AP1651BEL Datasheet, PDF (14/28 Pages) Asahi Kasei Microsystems – Dimmable LED driver IC for Lighting

[AP1651BEL]
■ Dimming Control
1) Complex Dimming by the ADIM pin
Wide dimming range using the ADIM pin is available. One of the following three modes of dimming
operation: “peak current control mode”, “peak current control with PWM dimming mode” and “linear
regulator mode” is chosen by the ADIM pin voltage. The input voltage range of the ADIM pin is from 0V to
VREF(5V(typ)). The LED current is changed by the applied input voltage when it is less than 4V as Figure 8
shows.
Figure 8. Complex Dimming by DC input (ADIM pin)
A brief overview of the three dimming methods by using the ADIM pin voltage, as shown on Figure 8, is as
follows:
By decreasing the ADIM pin voltage below 5V, the peak current control starts from 4V. In this mode, the
average current goes down by decreasing the peak current under constant hysteresis width control.
When the bottom current drops to a certain level, “peak current control with PWM dimming” mode is
started. In this time, the peak current stops decreasing at the ADIM’ voltage shown in Figure 8, and
simultaneously, PWM dimming starts. The value of the ADIM’ is approximately determined by the RVLY
pin voltage defined by the ripple amplitude as following formula:
ADIM '  2  0.3375 V_REF  V_RVLY  _…(14)
• The average current is adjustable from 100% to 1% by changing the ADIM pin voltage in the range of
V_ADIM3 (V_REF to 1.5V).
• There is an invariable zone between 1.5V to 1V of the ADIM pin voltage where the average current cannot
be changed at all.
• When the ADIM pin voltage is less than 1V, “linear regulator mode” starts. In this mode the switching
operation stops (external N-channel power MOSFET is always off), and an internal constant current source
connected to the DRAIN pin is active instead. The LED current can be dimmed from approximately 500µA
to 100µA by tuning the ADIM pin voltage between 1V(typ) and 0.2V(typ).
• If the ADIM pin voltage is less than 0.05V, the operation mode is changed from the constant current source
mode to LED current off mode in which the LED turns OFF.
• Operation of the PWM dimming in Peak + PWM state is the same as PWM dimming by the PDIM pin
mentioned in the next paragraph except using an internal triangle waves.
014003479-E-01
- 14 -
2014/10