 English |
|
|
|
|
|
|
|
| LM3429_14 Datasheet, PDF (23/50 Pages) Texas Instruments – LM3429Q1 N-Channel Controller for Constant Current LED Drivers | |||
| |||
| ◁ |
LM3429
www.ti.com
SNVS616F â APRIL 2009 â REVISED JANUARY 2010
Single LED dynamic resistance: rLED
Nominal input voltage: VIN
Input voltage range: VIN-MAX, VIN-MIN
Switching frequency: fSW
Current sense voltage: VSNS
Average LED current: ILED
Inductor current ripple: ÎiL-PP
LED current ripple: ÎiLED-PP
Peak current limit: ILIM
Input voltage ripple: ÎvIN-PP
Output OVLO characteristics: VTURN-OFF, VHYSO
Input UVLO characteristics: VTURN-ON, VHYS
1. OPERATING POINT
Given the number of series LEDs (N), the forward voltage (VLED) and dynamic resistance (rLED) for a single LED,
solve for the nominal output voltage (VO) and the nominal LED string dynamic resistance (rD):
VO = N x VLED
(27)
rD = N x rLED
(28)
Solve for the ideal nominal duty cycle (D):
Buck
D
=
VO
VIN
(29)
Boost
D=
VO - VIN
VO
(30)
Buck-boost
D
=
VO
VO + VIN
(31)
Using the same equations, find the minimum duty cycle (DMIN) using maximum input voltage (VIN-MAX) and the
maximum duty cycle (DMAX) using the minimum input voltage (VIN-MIN). Also, remember that D' = 1 - D.
2. SWITCHING FREQUENCY
Set the switching frequency (fSW) by assuming a CT value of 1 nF and solving for RT:
Buck (Constant Ripple vs. VIN)
25 x (VIN - VO )
RT = fSW x CT X VIN
(32)
Copyright © 2009â2010, Texas Instruments Incorporated
Product Folder Links: LM3429
Submit Documentation Feedback
23
|
▷ |
German
Russian
Spanish
Italian
Polish
Chinese
Japanese
Korean
French
Portuguese