ZXLD1352 데이터 시트보기 (PDF) - Zetex => Diodes

부품명

상세내역

제조사

ZXLD1352

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

Zetex => Diodes 

ZXLD1352

Example:

For VIN =12V, L=47␮H, rL=0.64⍀, VLED=3.4V, Iavg =350mA and VD =0.36V

TON = (47e-6 x 0.105)/(12 - 3.4 - 0.672) = 0.622␮s

TOFF = (47e-6 x 0.105)/(3.4 + 0.36 + 0.322)= 1.21␮s

This gives an operating frequency of 546kHz and a duty cycle of 0.34.

These and other equations are available as a spreadsheet calculator from the Zetex website.

Go to www.zetex.com/ZXLD1352

Note that in practice, the duty cycle and operating frequency will deviate from the calculated

values due to dynamic switching delays, switch rise/fall times and losses in the external

components.

Optimum performance will be achieved by setting the duty cycle close to 0.5 at the nominal

supply voltage. This helps to equalize the undershoot and overshoot and improves temperature

stability of the output current.

Diode selection

For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance

Schottky diode with low reverse leakage at the maximum operating voltage and temperature. The

recommended diode for use with this part is the ZLLS1000. This has approximately ten times

lower leakage than standard Schottky diodes, which are unsuitable for use above 85°C. It also

provides better efficiency than silicon diodes, due to a combination of lower forward voltage and

reduced recovery time.

The table below gives the typical characteristics for the ZLLS1000:

Diode

ZLLS1000

Forward voltage

at 100mA

(mV)

310

Continuous

current

(mA)

1000

Reverse Leakage

At 30V 85°C

(␮A)

300

Package Manufacturer

TSOT23 Zetex

If alternative diodes are used, it is important to select parts with a peak current rating above the

peak coil current and a continuous current rating higher than the maximum output load current.

It is very important to consider the reverse leakage of the diode when operating above 85°C.

Excess leakage will increase the power dissipation in the device.

The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will

increase the peak voltage on the LX output. If a silicon diode is used, care should be taken to

ensure that the total voltage appearing on the LX pin including supply ripple, does not exceed the

specified maximum value.

Issue 1 - August 2008

17

© Diodes Incorporated 2008

www.zetex.com

www.diodes.com

Share Link: