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参数资料
| 型号： | A8511KLPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 19/24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
Bias Supply
2 MHz, 4 Channel×150 mA WLED/RGB Driver
With Output Disconnect
Audible noise can be minimized with higher dimming frequency,
The BIAS pin provides regulated 6 V for internal circuits. Con-
nect a CBIAS capacitor with a value in the range of 0.1 to 1 μ F.
Efficiency Considerations
For better efficiency, use a high quality inductor with relatively
low DCR and core loss.
Use a low forward voltage Schottky diode with relatively low
junction capacitance.
Use matched forward voltage LEDs for better efficiency.
The A8511 provides an output disconnect function through a load
but at higher dimming frequencies accuracy may be affected, as
shown in the Performance Characteristics section. It is recom-
mended to use 200 Hz for optimum performance.
Selecting a sufficiently large capacitor across the boost output can
reduce voltage ripple and noise. It is observed that the audible
noise below 250 mV ripple is negligible.
The value to select for a boost capacitor can be calculated using
the following formula:
switch that is connected from the boost converter output (CAP) to
LED connection (OUT). This function protects the system against
short circuit conditions from common anode LED connection to
C ≥
I lk
(1 – D FPWMmin )
f PWM 0.25
.
(5)
ground, for both boost and SEPIC configurations.
When comparing the efficiency of the A8511 with an alternate
implementation requiring an external input/output disconnect
function, the additional power dissipation in this disconnect
switch must be considered for a proper comparison. To bypass
the disconnect switch, short the CAP pin to the OUT pin to
have a direct connection from the boost regulator to the com-
mon anode LED node. When the disconnect switch is bypassed,
both the boost and the SEPIC implementations are not protected
against output short circuit conditions.
Audible Noise Considerations
where
I lk is the leakage current; select I lk = 165 μ A at a 30 V output and
175 μ A at a 40 V output,
D FPWMmin is the minimum dimming PWM duty cycle, and
f PWM is the dimming frequency; typically 200 Hz.
For example, if the dimming frequency is 200 Hz, the minimum
dimming PWM duty cycle = 10%, and V OUT = 30 V, then select
the boost capacitor as:
Multilayer ceramic capacitors cause audible noise when sub-
jected to voltage ripple in the audio frequency range, due to the
C =
165 μ A (1 – 0.1)
200 0.25
= 3 μ F
.
piezoelectric effect. Ceramic capacitors connected across boost
converters can also cause audible noise due to voltage ripple
at dimming frequencies. During the PWM dimming off-time,
the voltage across the capacitors drops due to leakage through
the output disconnect switch and the OVP pin. This voltage is
regulated to the desired output level during the PWM dimming
on-time. This voltage ripple may cause audible noise.
The capacitance of ceramic capacitors drops with DC bias. Use
an appropriate capacitor to get at least 3 μ F at 30 V.
The selection of a ripple voltage of 0.25 V is based on a typical
MLCC. This ripple level depends on the type and construction of
the MLCC. Increase the boost capacitor if noise exists at 0.25 V.
8511-DS
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
19
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