MAX5025 查看數據表（PDF） - Maxim Integrated

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产品描述 (功能)

比赛名单

MAX5025

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

Maxim Integrated 

500kHz, 36V Output, SOT23,

Step-Up DC-DC Converters

ULVO

OSCILLATOR

THERMAL

SHUTDOWN

3 FB

REF

2 GND

5 VCC

MAIN PWM

COMPARATOR

-A

+A

CONTROL

LOGIC

+C

-C

CURRENT-

LIMIT

COMPARATOR

SHDN 4

LX 6

N

PGND 1

MAX5025

MAX5026

Figure 1. Functional Diagram

R1

=

R2

⎛

⎝⎜

VOUT

VREF

⎞

-1⎠⎟

where VREF is 1.25V

Determining Peak Inductor Current

If the boost converter remains in the discontinuous

mode of operation, then the approximate peak inductor

current, ILPEAK, is represented by the formula below:

( ) ILPEAK =

2 TS VOUT − VIN IOUT

ηL

where TS is the period, VOUT is the output voltage, VIN

is the input voltage, IOUT is the output current, and η is

the efficiency of the boost converter.

Determining the Inductor Value

47µH is the recommended inductor value when the out-

put voltage is 30V and the input voltage is 5V. In gener-

al, the inductor should have a current rating greater

than the current-limit value. For example, the inductor’s

current rating should be greater than 150mA to support

a 4mA output current. Equivalent series resistance

(ESR) should be below 1Ω for reasonable efficiency.

Due to the MAX5025–MAX5028’s high switching fre-

quency, inductors with a ferrite core or equivalent are

recommended. Powdered iron cores are not recom-

mended due to their high losses at frequencies over

500kHz. Table 1 shows a list of vendors and 47µH

inductor parts.

For 4mA output current and output voltages other than

30V, the inductor can be simply scaled in value

according to the following formula:

L

=

(47μH) (VOUT − ) VIN

(25V)

Use the following formula to calculate the upper bound

of the inductor value at different output voltages and

output currents. This is the maximum inductance value

for discontinuous mode operation.

( ) LUPPER

=

V2

IN

VOUT − VIN TSη

2 IOUT VO2UT

Calculate the lower bound, LLOWER, for the acceptable

inductance value using the following formula, which will

allow the maximum output current to be delivered with-

out reaching the peak current limit:

( ( )) LLOWER

=

2 TS VOUT − VIN IOUT

η

⎛

⎝⎜

VIN

5

260mA

⎞

⎠⎟

2

Notice that the switch current limit, (VIN/5)(260mA), is a

function of the input voltage, VIN. The current rating of

the inductor should be greater than the switch current

limit.

Table 1. Inductor Vendors

VENDOR

Coilcraft

Sumida

Toko

PHONE

847-639-6400

847-545-6700

847-297-0070

FAX

847-639-1469

847-545-6720

847-699-7864

PART NUMBER OF 47µH INDUCTOR

DT1608C-473

CDRH4D28-470

A915BY-470M

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