LM3444MM/NOPB National Semiconductor, LM3444MM/NOPB Datasheet - Page 8

• Manufacturer Part Number: LM3444MM/NOPB
• Description: IC LED DRIVER AC-DC 10MSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3444MM/NOPB

• Constant Current: Yes
• Constant Voltage: Yes
• Internal Driver: No
• Type - Primary: General Purpose
• Type - Secondary: High Brightness LED (HBLED)
• Mounting Type: Surface Mount
• Topology: AC DC Offline Switcher, PWM, Step-Down (Buck)
• Number Of Outputs: 1
• Frequency: Adjustable/Selectable
• Voltage - Supply: 8 V ~ 13 V
• Package / Case: 10-TFSOP, 10-MSOP (0.118", 3.00mm Width)
• No. Of Outputs: 1
• Output Current: 100mA
• Operating Temperature Range: -40°C To +125°C
• Driver Case Style: MSOP
• No. Of Pins: 10
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Operating Temperature: -
• Other names: LM3444MM/NOPB; LM3444MM/NOPBTR

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VALLEY-FILL CIRCUIT
V
D3 allows V
V
the voltage ripple when the valley fill capacitors are being
The valley-fill circuit allows the buck regulator to draw power
throughout a larger portion of the AC line. This allows the ca-
pacitance needed at V
valley-fill circuit, and adds passive power factor correction
(PFC) to the application.
VALLEY-FILL OPERATION
When the “input line is high”, power is derived directly through
D3. The term “input line is high” can be explained as follows.
The valley-fill circuit charges capacitors C7 and C9 in series
(Figure
The peak voltage of a two stage valley-fill capacitor is:
As the AC line decreases from its peak value every cycle,
there will be a point where the voltage magnitude of the AC
line is equal to the voltage that each capacitor is charged. At
this point diode D3 becomes reversed biased, and the ca-
FIGURE 4. Two stage Valley-Fill Circuit when AC Line is
BUCK
BUCK
has a relatively small hold capacitor C10 which reduces
supplies the power which drives the LED string. Diode
4) when the input line is high.
BUCK
to remain high while V+ cycles on and off.
BUCK
High
to be lower than if there were no
FIGURE 3. Two and Three Stage Valley Fill Circuit
30127519
8
charged. However, the network of diodes and capacitors
shown between D3 and C10 make up a "valley-fill" circuit. The
valley-fill circuit can be configured with two or three stages.
The most common configuration is two stages.
trates a two and three stage valley-fill circuit.
pacitors are placed in parallel to each other
V
A three stage valley-fill circuit performs exactly the same as
two-stage valley-fill circuit except now three capacitors are
now charged in series, and when the line voltage decreases
to:
Diode D3 is reversed biased and three capacitors are in par-
allel to each other.
The valley-fill circuit can be optimized for power factor, volt-
age hold up and overall application size and cost. The
LM3444 will operate with a single stage or a three stage val-
ley-fill circuit as well. Resistor R8 functions as a current
limiting resistor during start-up, and during the transition from
series to parallel connection. Resistors R6 and R7 are 1 MΩ
bleeder resistors, and may or may not be necessary for each
application.
FIGURE 5. Two stage Valley-Fill Circuit when AC Line is
BUCK
equals the capacitor voltage.
Low
(Figure
30127521
Figure 3
5), and
30127518
illus-