NCP5623C View Datasheet(PDF) - ON Semiconductor

Part Name

Description

MFG CO.

NCP5623C

Triple Output I2C Controlled RGB LED Driver

ON Semiconductor 

NCP5623C

DC/DC OPERATION

The converter is based on a charge pump technique to

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.

The average forward current of each LED can be

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 by the

independent PWM controllers. 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.

The built−in OVP circuit continuously monitors the Vout

voltage and stops the converter when the voltage is above

5.7 V. The converter resumes to normal operation when the

voltage drops below 4.4 V (no latch−up mechanism).

Consequently, the chip can operate under no load conditions

during any test procedures.

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 IREF pin and Ground.

Note : due to the internal structure of this pin, no voltage,

either downward or upward, shall be forced at the IREF pin.

The reference current is multiplied by the constant

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 (Rbias

= Vref/IREF) and a more practical equation can be arranged

to define the resistor value for a given maximum output

current:

Rbias = (Vref*k)/Iout

[1]

Rbias = (0.6*2400)/Iout

Rbias = 1440/Iout

[2]

Since the Iref to ILED ratio is very high, it is strongly

recommended to set up the reference current at 12.5 mA to

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.

On the other hand, care must be observed to avoid leakage

current flowing into either the IREF pin of the bias resistor

network.

Finally, for any desired ILED current, the curve provided

Figure 4 can be recalculated according to the equation:

ILED

+

IREF @ k

31 * n

(eq. 1)

ILED

+

Vref

R

@

2400

31 * n

(eq. 2)

with: n = step value @ 1 ≤ n ≤ 31

with: R = reference resistance

with: k = internal multiplier constant = 2400

Note: n = 0 forces ILED to zero

with: n = 30 and n = 31 yields the same LED current

LOAD CONNECTION

The primary function of the NCP5623C is to control three

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.

Moreover, a built−in gradual dimming provides a smooth

brightness transition for any current level, in both Upward

and Downward direction. The dimming function is

controlled by the I2C interface: see Table 2.

The NCP5623C chip is capable to drive the three LED

simultaneously, as depicted in Figure 1, but the load can be

arranged to accommodate several LED if necessary in the

application. 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.

I2C PROTOCOL

The NCP5623C is programmed by means of the standard

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

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