AL1676 datasheet(11/15 Pages) DIODES

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AL1676

Document number: DS38290 Rev. 1 - 2

11 of 15

www.diodes.com

February 2016

AL1676

Functional Description and Application Information (Cont.)

The AL1676 controls the system operating at boundary conduction mode which results in its operating frequency inconstant. To set the minimum

switching frequency fMIN at the crest of the minimum AC input.

( 2

)

RMS

PEAK

RMS

MIN







…………… (9)

According to the Faraday

’s Law of Induction, the winding number of the inductance can be calculated by:

PEAK







…………… (10)

Where,

Ae is the core effective area.

Bm is the maximum magnetic flux density.

The AL1676 has designed the minimum tON time and maximum tON time, the tON_MIN is about 700ns and the tON_MAX time is about 29µs. In buck

topology there is the equation VIN_RMS-VO=L*IPEAK/tON. If the inductance is too small, it will make tON smaller than tON_MIN, the device cannot

detect the peak current of the system, resulting in incorrect output current. If the inductance is too large, make tON longer than the tON_MAX, the

system

’s output current will decrease because of the limit of the tON_MAX.

The AL1676 has also the limitation of minimum tOFF time and maximum tOFF time, the tOFF_MIN time is about 6µs and tOFF_MAX time is about 180µs.

In buck topology there is the equation VO=L*IPEAK/tOFF. If the inductance is too small, make tOFF smaller than tOFF_MIN, the system will enter DCM

mode, and the output current will be incorrect. If the inductance is too large, make tOFF longer than tOFF_MAX, the system will enter CCM mode, and

the output current will also be incorrect. So a suitable value of the inductance is very important.

Consider these parameters, two examples of the typical application inductance is recommended as below:

System spec

Inductance Value

System Frequency

tON_MIN

tOFF

60V/100mA (85~265VAC)

2.2mH

64KHz(230 VAC)

2.4µs (265 VAC)

12.6µs

42V/150mA (85~265 VAC)

1.1mH

64KHz(230 VAC)

1.6µs (265 VAC)

13.5µs

Recommended Applications

The AL1676 integrates different MOSFET to adapt different wattage application. The output current is limited by the integrated MOSFET, and the

SO-7 package

’s heat dissipation capability. The minimum output voltage is limited by the LEB time, and the minimum output voltage is

recommended to 20V. The recommended application is given below:

Device

Output Power Coverage

Maximum Output Current

Minimum Output Voltage

AL1676-20A

≤10W

≤200mA

20V

AL1676-30A

≤13W

≤300mA

20V

AL1676-10B

≤7W

≤120mA

20V

AL1676-20B

≤10W

≤200mA

20V

AL1676-20C

≤10W

≤200mA

20V

AL1676-40D

≤18W

≤350mA

20V

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