AME, Inc.
AME5140
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Application Hints
Feed-Forward Compensation
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:
1.6 MHz Boost Converter With
30V Internal FET Switch
Layout Hints
Cf = 1 / (2 x
π
x R1 x fz)
Selecting Diodes
The external diode used in the typical application should
be a Schottky diode. A 20V diode such as the MBR0520
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.
Layout Hints
High frequency switching regulators require very care-
ful layout of components in order to get stable operation
and low noise. All components must be as close as pos-
sible to the AME5140 device. It is recommended that a
4-layer PCB be used so that internal ground planes are
available. As an example, a recommended layout of com-
ponents is shown:
Recommended PCB Component Layout (Bottom)
Some additional guidelines to be observed:
1. Keep the path between L1, D1, and C2 extremely
short. Parasitic trace inductance in series with D1 and C2
will increase noise and ringing.
2. The feedback components R1, R2 and CF must be
kept close to the FB pin of U1 to prevent noise injection
on the FB pin trace.
3. If internal ground planes are available use vias to con-
nect directly to ground at pin 2 of U1, as well as the nega-
tive sides of capacitors C1 and C2.
Duty Cycle
The maximum duty cycle of the switching regulator de-
termines the maximum boost ratio of output-to-input volt-
age that the converter can attain in mode of operation.
The duty cycle for a given boost application is defined as:
This applies for continuous mode operation.
D=
Recommended PCB Component Layout (Top)
V
OUT
+ V
DIODE
- V
IN
V
OUT
+ V
DIODE
- V
SW
Rev.G.01
11
AME [ ANALOG MICROELECTRONICS ]
