ZXLD1352 데이터 시트보기 (PDF) - Zetex => Diodes

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ZXLD1352

350mA LED driver with internal switch and enhanced PWM dimming range

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ZXLD1352

Inductor selection

Recommended inductor values for the ZXLD1352 are in the range 47␮H to 220␮H.

Higher values of inductance are recommended at higher supply voltages in order to minimize

errors due to switching delays, which result in increased ripple and lower efficiency. Higher

values of inductance also result in a smaller change in output current over the supply voltage

range. (See graphs). The inductor should be mounted as close to the device as possible with low

resistance connections to the LX and VIN pins.

The chosen coil should have a saturation current higher than the peak output current and a

continuous current rating above the required mean output current.

Suitable coils for use with the ZXLD1352 are listed in the table below:

Part No.

DO1608C

MSS6132ML

CD104-MC

NP04SB470M

L

(␮H)

47

47

68

100

220

47

DCR

(⍀)

0.64

0.38

0.58

0.82

0.55

0.27

ISAT Manufacturer

(A)

0.5

0.56

CoilCraft

0.47

0.39

0.53 Sumida

0.38 Taiyo Yuden

The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times

within the specified limits over the supply voltage and load current range.

The following equations can be used as a guide, with reference to Figure 1 - Operating

waveforms.

LX Switch 'On' time

TON

=

----------------------------------------L----Δ----I---------------------------------------

VIN – VLED – Iavg(RS + rL + RLX)

Note: TONmin>200ns

LX Switch 'Off' time

TOFF

=

-------------------------------L----Δ----I-------------------------------

VLED + VD + Iavg(RS + rL)

Note: TOFFmin>200ns

Where:

L is the coil inductance (H)

rL is the coil resistance (⍀)

Iavg is the required LED current (A)

⌬I is the coil peak-peak ripple current (A) {Internally set to 0.3 x Iavg}

VIN is the supply voltage (V)

VLED is the total LED forward voltage (V)

RLX is the switch resistance (⍀)

VD is the diode forward voltage at the required load current (V)

Issue 1 - August 2008

16

© Diodes Incorporated 2008

www.zetex.com

www.diodes.com

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