ncp5623 ON Semiconductor, ncp5623 Datasheet - Page 7

• Manufacturer Part Number: ncp5623
• Description: Triple Output Rgb Led Driver With I2c Control
• Manufacturer: ON Semiconductor

DC/DC OPERATION
generate a DC voltage capable to supply the RGB LED load.
The system regulates the current flowing into each LED, not
the DC Vout value, by means of internal current mirrors
associated with the diodes. Consequently, Vout = Vbat *
Mode, with Mode = 1 or Mode = 2, the extra voltage Vout
- Vf being sustained by the current mirror structure.
independently programmed (by means of the associated
PWM ) to achieve the RGB function. The maximum LED
current, setup by the external bias resistor connected across
IREF pin and Ground, is associated to the digital content of
the I2C register (see Table 1). This peak current applies to
the three LED simultaneously, but, thanks to the RGB
function, the average output current of each LED is
controlled
Consequently, the luminosity of each RGB diode can be
independently adjusted to cope with a given illumination
need. Since the peak current is constant, the color of the
RGB diodes is the one defined by the specifications of each
individual LED.
voltage and stops the converter when the voltage is above
5.3 V. The converter resumes to normal operation when the
voltage drops below 5.2 V (no latch-up mechanism).
Consequently, the chip can operate under no load conditions
during any test procedures.
LOAD CURRENT CALCULATION
voltage provided by the internal Band Gap associated to the
external resistor connected across I
Note : due to the internal structure of this pin, no voltage,
either downward or upward, shall be forced at the I
k = 2400 to yield the output load current. Since the reference
voltage is based on a temperature compensated Band Gap,
a tight tolerance resistor will provide a very accurate load
current. The resistor is calculated from the Ohm's law (R
= Vref/I
to define the resistor value for a given maximum output
current:
R
R
R
recommended to set up the reference current at 12.5 mA to
bias
bias
bias
The converter is based on a charge pump technique to
The average forward current of each LED can be
The built-in OVP circuit continuously monitors the V
The load current is derived from the 600 mV reference
The reference current is multiplied by the constant
Since the Iref to ILED ratio is very high, it is strongly
= (Vref*k)/Iout
= (0.6*2400)/Iout
= 1440/Iout
REF
) and a more practical equation can be arranged
by
the
independent
REF
PWM
pin and Ground.
controllers.
REF
http://onsemi.com
[ 1 ]
[ 2 ]
pin.
bias
out
NCP5623
7
optimize the tolerance of the output current. Although it is
possible to use higher or lower value, as defined in the
analog section, a 48 kW / 1% resistor will provide the best
compromise, the dimming being performed by the
appropriate PWM registers.
current flowing into either the IREF pin of the bias resistor
network.
Figure 4 can be recalculated according to the equation:
LOAD CONNECTION
LED arranged in the RGB color structure (reference
OSRAM LATB G66x). The brightness of each LED is
independently controlled by a set of dedicated PWM
structure embedded into the silicon chip. The peak current,
identical for each LED, is programmable by means of the
I2C data byte. With 32 steps per PWM, the chip provides
32768 colors hue in a standard display.
brightness transition for any current level, in both Upward
and Downward direction. The dimming function is
controlled by the I2C interface: see Table 2.
simultaneously, as depicted in Figure 1, but the load can be
arranged to accommodate several LED if necessary in the
application (see Figure 7). Finally, the three current mirrors
can be connected in parallel to drive a single power full LED,
thus yielding 90 mA current capability in a single LED, as
depicted in Figure 8.
I2C PROTOCOL
I2C protocol controlled by an external MCU. The
communication takes place with two serial bytes sharing the
same I2C frame:
- Byte#1 ³ physical I2C address
- Byte#2 ³ Selected internal registers & function
On the other hand, care must be observed to avoid leakage
Finally, for any desired ILED current, the curve provided
with: n = step value @ 0 ≤ n ≤ 30
with:
with:
The primary function of the NCP5623 is to control three
Moreover, a built-in gradual dimming provides a smooth
The NCP5623 chip is capable to drive the three LED
The NCP5623 is programmed by means of the standard
R = reference resistance
k = internal multiplier constant = 2400
ILED +
ILED + Iref @ k
Vref
R
32 * n
32 * n
@ 2400
(eq. 1)
(eq. 2)