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ISL97632
Applications
Efficiency Improvement
Figure 2 on page 5 shows the efficiency measurements. The
choice of the inductor has a significant impact on the power
efficiency. As shown in Equation 4, the higher the
inductance, the lower the peak current therefore the lower
the conduction and switching losses. On the other hand, it
has also a higher series resistance. Nevertheless, the
efficiency improvement from lowering the peak current is
greater than the impact of the resistance increase with larger
value of inductor. Efficiency can also be improved for
systems that have high supply voltages. Since the ISL97632
can only supply from 2.4V to 5.5V, V IN must be separated
from the high supply voltage for the boost circuit as shown in
Figure 7 and the efficiency improvement is shown in
Figure 8.
the ISL97632 is not sufficient. However, the ISL97632 can
be used as an LED controller with an external protection
MOSFET connected in cascode fashion to achieve higher
output voltage. A conceptual 9 LEDs driver circuit is shown
in Figure 9. A 40V logic level N-Channel MOSFET is
configured such that its drain ties between the inductor and
the anode of Schottky diode, its gate ties to the input, and its
source ties to the ISL97632 LX node connecting to the drain
of the internal switch. When the internal switch turns on, it
pulls the source of M1 down to ground, and LX conducts as
normal. When the internal switch turns off, the source of M1
will be pulled up by the follower action of M1, limiting the
maximum voltage on the ISL97632 LX pin to below V IN , but
allowing the output voltage to go much higher than the
breakdown limit on the LX pin. The switch current limit and
maximum duty cycle will not be changed by this setup, so
input voltage will need to be carefully considered to make
sure that the required output voltage and current levels are
C3 0.22μF
D1
achievable. Because the source of M1 is effectively floating
when the internal LX switch is off, the drain-to-source
Vs = 12V
C1
1μF
1
L1
22μH
2
D2
D3
capacitance of M1 may be sufficient to capacitively pull the
node high enough to breaks down the gate oxide of M1. To
prevent this, V OUT should be connected to V IN , allowing the
internal Schottky to limit the peak voltage. This will also hold
EN
V IN = 2.7V TO 5.5V
C2 0.1μF
VIN LX
VOUT
ISL97632
FBSW
FB
D4 25mA
D5
D6
the V OUT pin at a known low voltage, preventing the built in
OVP function from causing problems. This OVP function is
effectively useless in this mode as the real output voltage is
outside its intended range. If the user wants to implement
their own OVP protection (to prevent damage to the output
SDIN
GND
R1
4 Ω
capacitor, they should insert a zener from V OUT to the FB
pin. In this setup, it would be wise not to use the FBSW to FB
switch as otherwise the zener will have to be a high power
one capable of dissipating the entire LED load power. Then
FIGURE 7. SEPARATE HIGH INPUT VOLTAGE FOR HIGHER
EFFICIENCY OPERATION
the LED stack can then be connected directly to the sense
resistor and via a 10k resistor to FB. A zener can be placed
from V OUT to the FB pin allowing an over voltage event to
pull up on FB with a low breakdown current (and thus low
90
V S = 12V
power zener) as a result of the 10k resistor.
85
V S = 9V
V IN = 2.7V TO 5.5V
1
L1
2
D0
80
C1
1μF
2.2μH
M1
10BQ100
C3
4.7μF
D1
FQT13N06L
D2
75
70
0
5
10
15 20
ILED (mA)
V IN = 4V
6 LEDs
L1 = 22μH
R1 = 4 Ω
25
30
C2
0.1μF
VIN VOUT
LX
ISL97632
FBSW
EN
FB
SDIN
GND
R1
SK011C226KAR
6.3 Ω
FIGURE 8. EFFICIENCY IMPROVEMENT WITH 9V AND 12V
INPUTS
D8
D9
9 LEDs Operation
For medium size LCDs that need more than 7 low power
LEDs for backlighting, such as a Portable Media Player or
Automotive Navigation Panel displays, the voltage range of
7
FIGURE 9. CONCEPTUAL 9 LEDS HIGH VOLTAGE DRIVER
FN9239.3
March 22, 2010
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相关代理商/技术参数
ISL97634ART26Z-TK 制造商:Intersil Corporation 功能描述:
ISL97634IRT14Z 制造商:Intersil 功能描述:White LED Driver with PWM Dimming(3 LED)
ISL97634IRT14Z-T 功能描述:IC LED DRIVR WHITE BCKLGT 8-TDFN 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
ISL97634IRT14Z-TK 功能描述:IC LED DRIVR WHITE BCKLGT 8-TDFN 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
ISL97634IRT18Z 制造商:Intersil 功能描述:White LED Driver with PWM Dimming(4 LED)
ISL97634IRT18Z-T 功能描述:IC LED DRIVR WHITE BCKLGT 8-TDFN 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
ISL97634IRT18Z-TK 功能描述:IC LED DRIVR WHITE BCKLGT 8-TDFN 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
ISL97634IRT26Z-T 功能描述:IC LED DRIVR WHITE BCKLGT 8-TDFN 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