 30.3 V
LED2 pins together, and half the LED current, to 60 mA
per channel.
Step 2 Determining the LED current setting resistor R ISET :
R ISET = ( V ISET × A ISET ) / I LED
(30)
V OUT (max) = V IN (min)
= 5 (V)
D max
1 – D max
0.86
1 – 0.86
– V d
(34)
= (1.003 (V) × 980) / 120 mA = 8.19 k Ω
Choose a 8.25 k Ω resistor 1% resistor (or 16.2 k Ω if I LED is
60mA/channel).
Step 3 Determining the OVP resistor. The OVP resistor is
connected between the OVP pin and the output voltage of the
converter.
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, the switching frequency
of the boost converter must be reduced to meet the maximum
duty cycle requirements.
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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