LM3444MASLASHNOPB.B datasheet(22/38 Pages) TI2

22 / 38 page

C11 =

tOFF

1.276

VLED

= 175 pF

VLED

R4 =

= 360 k:

ICOLL

25.2V

135 2

u 3.23 Ps = 638 ns

0.8

tON (MIN) =

25.2V

135 2

0.8

25.2V

115

(250 kHz)

= 3.23 Ps

0.8

tOFF =

VBUCK(MAX) = 135 2 = 190V

VBUCK(MIN) =

x SIN(135

= 45V

LM3444

SNVS682D – NOVEMBER 2010 – REVISED DECEMBER 2015

www.ti.com

Typical Application (continued)

8.2.1 Design Requirements

Known:

1. Input voltage range (90 VAC to 135 VAC)

2. Number of LEDs in series = 7

3. Forward voltage drop of a single LED = 3.6 V

4. LED stack voltage = (7 × 3.6 V) = 25.2 V

Choose:

1. Nominal switching frequency, fSW-TARGET = 350 kHz

2. ILED(AVE) = 400 mA

Δi (usually 15% to 30% of ILED(AVE)) = (0.30 × 400 mA) = 120 mA

4. Valley-fill stages (1, 2, or 3) = 2

5. Assumed minimum efficiency = 80%

8.2.2 Detailed Design Procedure

Calculate:

1. Calculate minimum voltage VBUCK, as shown in Equation 35, which yields:

(35)

2. Calculate maximum voltage VBUCK, as shown in Equation 36, which yields:

(36)

3. Calculate tOFF at VBUCK nominal line voltage, as given by Equation 37.

(37)

4. Calculate tON(MIN) at high line to ensure that tON(MIN) > 200 ns, as given by Equation 38.

(38)

5. Calculate C11 and R4 in steps 6 through 9.

6. Choose current through R4 (from 50 µA to 100 µA): 70 µA as given by Equation 39.

(39)

7. Use a standard value of 365 k

Ω.

8. Calculate C11 as given by Equation 40.

(40)

9. Use standard value of 120 pF.

10. Calculate ripple current: 400 mA × 0.30 = 120 mA

11. Calculate inductor value at tOFF = 3 µs as given by Equation 41.

Submit Documentation Feedback

Product Folder Links: LM3444

LM3444MA/NOPB.B Datasheet(PDF) 22 Page - Texas Instruments

LM3444MA/NOPB.B Datasheet(HTML) 22 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

Datasheet Download

Link URL