NCP5623BMUTBG Datasheet NCP5623BMUTBG | P7-P9

NCP5623B

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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 current setting resistor

connected across IREF pin and Ground, is associated to the

digital content of the I

C 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 V

out

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 I

REF

pin and Ground.

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

either downward or upward, shall be forced at the I

REF

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 (R

set

= Vref/I

REF

) and a more practical equation can be arranged

to define the resistor value for a given maximum output

current:

set

= (Vref*k)/Iout [ 1 ]

set

= (0.6*2400)/Iout

set

= 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 or the current setting

resistor.

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

Rset

@ 2400

31 * n

(eq. 2)

with: n = step value @ 1 ≤ n ≤ 30

with: Rset = Current setting resistor

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 NCP5623B 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

C 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 I

C interface: see Table 2.

The NCP5623B 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.

C PROTOCOL

The NCP5623B is programmed by means of the standard

C protocol controlled by an external MCU. The

communication takes place with two serial bytes sharing the

same I

C frame:

− Byte#1 ³ physical I

C address

− Byte#2 ³ Selected internal registers & function

NCP5623B

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B6 B5 B4 B3 B2 B1 B0

Byte#1 : I

C Physical Address, based 7 bits : % 011 1000 ³ $38 *

1 1 1 0 0 0 R/W

Byte#2 : DATA register

B6 B5 B4 B3 B2 B1 B0

*Note: according to the I

C specifications, the physical address is based on 7 bits out of the SDA byte, the 8

bit representing the R/W command.

Since the NCP5623B is a receiver only, the R/W command is 0 and the hexadecimal byte send by the MCU is %0111 0000 = $70

B[7:5]: INTERNAL REGISTER SELECTION:

B7 B6 B5 Function

0 0 0 Chip Shut Down ³ all LED current = zero

0 0 1 Set up the maximum Output LED Current step

0 1 0 PWM1 : LED1 control

0 1 1 PWM2 : LED2 control

1 0 0 PWM3 : LED3 control

1 0 1 Set the Upward IEND target

1 1 0 Set the Downward IEND target

1 1 1 Set step time and activate the Gradual Dimming

The contain of bits B[4:0] depends upon the type of function selected by bits B[7:5] as depicted in Table 1

Table 1. INTERNAL REGISTER BITS ASSIGNMENT

B7 B6 B5 B4 B3 B2 B1 B0 Comments

0 0 0 X X X X X Shut down

0 0 1 16 8 4 2 1 Maximum Output LED Current Step see

Figure 4 (Note 11)

0 1 0 BPWM16 BPWM8 BPWM4 BPWM2 BPWM1 PWM1

0 1 1 BPWM16 BPWM8 BPWM4 BPWM2 BPWM1 PWM2

1 0 0 BPWM16 BPWM8 BPWM4 BPWM2 BPWM1 PWM3

1 0 1 GDIM5

GDIM4

GDIM3

GDIM2

GDIM1

Set Gradual Dimming

Upward IEND Target (Note 12)

1 1 0 GDIM5

GDIM4

GDIM3

GDIM2

GDIM1

Set Gradual Dimming

Downward IEND Target (Note 12)

1 1 1 GDIM5

128 ms

GDIM4

64 ms

GDIM3

32 ms

GDIM2

16 ms

GDIM1

8 ms

Gradual Dimming

Step Time & run

11. The programmed current applies to the three LED simultaneously, the gradual dimming is not engaged

12.The bit values represent the steps count, not the ILED current: see equations 1 & 2, page 7, to derive the ILED value.

GRADUAL DIMMING

The purpose of that function is to gradually Increase or

Decrease the brightness of the backlight LED upon

command from the external MCU. The function is activated

and controlled by means of the I

C protocol.

In order to avoid arithmetic division functions at silicon

level, the period (either upward or downward) is equal to the

time defined for each step, multiplied by the number of

steps.

To operate such a function, the MCU will provide three

information:

1 – The target current level (either upward or downward)

2 – The time per step

3 – The Upward or Downward mode of operation

When a new gradual dimming sequence is requested, the

output current increases, according to an exponential curve,

from the existing start value to the end value. The end current

value is defined by the contain of the Upward or Downward

registers, the width of each step is defined by the last register

(B7 = B6 = B5 = 1), the number of step being in the 1 to 30

range. In the event of software error, the system checks that

neither the maximum output current (30 mA), nor the zero

level are forced out of their respective bounds. Similarly:

software errors shall not force the NCP5623B into an

uncontrolled mode of operation. not recommended to

NCP5623B

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trigger another gradual dimming when current gradual

dimming is running. If IEND is set to be lower than start

current level for upward gradual dimming, after gradual

dimming is triggered, LED current will rise from current

level to maximum, drop to zero and start from zero to IEND

then. It’s similar if IEND is higher than start current level for

downward gradual dimming.

The dimming is built with 30 steps and the time delay is

encoded into the second byte of the I

C transaction: see

Table 1.

When the gradual dimming is deactivated (B7 = B6 = 0,

B5 = 1), the output current is straightforwardly set up to the

level defined by the contain of the related register upon

acknowledge of the output current byte.

The gradual dimming sequence must be completed before

a new output current data byte is send to the NCP5623B . At

this point, the brightness sequence takes place when the new

data byte is acknowledged by the internal I

C decoder. Since

the six registers are loaded on independent byte flow

associated to the I

C address, any parameter of the

NCP5623B chip can be updated ahead of the next function

as depicted in Table 2.

Table 2. BASIC PROGRAMMING SEQUENCES

C Address COMMAND Bits[7:0] Operation Note

$70 000X XXXX System Shut Down Bits[4:0] are irrelevant

$70 0010 0000

0011 1111

Set Up the ILED current ILED register

Bits[4:0] contain the IMAX value as defined by the

Iref value

$70 0100 0000

0101 1111

Set Up the PWM1 PWM1

Bits[4:0] contain the PWM value

$70 0110 0000

0111 1111

Set Up the PWM2 PWM2

Bits[4:0] contain the PWM value

$70 1000 0000

1001 1111

Set Up the PWM3 PWM3

Bits[4:0] contain the PWM value

$70 1010 0000

1011 1111

Set Up the IEND Upward UPWARD

Bits[4:0] contain the IEND value

$70 1100 0000

1101 1111

Set Up the IEND Downward DWNWRD

Bits[4:0] contain the IEND value

$70 1110 0000

1111 1111

Set Up the Gradual Dimming time

and run the sequence

GRAD

Bits[4:0] contain the TIME value

The number of step for a given sequence, depends upon

the start and end output current range: since the IPEAK

value is encoded in the Bits[4:0] binary scale, a maximum

of 31 steps is achievable during a gradual dimming

operation.

The number of steps will be automatically recalculated by

the chip according to the equation:

Nstep = | existing step position − new step position |

As an example, assuming the previously programmed

step was 5 and the new one is 15, then we will have 10 steps

to run between the actual location to the end value. If the

timing was set at 16 ms, the total gradual dimming sequence

will be 160 ms.

To select the direction of the gradual dimming (either

Upward or Downward), one shall send the appropriate

1010 1111 ³ 1110 0011 ³ select an UPWARD sequence

with 24 ms/step, the end IPEAK current being (IREF *

2400) / (31 − 16) mA.

1100 0001 ³ 1110 0100 ³ select the DOWNWARD

sequence with 32 ms/step, the end IPEAK current being

(IREF * 2400) / (31 − 1) mA.

P1-P3 P4-P6 P7-P9 P10-P12

NCP5623BMUTBG

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LED Lighting Drivers RGB LED DRIVER W/I2C

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