AME
1.4MHz Boost Converter with
30V Internal FET Switch
AME5143
n Application Hints
Feed-Forward Compensation
Shutdown Pin Operation
Although internally compensated, the feed-forward ca-
pacitor Cf is required for stability. Adding this capacitor
puts a zero in the loop response of the Converter. The
recommended frequency for the zero fz should be ap-
proximately 6kHz. Cf can be calculated using the for-
mula:
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 VIN. If the SHDN function will be needed, a
pull-up resistor must be used to VIN (approximately 50k-
100k recommended). The EN pin must not be left
unterminated.
Cf = 1 / (2 x p x R1 x fz)
Selecting Diodes
The external diode used in the typical application should
be a Schottky diode. A 30V diode such as the MBR0530
is recommended. The MBR05XX series of diodes are
designed to handle a maximum average current of 0.5A.
For applications exceeding 0.5A average but less than
1A, a Microsemi UPS5817 can be used.
Thermal Consuderations
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 AME5143 FET
switch. The switch power dissipation from ON-state con-
duction is calculated by:
P(SW) = D x I2IND(AVE)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.
Rev.A.01
10
AME [ ANALOG MICROELECTRONICS ]
