AME5145 datasheet(12/23 Pages) AME

12 / 23 page

AME

1.6 MHz Boost Converter with

30V Internal FET Switch

AME5145

Rev.B.01

n Application Hints

Calculating Load Current

The load current is related to the average inductor cur-

rent by the relation:

LOAD = IIND (AVG) x (1 - D)

Where

“D” is the duty cycle of the application. The

switch current can be found by:

SW = IIND (AVG) + 1 /2 (IRIPPLE)

Inductor ripple current is dependent on inductance, duty

cycle, input voltage and frequency:

RIPPLE = D x (VIN-VSW) / (f x L)

Combining all terms, we can develop an expression

which allows the maximum available load current to be

calculated:

Thermal Consuderations

Shutdown Pin Operation

LOAD =

( 1-D ) x ( I

SW (max) -

)

D ( V

IN-VSW )

2fL

At higher duty cycles, the increased ON time of the

FET means the maximum output current will be deter-

mined by power dissipation within the AME5145 FET

switch. The switch power dissipation from ON-state con-

duction is calculated by:

(SW) = D x IIND(AVE)2 x RDS(ON)

There will be some switching losses as well, so some

derating needs to be applied when calculating IC power

dissipation.

Inductor Suppliers

Recommended suppliers of inductors for this product

include, but are not limited to Sumida, Coilcraft, Panasonic,

TDK and Murata. When selecting an inductor, make cer-

tain that the continuous current rating is high enough to

avoid saturation at peak currents. A suitable core type

must be used to minimize core (switching) losses, and

wire power losses must be considered when selecting

the current rating.

The device is turned off by pulling the shutdown pin low.

If this function is not going to be used, the pin should be

tied directly to V

IN. If the SHDN function will be needed, a

pull-up resistor must be used to V

IN (approximately 50k-

100k recommended).

The EN pin must not be left

unterminated.

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