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| 型号： | A8511KLPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 17/24页 |
| 文件大小： | 0K |
| 描述： | IC LED DVR 150MA AUTO 28-TSSOP |
| 标准包装： | 1 |
| 拓扑： | PWM，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： | 高亮度 LED（HBLED），RGB，白色 LED |
| 频率： | 600kHz ~ 2.1MHz |
| 电源电压： | 8 V ~ 21 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SOIC（0.173"，4.40mm 宽）裸露焊盘 |
| 供应商设备封装： | 28-TSSOP 裸露焊盘 |
| 包装： | 标准包装 |
| 工作温度： | -40°C ~ 125°C |
| 其它名称： | 620-1367-6 |
A8511
LED Current Setting
2 MHz, 4 Channel×150 mA WLED/RGB Driver
With Output Disconnect
LED Open Detect When any LED string opens, the boost
The maximum LED current can be up to 150 mA per chan-
nel, and is set through the ISET pin. Connect a resistor, RISET,
between this pin and AGND to set the reference current level,
I ISET , according to the following formula:
I ISET = 1.235 / R ISET , (2)
where I ISET is in mA and R ISET is in k Ω .
This current is multiplied internally with a gain of 960, and mir-
rored on all enabled LED pins. This sets the maximum current
through the LEDs, referred as the 100% current .
Dimming The LED current can be reduced from the 100% cur-
rent level by three alternative dimming methods:
? PWM dimming using the EN pin. PWM dimming is performed
by applying an external PWM signal on the EN pin. When
the EN pin is pulled high, the A8511 turns on and all enabled
LEDs sink 100% current. The sequence is shown in figure 2.
For optimal accuracy, the external PWM signal should be in the
range 100 to 300 Hz. The slight delay between PWM signal and
the LED current causes an error. To compensate for the error,
a small turn-on delay should be added to the PWM signal as
shown on page 10 of the Performance Characteristics section.
When EN is pulled low, the boost converter and LED sinks are
turned off. The compensation (COMP) pin is floated, and criti-
circuit increases the output voltage until it reaches the overvolt-
age protection level. The OVP event causes any LED string that
is not in regulation to be locked-out from regulating the loop. By
removing the open LED from controlling the boost, the output
voltage returns to normal operating voltage. Every OVP event
retests all LED strings. An EN low signal does not reset the LED
string regulation lock unless it shuts down the device (exceeds
t PWML ). The locked-out LED pins always attempt to sink desired
current regardless of lock-out state.
LED Short Detect Any LED pin that has a voltage exceed-
ing V LEDSC will force the device to disable the boost circuit and
LEDx outputs until EN shuts down the A8511 (EN low exceeds
t PWML ). This protects the LEDx pins from potentially hazardous
voltages when multiple LEDs are shorted in one string.
Overvoltage Protection The A8511 has overvoltage protec-
tion (OVP) and open Schottky diode protection.
The OVP has a default level of 19.5 V and can be increased up to
38 V by the selection of an external resistor, as shown in figure 3.
When the current though OVP pin exceeds 200 μ A, the OVP
comparator goes low. When V OUT falls and current through the
OVP pin drops below 165 μ A, the OVP is released.
cal internal circuits are kept active. If EN is pulled low for more
than t PWML , the device enters shutdown mode and clears all
internal fault registers. As an example, for a 2 MHz clock, the
maximum PWM low period while avoiding shutdown is 65 ms.
? Analog dimming using the DIM pin. When the DIM pin is
pulled low, the LED sinks draw 100 % current; when the pin is
pulled high, the LED current level drops to 25%.
? Analog dimming using the VTI pin. External DC voltage can be
applied to the VTI pin to control LED current. LED current var-
ies as a function of voltage on the VTI pin. This configuration is
shown in figure 5.
V BATT
A8511
Latch
SW SW SW
–
+
1.23 V
18 V
D1
ROVP
OVP
V OUT
COUT
–
+
EN
I LEDX
External PWM Signal
Turn-on delay
100% Current
0 mA
OVP
Disable
1.23 V
Figure 2. Timing diagram of external PWM signal and LED current
Figure 3. Overvoltage protection (OVP) circuit
8511-DS
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
17
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