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| 型号： | A8511KLPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 21/24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
Set inductor ripple at 30% of I BAT (max):
2 MHz, 4 Channel×150 mA WLED/RGB Driver
With Output Disconnect
8. Select input capacitor CIN, given:
I L = I BAT (max) × I Lripple (Ideal) .
(14)
C IN = ? I L / (8 × f SW × ? V INripple ) ,
(22)
Substituting:
? I L = 0.3 × 963 = 289 mA .
Given, during switch on-time:
where ? V INripple is the input ripple voltage, which can be as-
sumed to be 1% of V BAT . Then:
C IN = 0.3 / (8 × 2 × 10 6 × 0.01 × 8) = 0.23 μ F .
V BAT (min) = L × ? I L × f SW / D ,
(15)
Select a 2.2 μ F or higher, 35 or 50 V, ceramic capacitor, X5R
8 = L × 0.289 × 2
×10 6
/ 0.75, and
or X7R grade.
L = 10.4 μ H .
Select a common value: L (used) = 10 μ H.
It is recommended to select an inductor that can handle a DC
current level that is greater than 963 mA, at the peak current
The RMS current through CIN is given by:
I INRMS = ( I OUT × r ) / [(1 – D ) × 12 1/2 ],
= [(80 mA × 3 )× 0.3]
/ [(1 – 0.75) × 3.46] = 83 mA .
(23)
level (saturation) of 963 mA + 289 mA / 2 = 1.11 A. This is
to ensure that the inductor does not saturate at any steady
state or transient condition, within specified temperature and
tolerance ranges. Inductor saturation level decreases with
increasing temperature. It is advisable to use a inductor with a
saturation level of 2.0 A. The inductor should have a low DC
resistance (DCR) and core loss for better efficiency.
7. Select output capacitor COUT, given:
f PWM = 100 Hz , (16)
assuming 20% minimum dimming PWM duty cycle,
D PWM(min) , and the maximum leakage current through the
output disconnect switch at V OUT = 28 V is 165 μ A and
V COUTripple = 0.25 V.
Select the output capacitor as:
C OUT = I lk × (1 – D PWM(min) ) / ( f PWM × V COUTripple ) . (17)
Substituting:
Select a capacitor with an RMS current rating greater
than 83 mA.
9. Select the boost diode D1 (connect between the SW pins and
the output). D1 should be a Schottky diode with low forward
drop and junction capacitance.
The diode reverse voltage rating should be greater than V OUT .
A 40 to 50 V diode rating is recommended.
The diode DC current rating should be greater than I OUT and
the peak repetitive current rating should be > I BAT (max)
+ ? I L / 2.
10. Select the compensation capacitor CCOMP (connect between
the COMP pin and ground). Typically, use a 1 μ F capacitor to
reduce audio hum during PWM dimming.
11. Calculate Power Loss. Calculate power loss at various operat-
ing conditions to estimate worst-case power dissipation.
a) Loss in LED drive:
C OUT = 165 μ A× (1 – 0.2) / (100 × 0.25) = 5.3 μ F .
Select 6.8 μ F.
(18)
I LEDx × V LEDx for one string
+ ( I LEDx × V LEDx (av) +0.75
The RMS current through COUT is given by:
× quantity of remaining enabled LED strings),
(24)
C rms = I OUT × ? ?
? D (max) + ( r / 12) ? 1 / 2
?
?
?
?
1– D
,
(19)
where V LEDx is the regulation voltage of the LEDx pins, 0.75 V
typical, and worst-case drop is mismatch due to LED V f .
where:
r = Δ I L / I BAT (max)
, and
(20)
A good approximation for V LEDx (av) is 0.8 V. This assumes
that some of the remaining strings will regulate below, and
some above, a value of 1.55 V. If the predicted LED match-
? I L = ? ?
? V BAT (min) × D
L (used) × f SW
?
?
Substituting:
?
?
?
?
.
(21)
ing is tighter, then a lower value can be used. If the predicted
LED mismatch is large, then a higher value should be used.
To get the complete and accurate power dissipation, the user
will need to measure each individual LED pin to get the exact
(80 mA × 3 )× {[0.75 + (0.3 / 12)]/(1–0.75)} 1/2 = 0.422 A .
Select a capacitor with an RMS current rating greater than 0.422 A.
V LED voltage:
(80 mA × 0.75) + [80 mA × 2 × (0.8 + 0.75)] = 0.308 W .
8511-DS
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
21
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