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参数资料
| 型号： | MAX8879ETG+T |
| 厂商： | Maxim Integrated |
| 文件页数： | 9/16页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR WT/RGB BCKLGT 24TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 恒定电流： | 是 |
| 拓扑： | 切换式电容器（充电泵） |
| 输出数： | 11 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 背光 |
| 类型 - 次要： | RGB，白色 LED |
| 频率： | 1MHz |
| 电源电压： | 2.7 V ~ 5.5 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-WFQFN 裸露焊盘 |
| 供应商设备封装： | 24-TQFN-EP（4x4） |
| 包装： | 带卷 (TR) |
| 工作温度： | -40°C ~ 85°C |
Charge Pump for Backlight/Flash/RGB LEDs
with Safety Timer
Detailed Description
The MAX8879 charge pump operates in three modes to
maintain high efficiency over a wide supply voltage
range. The IC automatically selects between these
three modes as described in the 1x/1.5x/2x Mode
Switchover section.
Current-sinking LED cathode connections are provided
to drive four main (M_) and three sub (S_) LEDs at a
regulated current up to 30mA each. The sub LED con-
nections can be used for either subdisplay backlighting
or one RGB indicator. The IC also contains four flash
LED connections (F_) that sink up to 100mA each.
These LED connections can be connected together in
any combination to provide increased current up to
610mA total.
An I 2 C serial port is used for on/off control and setting
the LED currents in 32 linear steps. When using the
RGB indicator, the I 2 C port provides 32k colors and
programmable ramp-up/down rates. The camera flash
may be turned on/off through a separate digital logic
input ( FSH ) with the maximum flash safety timer pro-
grammed to an I 2 C-selectable value. The movie mode
may be turned on/off only though the I 2 C interface. The
flash and movie modes have separately adjustable
brightness levels through separate I 2 C registers.
1x/1.5x/2x Mode Switchover
When the input voltage is higher than the required out-
put voltage needed to drive the LEDs, the MAX8879
pulls OUT up to the input voltage (in 1x mode), while
still regulating the LED current with the current regula-
tors. As the input voltage drops, the lowest LED cath-
ode voltage falls below the 100mV switchover
threshold, and the MAX8879 starts switching in 1.5x
mode. When the input voltage is rising, the transition
from 1.5x to 1x is made when V IN is greater than V OUT .
When the MAX8879 is running in 1.5x mode and the
input voltage is decreased, the lowest LED cathode
voltage crosses the 100mV switchover threshold again.
At this point, the MAX8879 changes to the 2x charge-
pump mode. With the input voltage rising and the
MAX8879 in 2x mode, the IC changes to 1.5x mode
once V IN is greater than 2/3 of the output voltage.
Soft-Start
The MAX8879 includes soft-start circuitry to limit inrush
current at turn-on and mode transitions. When starting
up, the output capacitor is charged directly from the
input with a ramped current source (with no charge-
pump action) until the output voltage is near the input
voltage. After 512μs, if all the LED cathodes are not
above 100mV, the MAX8879 switches to 1.5x mode
with the LED output current ramped from 1/32 to the
programmed current in 1/32 steps. After another 512μs,
if all the LED cathodes are not above 100mV, the
MAX8879 switches to 2x mode, once again ramping
the LED current from 1/32 to the programmed current in
1/32 steps. Any time the output voltage is less than
1.25V, the soft-start routine is reset to the 1x state. Thus,
the startup time is 512μs, 1024μs, or 1536μs, depending
on what mode is required after the completion of startup.
Output-Current Settings
The output currents for the main, sub, and flash current
regulators are set using the I 2 C serial interface (see the
I 2 C Interface section). The current for the four main
LEDs is always equal and set with a single command.
Table 1. Control Data Byte
SDA CONTROL BYTE
FUNCTION
COMMAND
DATA
C2
C1
C0
D4
D3
D2
D1
D0
On/Off Control
0
0
0
Main
Sub3
Sub2
Sub1
Movie
Main Brightness
Sub1 Brightness
Sub2 Brightness
Sub3 Brightness
Movie Brightness
Flash Brightness
0
0
0
1
1
1
0
1
1
0
0
1
1
0
1
0
1
0
32-steps, 30mA/LED max
32-steps, 30mA max
32-steps, 30mA max
32-steps, 30mA max
16-steps, 51.0mA/LED max, I 2 C enable
32-steps, 100mA/LED max, active-low enable on FSH
Flash-on time
Other Functions
1
1
1
No timer (00), 0.5s (01), 1.0s
Temp derate
RGB ramp rate
(10), 2.0s (11)
Notes: C2 is MSB and D0 is LSB. Default in bold italics .
_______________________________________________________________________________________
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