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| 型号： | ISL97686IRTZ-T |
| 厂商： | Intersil |
| 文件页数： | 10/23页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR BACKLIGHT 28TQFN |
| 标准包装： | 6,000 |
| 拓扑： | 线性（LDO），PWM，升压（升压） |
| 输出数： | 4 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 汽车，背光，通用型 |
| 频率： | 200kHz ~ 1.2MHz |
| 电源电压： | 9 V ~ 32 V |
| 输出电压： | 75V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-WFQFN 裸露焊盘 |
| 供应商设备封装： | 28-TQFN-EP（5x5） |
| 包装： | 带卷 (TR) |
| 工作温度： | -40°C ~ 105°C |
ISL97686
Theory of Operation
PWM Boost Converter
The current mode PWM boost converter produces the minimal
voltage needed to enable the LED string with the highest forward
voltage drop to run at the programmed current. The ISL97686
employs current mode control boost architecture that has a fast
current sense loop and a slow voltage feedback loop. The
number of LEDs that can be driven by ISL97686 depends on the
type of LED chosen in the application. The ISL97686 is capable
of boosting up to greater than 70V and driving 4 Channels of
LEDs at a maximum of 160mA per channel.
and absolute current accuracy. However, the absolute accuracy is
additionally determined by the external R ISET . A 0.1% tolerance
resistor is therefore recommended.
+
OVP and V OUT
+
-
REF
-
The Overvoltage Protection (OVP) pin has a function of setting the
overvoltage trip level as well as limiting the V OUT regulation range.
The ISL97686 OVP threshold is set by R UPPER and R LOWER as
shown in Equation 1:
RSET
PWM DIMMING
+
-
V OUT = -------------------------------------------------------------------------
1.21 ( R UPPER + R LOWER )
R LOWER
(EQ. 1)
FIGURE 16. SIMPLIFIED CURRENT SOURCE CIRCUIT
I LEDmax = -----------------
R ISET
and V OUT can only regulate between 30% and 100% of the
V OUT_OVP such that:
Allowable V OUT = 30% to 100% of V OUT_OVP
For example, a 1M ? R UPPER and 19k ? R LOWER sets OVP to 65.4V.
The boost can regulate down to 30% of OVP, so it can go as low
as 19.6V. If V OUT needs to be lower than this, the OVP level must
be reduced. Otherwise, V OUT will regulate to 19.6V, and the
ISL97686 may overheat. However, it’s recommended that the
OVP be set to no more than 20% above the nominal operating
voltage. This prevents the need for output capacitor voltage
ratings and the inductor current rating to be set significantly
higher than needed under normal conditions, allowing a smaller
and cheaper solution, as well as keeping the maximum voltages
and currents that can be seen in the system during fault
conditions at less extreme levels.
Parallel capacitors should be placed across the OVP resistors
such that R UPPER /R LOWER = C LOWER /C UPPER . Using a C UPPER
value of at least 30pF is recommended. These capacitors reduce
the AC impedance of the OVP node, which is important when
using high value resistors. The ratio of the OVP capacitors should
be the inverse of the OVP resistors. For example, if
R UPPER /R LOWER = 33/1, then C UPPER /C LOWER = 1/33 with
C UPPER = 100pF and C LOWER = 3.3nF. These components are not
always needed, but it is highly recommended to include
replacements to populate them if necessary.
Current Matching and Current Accuracy
The LED current in each channel is regulated using an active
current source circuit, as shown in Figure 16. The peak LED
current is set by translating the R ISET current to the output with a
scaling factor of 2919/R ISET . The drain terminals of the current
source MOSFETs are designed to run at 750mV to optimize
power loss versus accuracy requirements. The sources of
channel-to-channel current matching error come from the
op amp offsets, reference voltage, and current source sense
resistors. These parameters are optimized for current matching
10
Dynamic Headroom Control
The ISL97686 features a proprietary dynamic headroom control
circuit that detects the highest forward voltage string, or
effectively the lowest voltage from any of the CH pins. The
system will regulate the output voltage to the correct level to
allow the channel with the lowest voltage to have just sufficient
headroom to correctly regulate the LED current. Since all LED
strings are connected to the same output voltage, the other CH
pins will have a higher voltage, but the regulated current source
circuit on each channel will ensure that each channel has the
correct current level. The output voltage regulation is dynamic,
and is updated as needed, to allow for temperature and aging
affects in the LEDs.
Dimming Controls
The ISL97686 provides two basic ways to control the LED current,
and therefore, the brightness. These are described in detail in
subsequent sub-sections, but can be broadly divided into the
following two types of dimming:
Step 1. LED DC current adjustment
Step 2. PWM chopping of the LED current defined in Step 1.
LED DC Current Setting
The initial brightness should be set by choosing an appropriate
value for the resistor on the ISET1/2 pins. This resistor must
connect to AGND, and should be chosen to fix the maximum
possible LED current:
2919
(EQ. 2)
The ISL97686 includes two built-in levels of current, individually
set by the resistors on ISET1 and ISET2, according to Equation 2,
which can be switched between by using the CSEL pin.
CSEL = 0: The current setting is based on ISET1
CSEL = 1: The current setting is based on ISET2
FN7953.0
April 23, 2012
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相关代理商/技术参数 |
参数描述 |
|---|---|
| ISL97687IBZ | 功能描述:IC LED DRVR 4 CHAN PWM 28SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 恒定电流:- 恒定电压:- 拓扑:升压（升压），切换式电容器（充电泵） 输出数:1 内部驱动器:是 类型 - 主要:背光 类型 - 次要:白色 LED 频率:625kHz ~ 875kHz 电源电压:2.7 V ~ 5.3 V 输出电压:5V 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-µMAX 包装:带卷 (TR) 工作温度:-40°C ~ 85°C |
| ISL97687IBZEV1Z | 制造商:Intersil 功能描述:ISL97687 EVAL |
| ISL97687IBZ-T | 功能描述:IC LED DRVR 4 CHAN PWM 28SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 恒定电流:- 恒定电压:- 拓扑:升压（升压），切换式电容器（充电泵） 输出数:1 内部驱动器:是 类型 - 主要:背光 类型 - 次要:白色 LED 频率:625kHz ~ 875kHz 电源电压:2.7 V ~ 5.3 V 输出电压:5V 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-µMAX 包装:带卷 (TR) 工作温度:-40°C ~ 85°C |
| ISL97687IRTZ | 功能描述:IC LED DRVR 4 CHAN PWM 28TQFN RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 恒定电流:- 恒定电压:- 拓扑:升压（升压），切换式电容器（充电泵） 输出数:1 内部驱动器:是 类型 - 主要:背光 类型 - 次要:白色 LED 频率:625kHz ~ 875kHz 电源电压:2.7 V ~ 5.3 V 输出电压:5V 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-µMAX 包装:带卷 (TR) 工作温度:-40°C ~ 85°C |
| ISL97687IRTZ-T | 功能描述:IC LED DRVR 4 CHAN PWM 28TQFN RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 恒定电流:- 恒定电压:- 拓扑:升压（升压），切换式电容器（充电泵） 输出数:1 内部驱动器:是 类型 - 主要:背光 类型 - 次要:白色 LED 频率:625kHz ~ 875kHz 电源电压:2.7 V ~ 5.3 V 输出电压:5V 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-µMAX 包装:带卷 (TR) 工作温度:-40°C ~ 85°C |
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