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| 型号： | A8516ELPTR-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 11/17页 |
| 文件大小： | 0K |
| 描述： | IC LED DVR BACKLIGHT MON 24TSSOP |
| 标准包装： | 8,000 |
| 拓扑： | PWM，升压（升压） |
| 输出数： | 6 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 背光 |
| 类型 - 次要： | RGB，白色 LED |
| 频率： | 300kHz ~ 1MHz |
| 电源电压： | 8 V ~ 24 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 供应商设备封装： | 24-TSSOP 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 工作温度： | -40°C ~ 85°C |
A8516
LED Backlight Driver for LCD Monitors and Televisions
Functional Description
Overview The A8516 is a multi-output WLED/RGB control-
ler for backlighting medium-size displays. It has an integrated
gate driver for driving an external N-channel boost MOSFET.
The gate driver voltage is regulated at 7 V, which allows a wide
selection of power MOSFET (in contrast to being limited to
logic-level MOSFETs when using a 5 V gate driver). The boost
frequency, f SW . The value of f SW (MHz) is determined by:
f SW = 52 / R FSET ,
where f SW is in MHz and R FSET is in k Ω . The typical range of
R FSET is approximately 51 to 174 k Ω , which corresponds to
1 MHz to 300 kHz.
(4)
controller operates in fixed-frequency current-mode control. The
switching frequency can be set in the range from 300 kHz to
1 MHz, by an external resistor, R FSET , connected between FSET
and ground.
The external MOSFET switch is protected by pulse-by-pulse cur-
rent limiting. The current limit is independent of duty cycle, and
is set using an external sense resistor, R SC .
LED Current Setting The maximum LED current can be set, at
up to 130 mA/channel, through the ISET pin. Connect a resistor,
R ISET , between this pin and ground to set the reference current
level, I SET . The value of I SET (mA) is determined by:
Enable The IC turns on when a high signal is applied on the EN
pin, and turns off when this pin is pulled low. The LED current
sinks are turned on when both the EN and the PWM inputs are high.
Channel Selection The A8516 can be used to drive 1 to 6 LED
channels. During startup, the IC detects LED sink pins which are
shorted to ground, and disables the corresponding LED channel.
Therefore, any unused LED pins must be connected to ground,
otherwise the IC will go into overvoltage protection fault during
startup. LED pins can be paralleled together for higher cur-
rent. For example for a 3 parallel string configuration, connect
LED1-2, LED3-4, and LED5-6 together to deliver up to twice the
current per LED.
I SET = 1.235 / R ISET (k Ω ) .
(1)
PWM Dimming The A8516 has a very wide range for PWM
The resulting current is multiplied internally with a gain of 640
and mirrored on all enabled LEDx pins:
I LED = I SET × 640 . (2)
This sets the maximum current through each LEDx, referred as
the 100% Current . The LEDx current can be reduced from the
100% Current value by applying an external PWM signal on the
PWM pin. Conversely, we can calculate R ISET according to the
LED current required:
R ISET = ( 1.235 / I LED ) × 640 . (3)
In steady-state operation, the maximum average LED current that
can be handled by the IC depends on its thermal budget. That
is, maximum power dissipation and acceptable temperature rise.
signal input. It can accept a PWM signal from 100 Hz to 5 kHz.
When a PWM high signal is applied, the LEDx pins sink
100% Current. When the PWM signal is low, the LED sinks
turn off.
Referring to figure 13, there is a ramp-up delay between when
the PWM signal is applied and when the current reaches the
90% level. To improve current dimming linearity for PWM pulse
widths less than 100 μ s, increase the applied PWM pulse-width
by 3 to 5 μ s to compensate for this delay.
PWM
The thermal budget is affected by various parameters, such as
PCB size, copper plane around IC, LED V f mismatch, selection
of power components (MOSFET, inductor and diode), maximum
board temperature, and so on.
I LED
t D
Boost Switching Frequency Setting Connect an external
resistor between the FSET pin and GND, to set boost switching
Figure 13. Propagation delay from the PWM signal rising edge to I LEDx
reaching the 90% level
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
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