NCP5623 데이터 시트보기 (PDF) - ON Semiconductor

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NCP5623

Triple Output I2C Controlled RGB LED Driver

ON Semiconductor 

NCP5623

LED MAXIMUM 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 ILEDmax:

Rbias = (VREF*k)/ILEDmax

[1]

Rbias = (0.6*2400)/ILEDmax

Rbias = 1440/ILEDmax

[2]

Since the IREF to ILEDmax 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 5 can be recalculated according to the equation:

ILED

+

IREF @ k

31 * n

ILED

+

VREF

Rbias

@

2400

31 * n

(eq. 1)

(eq. 2)

with: n = step value @ 1 ≤ n ≤ 31

with: Rbias = reference resistance

with: k = internal multiplier constant = 2400

Note: n=0 − ILED is set to zero

n = 31 − ILED is set to the same current as n = 30

LOAD CONNECTION

The primary function of the NCP5623 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 maximum

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 NCP5623 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 powerful LED, thus

yielding 90 mA current capability in a single LED.

I2C PROTOCOL

The NCP5623 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

B7

B6

B5

B4

B3

B2

B1

B0

Byte#1 : I2C Physical Address, based 7 bits : % 011 1000 ³ $38 *

0

1

1

1

0

0

0

R/W

Byte#2 : DATA register

RLED2

RLED1

RLED0

BLED4

BLED3

BLED2

BLED1

BLED0

*Note: according to the I2C specifications, the physical address is based on 7 bits out of the SDA byte, the 8th bit representing the R/W command.

Since the NCP5623 is a receiver only, the R/W command is 0 and the hexadecimal byte send by the MCU is %0111 0000 = $70

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