500kHz, 36V Output, SOT23, PWM Step-Up

DC-DC Converters

10

______________________________________________________________________________________

4mA,

and

and

The choice of 47µH as the recommended inductance

value is reasonable given the worst-case scenario

above. In general, the higher the inductance, the lower

the switching noise. Load regulation is also better with

higher inductance.

Diode Selection

The MAX5025–MAX5028’s high switching frequency

demands a high-speed rectifier. Schottky diodes are

recommended for most applications because of their

fast recovery time and low forward-voltage drop.

Ensure that the diode’s peak current rating is greater

than or equal to the peak inductor current. Also, the

diode reverse breakdown voltage must be greater than

Capacitor Selection

Output Filter Capacitor

The output filter capacitor should be 1µF or greater. To

achieve low output ripple, a capacitor with low ESR, low

ESL, and high capacitance value should be selected.

For very low output ripple applications, the output of the

boost converter can be followed by an RC filter to fur-

ther reduce the ripple. Figure 3 shows a 100

Ω, 1µF fil-

ter used to reduce the switching output ripple to

1mVp-p.

X7R ceramic capacitors are better for this boost appli-

cation because of their low ESR and tighter tolerance

over temperature than the Y5V ceramic capacitors.

Table 3 below lists manufacturers of recommended

capacitors.

Input Capacitor

the IC as is practical.

Applications Information

Layout Considerations

The MAX5025–MAX5028 switch at high speed, man-

dating careful attention to layout for optimum perfor-

mance. Protect sensitive analog grounds by using a

star ground configuration. Minimize ground noise by

connecting GND, PGND, the input bypass-capacitor

ground lead, and the output-filter ground lead to a sin-

gle point (star ground configuration). Also, minimize

Table 2. Schottky Diode Vendors

VENDOR

PHONE

FAX

PART NUMBERS

Comchip

510-657-8671

510-657-8921

CDBS1045

Panasonic

408-942-2912

408-946-9063

MA2Z785

ST-Microelectronics

602-485-6100

602-486-6102

TMMBAT48

Vishay-Telefunken

402-563-6866

402-563-6296

BAS382

Zetex

631-360-2222

631-360-8222

ZHCS500

Table 3. Capacitor Table

COMPANY

PHONE

FAX

PART NUMBERS

GRM42-2X7R105K050AD (1µF capacitor)

Murata

814-237-1431

814-238-0490

GRM32-1210R71C475R (4.7µF capacitor)

UMK325BJ105KH (1µF capacitor)

Taiyo Yuden

408-573-4150

408-573-4159

EMK316BJ475ML (4.7µF capacitor)

C3225X7R1H155K (1.5µF capacitor)

TDK

847-803-6100

847-803-6296

C3225X7R1H105K (1µF capacitor)