RL1632R-R100-F datasheet(10/22 Pages) ONSEMI

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NCV78514

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Digital Dimming

A first dimming functionality is achieved by applying

a square input signal on the DIM pin.

The input duty cycle range is valid in the DIM_DC_IN

range and is reconstructed on the output with an identical

duty cycle (DIM_DC_OUT).

A duty cycle above 98% is considered as a 100 % duty

cycle. The current into the LEDs is then no more dimmed,

and set to the DC current, programmed by RSET.

As soon as the part achieves 100 % duty cycle, the part

enters in automatic mode.

At start up, the NCV78514 starts after the second

identified valid duty cycle.

A duty cycle change, to a higher or lower value, makes

a linear change of the LED current. The time to reach new

current is proportional to difference of new and previous

duty cycle and is described below.

Figure 4. ILED Setting Slope in Digital Dimming Mode

A = Old Duty

Cycle: 20 %

0.2

0.5

t (ms)

P_DIM_DETECT

B = New Duty

Cycle: 50 %

Duty cycle:

0 %

P_DIM_DETECT

 P_FADING_TIME

B - A

100

P_DIM_DETECT +

Automatic Fading

Automatic fading mode is activated if the voltage applied

to PWM pin is not alternating during the P_DIM_DETECT

period. When the PWM pin is held active for this period, the

output current will reach programmed value after

P_FADING_TIME and the current rise will be logarithmic.

When logic 0 is applied for another period of

P_DIM_DETECT, the output current will start to decline to

in logarithmic manner. Zero output current will be reached

after P_FADING_TIME.

Remark: depending on the output conditions (I.E low

current level, high LED number), the small duty cycle

values can create long turn on time of the LED string.

Figure 5. ILED Setting Slope, Automatic Fading Mode

t (ms)

P_DIM_DETECT

P_FADING_TIME

P_DIM_DETECT

P_FADING_TIME

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