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参数资料
| 型号： | A8514KLPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 11/42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
Functional Description
The A8514 incorporates a current-mode boost controller with
internal DMOS switch, and four LED current sinks. It can be
used to drive four LED strings of up to 12 white LEDs in series,
with current up to 80 mA per string. For optimal efficiency,
the output of the boost stage is adaptively adjusted to the mini-
mum voltage required to power all of the LED strings. This is
expressed by the following equation:
V OUT = max ( V LED1 ,..., V LED4 ) + V REG (1)
where
V LEDx is the voltage drop across LED strings 1 through 4, and
V REG is the regulation voltage of the LED current sinks (typi-
cally 0.7 V at the maximum LED current).
Powering up: LED pin short-to-ground check
The VIN pin has a UVLO function that prevents the A8514
from powering-up until the UVLO threshold is reached. After
the VIN pin goes above UVLO, and a high signal is present on
the PWM/EN pin, the IC proceeds to power-up. As shown in
figure 3, at this point the A8514 enables the disconnect switch
and checks if any LEDx pins are shorted to ground and/or are not
used.
The LED detect phase starts when the GATE voltage of the
disconnect switch is equal to V IN – 4.5 V. After the voltage
threshold on the LEDx pins exceeds 120 mV, a delay of between
3000 and 4000 clock cycles is used to determine the status of the
pins. Thus, the LED detection duration varies with the switching
frequency, as shown in the following table:
Enabling the IC
The IC turns on when a logic high signal is applied on the
PWM/EN pin with a minimum duration of t PWMH for the first
clock cycle, and the input voltage present on the VIN pin is
greater than the 4.35 V necessary to clear the UVLO (V UVLOrise )
threshold. The power-up sequence is shown in figure 2. Before
Switching Frequency
(MHz)
2
1
0.800
0.600
Detection Time
(ms)
1.5 to 2
3 to 4
3.75 to 5
5 to 6.7
the LEDs are enabled, the A8514 driver goes through a system
check to determine if there are any possible fault conditions that
The LED pin detection voltage thresholds are as follows:
might prevent the system from functioning correctly. Also, if the
FSET/SYNC pin is pulled low, the IC will not power-up. More
information on the FSET/SYNC pin can be found in the Sync
section of this datasheet.
LED Pin Voltage
<70 mV
150 mV
325 mV
LED Pin Status
Short-to-ground
Not used
LED pin in use
Action
Power-up is halted
LED removed from operation
None
C1
VDD
GATE
GATE = V IN – 4.5 V
FSET/SYNC
C1
LEDx
C2
ISET
C2
LED detection period
C3
PWM/EN
C3
ISET
C4
C4
PWM/EN
t
Figure 2. Power-up diagram; shows VDD (ch1, 2 V/div.), FSET/SYNC (ch2,
1 V/div.), ISET (ch3, 1 V/div.), and PWM/EN (ch4, 2 V/div.) pins,
time = 200 μ s/div.
t
Figure 3. Power-up diagram; shows the relationship of an LEDx pin with
respect to the gate voltage of the disconnect switch (if used) during the
LED detect phase, as well as the duration of the LED detect phase for a
switching frequency of 2 MHz; shows GATE (ch1, 5 V/div.), LED (ch2,
500 mV/div.), ISET (ch3, 1 V/div.), and PWM/EN (ch4, 5 V/div.) pins,
time = 500 μ s/div.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
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