LM3409EVAL National Semiconductor, LM3409EVAL Datasheet - Page 9

• Manufacturer Part Number: LM3409EVAL
• Description: BOARD EVALUATION FOR LM3409
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3409EVAL

• Current - Output / Channel: 1A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 15V
• Features: Dimmable
• Voltage - Input: 6 ~ 42 V
• Utilized Ic / Part: LM3409
• Kit Contents: Board, Datasheet
• Svhc: No SVHC (15-Dec-2010)
• Kit Features: Drives 4 LEDs At Maximum Average LED Current 1A From DC Input Voltage 24V
• Mcu Supported Families: LM3409
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

CONTROLLED OFF-TIME (COFT) ARCHITECTURE
The COFT architecture is used by the LM3409/09HV to con-
trol I
one-shot off-timer that varies with output voltage. D is indi-
rectly controlled by changes in both t
depending on the operating point. This creates a variable
switching frequency over the entire operating range. This type
of hysteretic control eliminates the need for control loop com-
pensation necessary in many switching regulators, simplify-
ing the design process and providing fast transient response.
LED
. It is a combination of peak current detection and a
FIGURE 1. Ideal CCM Buck Converter Inductor Current i
OFF
and t
FIGURE 2. Peak Current Control Circuit
ON
, which vary
9
Adjustable Peak Current Control
At the beginning of a switching period, PFET Q1 is turned on
and inductor current increases. Once peak current is detect-
ed, Q1 is turned off, the diode D1 forward biases, and inductor
current decreases.
tion is accomplished using the differential voltage signal cre-
ated as current flows through the current setting resistor
(R
adjustable current sense threshold (V
off when V
the minimum possible t
SNS
). The voltage across R
SNS
exceeds V
Figure 2
ON
L
CST
(t)
(typically 115ns).
, providing that t
shows how peak current detec-
SNS
(V
30085604
SNS
CST
) is compared to the
30085605
) and Q1 is turned
ON
is greater than
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