MAX13256 Datasheet, PDF(15/17 Page) Maxim Integrated Products – 36V H-Bridge Transformer Driver for Isolated Supplies Integrated System Protection

◁

MAX13256

36V H-Bridge Transformer

Driver for Isolated Supplies

Transformers for use with the device are typically wound

on a high-permeability magnetic core. To minimize radi-

ated electromagnetic emissions, select a toroid, pot core,

E/I/U core, or equivalent.

Low-Voltage Operation

The MAX13256 can be operated from an +8V supply by

decreasing the turns ratio of the transformer, or by design-

ing a voltage doubler circuit as shown in Figure 3B.

Optimum performance at +8V is obtained with fewer

turns on the primary winding since the ET product

requirement is lower than for a +24V supply. However,

any of the transformers for use with a +24V supply can

operate properly with a +8V supply. For a given power

level, the transformer currents are higher with a +8V

supply than with a +24V supply. Therefore, the DC resis-

tance of the transformer windings has a larger impact on

the circuit efficiency.

Diode Selection

The high switching speed of the MAX13256 necessitates

high-speed rectifiers. Ordinary silicon signal diodes

such as 1N914 or 1N4148 can be used for low-output

current levels (less than 50mA.) But at higher output cur-

rent levels, their reverse recovery times might degrade

efficiency. At higher output currents, select low forward-

voltage Schottky diodes to improve efficiency. Ensure

that the average forward current rating for the rectifier

diodes exceeds the maximum load current of the circuit.

For surface-mount applications, Schottky diodes such as

the BAT54, MBRS140, and MBRS340 are recommended.

Capacitor Selection

Input Bypass Capacitor

Bypass the supply pin to GND with a 1FF ceramic

capacitor as close as possible to the device. The equiva-

lent series resistance (ESR) of the input capacitors is not

as critical as for the output filter capacitors. Typically

ceramic X7R capacitors are adequate.

Output Filter Capacitor

In most applications, the actual capacitance rating of the

output filter capacitors is less critical than the capacitorâs

ESR. In applications sensitive to output-voltage ripple,

the output filter capacitor must have low ESR. For optimal

performance, the capacitance should meet or exceed

the specified value over the entire operating temperature

range. Capacitor ESR typically rises at low temperatures;

however, OS-CON capacitors can be used at tempera-

tures below 0NC to help reduce output-voltage ripple in

sensitive applications. In applications where low output-

voltage ripple is not critical, standard ceramic 0.1FF

capacitors are sufficient.

Table 1. Component Manufacturers

MANUFACTURER

Central Semiconductor

Halo Electronics

Kemet

Sanyo

Taiyo Yuden

TDK

Suggested External Component Manufacturers

COMPONENT

Diodes

Transformers

Capacitors

WEBSITE

www.centralsemi.com

www.haloelectronics.com

www.kemet.com

www.sanyo.com

www.t-yuden.com

www.component.tdk.com

▷