ML1565 datasheet(18/21 Pages) MINILOGIC

18 / 21 page

P18/21

Rev. C, Sep 2005

ML1565

Applications Information (1)

LED, LCD, and Other Boost Applications

Any auxiliary channel can be used for a wide variety of

step-up applications. These include generation 5V or

some other voltage for motor or actuator drive, generating

15V or similar voltage for LCD bias, or generating a

step-up current source to efficiently drive a series array of

white LEDs for display backlighting. Figures 5 and 6 show

examples of these applications.

Figure 5. Using an AUX_ Controller Channel to

Generate LCD Bias

Figure 6. AUX_ Channel Powering a White LED

Step-Up Current Source

SEPIC Buch-Boost

The ML1565 ’s internal switch step-up and step-down can

be cascaded to make a high-efficiency buck-boost

converter, but it may sometimes be desirable to build a

second buck-boost converter with an AUX_ controller. One

type of step-up/step-down converter is the SEPIC (Figure

7). Inductors L1 and L2 can be separate inductors or

wound on a single core and coupled like a transformer.

Typically, a coupled inductor improves efficiency since

some power is transferred through the coupling, causing

less power to pass through the coupling capacitor (C2).

Likewise, C2 should have low ESR to improve efficiency.

The ripple current rating must be greater than the larger of

the input and output currents. The MOSFET (Q1)

drain-to-source voltage rating, and the rectifier (D1)

reverse-voltage rating must exceed the sum of the input

and output voltages. Other types of step-up/step-down

circuits are a flyback converter and a step-up converter

followed by a linear regulator.

Figure 7. Auxiliary SEPIC Configuration

ML1565

PART OF

ML 1565

ML1565 Datasheet(PDF) 18 Page - Minilogic Device Corporation Limited