AME, Inc.
AME5140
n
Application Hints
Calculating Load Current
The load current is related to the average inductor cur-
rent by the relation:
I
LOAD
= I
IND
(AVG) x (1 - D)
Where
“D”
is the duty cycle of the application. The
switch current can be found by:
I
SW
= I
IND
(AVG) + 1 /2 (I
RIPPLE
)
Inductor ripple current is dependent on inductance, duty
cycle, input voltage and frequency:
I
RIPPLE
= D x (V
IN
-V
SW
) / (f x L)
Combining all terms, we can develop an expression
which allows the maximum available load current to be
calculated:
Shutdown Pin Operation
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.
1.6 MHz Boost Converter with
30V Internal FET Switch
I
LOAD
=
( 1-D ) x ( I
SW
(max) -
Thermal Consuderations
D ( V
IN
-V
SW
)
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 AME5140 FET
switch. The switch power dissipation from ON-state con-
duction is calculated by:
P
(SW)
= D x I
IND(AVE)2
x R
DS
(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.
12
Rev.G.01
AME [ ANALOG MICROELECTRONICS ]
