LM2793 datasheet(9/12 Pages) TI1

부품명	LM2793

상세설명	Low Noise White LED Constant Current Supply with Dual Function Brightness Control

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LM2793

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SNVS228 – MAY 2004

Figure 3. Efficiency vs. VIN

2 LEDs, VLED = 3.6V, ILED = 16mA

Efficiency (E) of the LM2793 is defined here as the ratio of the power consumed by LEDs (PLED) to the power

drawn from the input source (PIN). In the equations below, IQ is the quiescent current of the LM2793, ILED is the

current flowing through one LED, and VLED is the forward voltage at that LED current. In the input power

calculation, the 1.5 multiplier reflects the 3/2 switched capacitor gain of the LM2793.

PLED = N × VLED × ILED

(1)

PIN = VIN × IIN

(2)

PIN = VIN × (1.5 × N × ILED + IQ)

(3)

E = (PLED ÷ PIN)

(4)

It is also worth noting that efficiency as defined here is in part dependent on LED voltage. Variation in LED

voltage does not affect power consumed by the circuit and typically does not relate to the brightness of the LED.

For an advanced analysis, it is recommended that power consumed by the circuit (VIN x IIN) be evaluated rather

than power efficiency. Power consumption of the LM2793 Typical Application Circuit is shown in Figure 4.

Figure 4. ILED current vs. PIN

2 LEDs, 2.5

≤ VLED ≤ 3.9V, ILED = 16mA

THERMAL PROTECTION

When the junction temperature exceeds 150°C, the LM2793 internal thermal protection circuitry disables the part.

This feature protects the device from damage due to excessive power dissipation. The device will recover and

operate normally when the junction temperature falls below 125°C. It is important to have good thermal

conduction with a proper layout to reduce thermal resistance.

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