S P 7 6 0 0
2 A 2 9 V N o n - S y n c . B u c k H i g h P o w e r L E D D r i v e r
Another benefit of using power sequencing for
power up is that it ensures all internal circuitry
is alive and fully operational before the device
is required to regulate the current through the
LEDs. Since the regulator was “Off” before
power was applied, it is unlikely the LED is
under any type of thermal stress. EXAR does
not recommend using the SP7600 in
applications where dimming of the LED is
achieved by PWM’ing the actual input power as
is common in automotive dimming
applications.
0 . 35 V ? ( 1 . 5 × 1 . 05 × I OCP × Rds ( on ))
33 μ A
Equ.3: L =
Fig. 17: LED Duty Cycle vs (1-D) DIM pin Duty Cycle
Vin=12V, 2 Luxeon K2 in Parallel with 2A total
M ODULATOR OPERATION AND POWER
SEQUENCING
The SP7600 has a unique modulator design
which improves the device’s ability to operate
at very high duty cycle. While seamless in
operation as the duty cycle is increasing (input
voltage falling), when the duty cycle is
decreased (input voltage rising), the user will
observe the switching frequency increasing in
distinct fractions of the switching frequency. If
the device is operating at 100% duty cycle, a
unique advantage of using a p-channel pass
device, and then the input voltage is
increased, the frequency will start at 300kHz,
then 600kHz, and then finally 1.2MHz. The
frequency will tend to increase to the next
higher fraction once the duty cycle reaches 75
to 65 percent. This is the normal operation of
the device and should be expected. There is
no impact on the LED current accuracy. If
PWM dimming is being used as the input
voltage is increased, one will see the
frequency increasing when the duty cycle is <
90%. When power is initially applied the
device will begin operating as if the input
voltage is increasing and may start operation
at one of the fractional operating frequencies.
Many users will prefer to have the device start
operating at the nominal operating frequency,
thus it is recommended that Vin be applied
after FB is set at the high state (>1.2V). The
regulator is now in standby and once Vin has
reached steady-state then FB is transitioned
from a high to a low state. The regulator then
starts operating at nominal frequency.
B UCK OPERATION WITHOUT OUTPUT
CAPACITOR
In order to be able to apply the
aforementioned dimming signal to the LED,
the output filter capacitor that is normally
used with a buck converter has to be removed
from the circuit. Thus the LED current ripple
equals the inductor current ripple. As a rule of
thumb current ripple should be limited to 30%
of ILED. Allowing for a higher current ripple,
up to 30%, while staying within LED
manufacturer ripple guidelines, will reduce
inductance and possibly inductor size.
O VERCURRENT PROGRAMMING
Resistor Rs can be used to program
Overcurrent Protection (OCP). Use the
following equation for calculating the Rs value.
Equ.2: Rs =
Where Iocp is the programmed overcurrent
and is generally set 50% above nominal
output current, and Rds(on) = 95mohms.
Maximum value of Rs that can be used for
programming OCP is 3k.
I NDUCTOR SELECTION
Select the inductor L1 for inductance, Irms
and Isat. Calculate inductance from
Vo × ( Vin ? Vo )
Vin × f × Δ I L
Where Vin is converter input voltage and Vo is
converter output voltage. Since voltage across
Rset is small, Vo approximately equals Vf (for
? 2009 Exar Corporation
9/13
Rev. 2.0.0
相关PDF资料
SPB2 PANEL SWING KIT
SPIKECUBE SURGE SUPPRESSR 1OUT DIRECT PLUG
SPIKESTIK SURGE SUPPRESSOR SPIKE STIK 6OUT
SPS-615-HG SURGE SUPP 6OUT 15'CORD HOSP GRD
SR202 SHELF FIXED 4-POST HEAVY DUTY
SR204 SHELF FIXED 2U CANTILEVER
SR205 SHELF SLIDING 4-POST 1U
SR206 SHELF SLIDING 4-POST 2U
相关代理商/技术参数
SP7600EN2-L/TR 功能描述:LED照明驱动器 2A 29V NON-SYNC BUCK HIGH PWR 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
SP7601 制造商:EXAR 制造商全称:EXAR 功能描述:29V High Voltage LED Driver
SP7601_EB 制造商:EXAR 制造商全称:EXAR 功能描述:29V High Voltage LED Driver
SP7601EB 功能描述:LED 照明开发工具 Eval Board for SP7601 Series 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:
SP7601EK1-L 功能描述:LED照明驱动器 High Curr DC-to-DC Buck LED Drvr 1.2MHz 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
SP7601EK1-L/TR 功能描述:LED照明驱动器 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
SP7606 制造商:EXAR 制造商全称:EXAR 功能描述:Wide Input Voltage Boost Controller
SP7606ER-L 制造商:EXAR 制造商全称:EXAR 功能描述:Wide Input Voltage Boost Controller