LM3414SDX National Semiconductor Corporation, LM3414SDX Datasheet - Page 14

• Manufacturer Part Number: LM3414SDX
• Description: Lm3414/lm3414hv 1a 60w* Common Anode Capable Constant Current Buck Led Driver Requires No External Current Sensing Resistor
• Manufacturer: National Semiconductor Corporation

www.national.com
PULSE-LEVEL-MODULATION (PLM) OPERATION
PRINCIPLES
The Pulse-Level-Modulation is a patented method to ensure
accurate average output current regulation without the need
of direct output current sensing. Figure 3 shows the current
waveforms of a typical buck converter under steady state,
where, I
current flowing into the LX pin. For a buck converter operating
in steady state, the mid-point of the RAMP section of the main
switch current is equal to the average level of the inductor
current hence the average output current. In short, by regu-
lating the mid-point of the RAMP section of the main switch
current with respect to a precise reference level, PLM
achieves output current regulation by sensing the main switch
current solely.
L1
is the inductor current and I
FIGURE 4. LED Current Slews up with Multiple Switching Cycle
LX
is the main switch
14
PWM DIMMING CONTROL
The DIM pin of the LM3414/14HV is an input with internal pull-
up that accepts logic signals for average LED current control.
Applying a logic high (above 1.2V) signal to the DIM pin or
leaving the DIM pin open will enable the device. Applying a
logic low signal (below 0.9V) to the DIM pin will disable the
switching activity of the device but maintain VCC regulator
active. The LM3414/14HV allows the inductor current to slew
up to the preset regulated level at full speed instead of charg-
ing the inductor with multiple restrained switching duty cycles.
This enables the LM3414/14HV to achieve high speed dim-
ming and very fine dimming control as shown in Figure 4 and
Figure 5:
30124824