NCP5608
http://onsemi.com
10
OUTPUT LED PROGRAMMING SEQUENCE
Once the maximum output current has been set up by the
external resistor (see Load Current Calculation paragraph
above), the I2C protocol can be used to dynamically adjust
the brightness of the selected block.
At this point, the dimming of each block depends upon
the content of the appropriate register (PWRLD_BK[4..0]
or PWRLED_FL[6..0]). The LED current can be
calculated according to the digital value stored into the
registers.
The LED can be programmed in four steps:
1. Define the maximum ILEDBK−MAX and
ILEDFL−MAX currents requested by the Back
Light and Flash applications (set by external
resistors). This is the maximum current that will
be reached when the registers will be at their
respective full range (PWRLD_BK[4..0] = $1F =
31 Decimal, PWRLED_FL[6..0] = $7F= 127
decimal).
2. Calculate the reference current (Irefbk and Ireffl ):
Irefbk = ILED−BK/1200 and
Ireffl = ILED−FL/4000
3. Calculate the external resistor value
RBK = 0.6/Irefbk
RFL = 0.6/Ireffl
4. The dimming of flash and backlight LED will be
now achieved by changing the PWRLD_BK[4..0]
and PWRLED_FL[6..0] registers content to get the
operating LED current along the curves 0 mA to
ILED−BK−MAX mA and 0 mA to ILED−FL mA:
BK−NSteps = number of steps stored into the
PWRLD_BK register (value, in decimal, of the
PWRLD_BK[4..0] register)
FL−NSteps = number of steps stored into the
PWRLED_FL register (value, in decimal, of the
PWRLD_FL[6..0] register)
ILEDBK = (ILEDBK−MAX/31) * BK−NSteps
ILEDFL = (ILEDFL−MAX/127) * FL−NSteps
PHYSICAL ADDRESS
The physical I2C address dedicated to the NCP5608 to support the I2C protocol is: 0111 001X → $72. The external
controller must fulfill the I2C protocol to drive the chip: see I2C−BUS SPECIFICATION, Version 2.1. The NCP5608
operates as a Slave only and never takes over the I2C control.
Table 3. NCP5608 Operation Truth Table
PWRLED_BK (0−7) PWRLED_FL (0−7) Output Voltage Comments
$00 $00 Forced to zero DC−DC = OFF
>$80 X Vfbk + Vsense DC−DC = ON, LED1 to LED4 active
>$00 X Vfbk + Vsense DC−DC = ON, LED1 to LED3 active
LED4 deactivated
X >$00 Vffl + Vsense DC−DC = ON
The I2C protocol is based on the standard format defined
in the industry. Basically, the DATA is transferred from the
MCU to the NCP5608 registers by means of the SDA
message associated to the SCL clock. The MCU presents
the 8 bits during the low state of the SCK signal and the
peripheral device ( in our case, the NCP5608) shall reads
the bits during the high state of the same clock. The transfer
is MSB first as depicted in Figure 5.
DATA
CLOCK
MPU send bit
The NCP5608 reads one bit
MPU enables clock
The NCP5608 send ACK
B0B1B2B3B4B5B6B7
Start
ACK B0B1B2B3B4B5B6B7 ACK
Stop
PHYSICAL ADDRESS FRAME DATA FRAME
NOTE: See I2C−BUS SPECIFICATION, Version 2.1, January 2000, for further timing details.
Figure 5. Basic I2C Timings
