收藏本站
Micrel, Inc.
Maximum Power dissipated in R CS is;
Input Capacitor
MIC3230/1/2
P R CS = I R CS _ RMS × R CS
Eq. (17)
2
The input current is shown in Figure 5. For superior
performance, ceramic capacitors should be used because of
Eq. (18)
I R CS _ RMS _ max = I FET _ RMS _ max = D ? ? I IN _ AVE _ max 2 +
0 . 26 2 ? ?
I R CS _ RMS = 0 . 78 ? 1 . 64 2 +
?
12 ? ?
?
?
?
?
?
= 1 . 44 A _ rms
?
P R CS = 1 . 25 2 × . 15 = 0 . 31 watt
I L _ PP 2 ? ?
12
their low equivalent series resistance (ESR). The input ripple
current is equal to the ripple in the inductor plus the ripple
voltage across the input capacitor, which is the ESR of C IN
times the inductor ripple. The input capacitor will also
bypass the EMI generated by the converter as well as any
voltage spikes generated by the inductance of the input line.
For a required V IN_RIPPLE :
Eq. (21)
Use a 1/2 Watt resistor for R CS .
Output Capacitor
C IN =
I IN _ PP
8 × V IN _ RIPPLE × F SW
=
( 0 . 28 A )
8 × 50 mV × 500 kHz
= 1 . 4 μ F
ILED nom * D nom * T
In this LED driver application, the ILED ripple current is a
more important factor compared to that of the output
ripple voltage (although the two are directly related). To
find the C OUT for a required ILED ripple use the following
calculation:
For an output ripple ILED ripple = 20% of ILED nom
ILED ripple = 0 . 2 × 0 . 35 = 70 mA
Eq. (19) C out =
ILED ripple * ( R adj + R LED _ total )
Find the equivalent ac resistance R LED _ ac from the
datasheet of the LED. This is the inverse slope of the
ILED vs. V F curve i.e.:
This is the minimum value that should be used. The input
capacitor should also be rated for the maximum RMS input
current. To protect the IC from inductive spikes or any
overshoot, a larger value of input capacitance may be
required and it is recommended that ceramic capacitors be
used. In this design example a value of 4.7μF ceramic
capacitor was selected.
MOSFET Selection
In this design example, the FET has to hold off an output
voltage maximum of 30V. It is recommended to use an 80%
de-rating value on switching FETs, so a minimum of a 38V
FET should be selected. In this design example, a 75V FET
has been selected.
The switching FET power losses are the sum of the
Eq. (20)
R LED _ ac =
Δ V F
Δ ILED
conduction loss and the switching loss:
Eq. (22) P FET = P FET _ COND + P FET _ SWITCH
C out =
ILED nom * D nom * T
? I L _ PP ?
= D ? I IN _ AVE +
?
I FET _ RMS
12 ? ?
?
T =
Eq. (24)
In this example, use R LED _ ac = 0 . 1 ? for each LED.
If the LEDs are connected in series, multiply
R LED _ ac = 0 . 1 ? by the total number of LEDs. In this
example of 6 LEDs, we obtain the following:
R LED _ total = 6 × 0 . 1 Ω = 0 . 6 Ω
= 4 . 1 uF
ILED ripple * ( R adj + R LED _ total )
Use the next highest standard value, which is 4.7 μ F.
There is a trade off between the output ripple and the
rising edge of the PWMD pulse. This is because
between PWM dimming pulses, the converter stops
pulsing and C OUT will start to discharge. The amount that
C OUT will discharge depends on the time between PWM
Dimming pluses. At the next PWMD pulse C OUT has to
be charged up to the full output voltage V OUT before the
desired LED current flows.
The conduction loss of the FET is when the FET is turned
on. The conduction power loss of the FET is found by the
following equation:
Eq. (23) P FET _ COND = I FET _ RMS 2 × R DSON , where
2
2
?
The switching losses occur during the switching transitions
of the FET. The transition times, t transition , are the times when
the FET is turning off and on. There are two transition times
per period, T. It is important not to confuse T (the period)
with the transition time, t transition .
1
Fsw
Eq. (25)
P FET _ SWITCH _ max = I FET _ AVE _ max × V OUT _ max × t transition _ max × F SW
To find t transition _ max :
March 2011
15
M9999-030311-D
发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

*型号 *数量 厂商 批号 封装
添加更多采购

我的联系方式

*
*
*
相关PDF资料
MIC3263YML TR IC LED DRIVER 6CH BKLT 24-MLF
MIC3287-24YD6 TR IC LED DRIVR WHITE BCKLGT TSOT-6
MIC3289-16YD6 TR IC LED DRIVR WHITE BCKLGT TSOT-6
MIC3291-18YML TR IC PWM WLED DVR 1.8V 1.2MHZ 8MLF
MIC4100YM IC DRIVER MOSFET 100V CMOS 8SOIC
MIC4102YM IC DRIVER MOSFET 100V TTL 8SOIC
MIC4103YM IC MOSFET DRIVER 100V CMOS 8SOIC
MIC4124YME IC MOSFET DRVR DUAL NONINV 8SOIC
相关代理商/技术参数
MIC3231YTSE TR 功能描述:LED照明驱动器 Boost Driver Controller with Dither for High Power LEDs RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MIC3232YMM 功能描述:LED照明驱动器 400kHz Fixed Frequency Boost Driver Controller for High Power LEDs RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MIC3232YMM EV 功能描述:LED 照明开发工具 400kHz Fixed Frequency Boost Driver Controller for High Power LEDs - Evaluation Board RoHS:否 制造商:Fairchild Semiconductor 产品:Evaluation Kits 用于:FL7732 核心: 电源电压:120V 系列: 封装:
MIC3232YMM TR 功能描述:LED照明驱动器 400kHz Fixed Frequency Boost Driver Controller for High Power LEDs RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MIC3263 制造商:MICREL 制造商全称:Micrel Semiconductor 功能描述:Six-Channel WLED Driver for Backlighting Applications with Flicker-Free Dimming
MIC3263YML 制造商:Micrel 功能描述:6 Channel WLED Driver for Backlighting
MIC3263YML EV 制造商:Micrel Inc 功能描述:
MIC3263YML TR 功能描述:LED照明驱动器 Six Channel WLED Driver for Backlighting Applications RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N