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参数资料
| 型号： | NCP5608EVB |
| 厂商： | ON Semiconductor |
| 文件页数： | 8/16页 |
| 文件大小： | 0K |
| 描述： | EVAL BOARD FOR NCP5608 |
| 设计资源： | NCP5608EVB BOM NCP5608EVB Gerber Files NCP5608EVB Schematic NCP5608 Demo Brd BOM |
| 标准包装： | 1 |
| 电流 - 输出 / 通道： | 500mA |
| 输出及类型： | 8，非隔离 |
| 输出电压： | 4.8 ~ 5.5 V |
| 特点： | 亮度控制 |
| 输入电压： | 3.6V |
| 已供物品： | 板 |
| 已用 IC / 零件： | NCP5608 |
| 其它名称： | NCP5608EVBOS |
NCP5608
LOAD CURRENT CALCULATION
The load current is derived from the 600 mV reference
voltage provided by the internal band gap associated to the
external resistor connected across the I REFBK and I REFFL
pins and GND (see Figure 4). In any case, no voltage shall
be forced at I REFBK or I REFFL pins, either downward or
upward. The backlight block, LED1 ? LED4, is powered by
Vbat
V OUT
PIN 18
the current reference defined at the I REFBK pin. The output
current can be dimmed by means of a dynamic modulation
of the I REFBK pin.
The I REFBK reference current is multiplied by the
+
?
600 mV
LEDx
PWRGND
constant ka to yield the output backlight LED load current.
Since the reference voltage is based on a temperature
compensated bandgap, a tight tolerance resistor will
provide a very accurate load current.
The ka parameter is derived from the constant 40
multiplied by the binary defined in the PWRLED_BK
register. Consequently, ka varies from 40 (1.0 mA
PIN 3
I REFBK
R1
ANALOG
CONTROL
GND
PIN 13
RBK + (0.6 * 1200) Iout
Figure 4. Typical Backlight
RFL + (0.6 * 4000) Iout
output/LED) to 1200 to support the full output current
range. The resistor is calculated from the Ohm’s law
(R = Vref/I REF ) and a more practical equation can be
arranged to define the resistor value for a given output
current:
Let Iout = 4*I LED , then:
RBK + (Vref * ka * 30) Iout
(eq. 1)
RBK + 720 Iout
Consequently, the resistor value will range between
R BK = 720/(30 mA*4) = 6000 W and
R BK = 720/(0.5 mA*4) = 360 k W for the low power block.
Similarly, the PowerFlash block, LED5?LED8, is
powered by the current reference defined at the I REFFL
pin. The same calculation as before applies, assuming
kb = 40, the maximum output current being 100 mA/LED:
Let Iout = 4*I LED , then:
RFL + (Vref * kb * 100) Iout
(eq. 2)
RFL + 2400 Iout
Finally, the resistor value will range between
R FL = 2400/(100 mA*4) = 6000 W and
R FL = 2400/(1 mA*4) = 600 k W for the High Power Flash
block.
On the other hand, the output currents can be dimmed by
means of a dynamic modulation of their respective
I REFBK /I REFFL pins current references. Obviously, the
tolerance of such resistors must be 1% or better, with a
GND
Reference Current Operation
(Similar Circuit Applies for Power Flash Section)
Note: Due to relative high impedance connected at the
reference current pins, cares must be observed to minimize
the noise pick?up and stray current present at PCB level.
Multi layer layout, with dedicated ground screen, is
mandatory.
SERIAL LINK I2C PROTOCOL
The chip is remotely controlled by means of a byte
transferred along a serial link between the MCU and the
NCP5608. The industrial standard I2C protocol is used,
although one can drive the SCL and SDA signal from
standard MCU I/O pins . Two dedicated internal registers
are used to decode the SDA content and to store the output
currents.
The I2C message carries three bytes within the same
frame:
Byte #1:
The content of this byte is the physical address
of the NCP5608 in the I2C bus.
Byte #2:
The content of this byte contains the address
of the selected block.
Byte #3:
This byte contains the output current value to
set up the selected block.
100 ppm thermal coefficient, to get the expected overall
tolerance.
http://onsemi.com
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