ame5248a AME, Inc., ame5248a Datasheet - Page 11

• Manufacturer Part Number: ame5248a
• Description: Synchronous Buck Converter
• Manufacturer: AME, Inc.

AME5248A
Rev.A.01
Output Capacitor Selection
series resistance (ESR). Typically, once the ESR re-
quirement for C
generally far exceeds the I
output ripple V
tance and
output voltage, the output ripple is highest at maximum
input voltage since
Saving Mode, and the output voltage ripple is indepen-
dent of the value of the output capacitor. The output ripple
is set by the internal comparator thresholds and is also
affected by the feedback capacitor C1 in figure2. Large
capacitor values can decrease the output ripple, usually
a 22pF capacitor is sufficient for most applications.
sen, choose the X5R or X7R dielectric formulations. These
dielectrics have the best temperature and voltage char-
acters have the best temperature and voltage character-
istics of all the ceramics for a given value and size.
resistor divider according to following formula:
The external resistor divider is connected to the output.
V
Output Voltage Setting
OUT
The selection of C
At the light load current, the device operates in Power
When the input and output ceramic capacitors are cho-
In the adjustable version, the output voltage is set by a
V
Where f
OUT
0
5 .
△
SW
V
I
AME
I
L
=operating frequency, C
L
=ripple current in the inductor. For a fixed
(
OUT
OUT
ESR
1 (
is determined by
has been met, the RMS current rating
△
OUT
R
R
I
1
2
L
8
is driven by the required effective
)
increases with input voltage.
C
OUT
RIPPLE
1
f
SW
(P-P) requirement. The
)
OUT
=output capaci-
Thermal Considerations
pate much heat due to its high efficiency. But, in applica-
tions where the AME5248A is running at high ambient
temperature with low supply voltage and high duty cycles,
such as in dropout, the heat dissipated may exceed the
maximum junction temperature of the part. If the junc-
tion temperature reaches approximately 160
power switches will be turned off and the SW node will
become high impedance. To avoid the AME5248A from
exceeding the maximum junction temperature, the user
will need to do some thermal analysis. The goal of the
thermal analysis is to determine whether the power dis-
sipated exceeds the maximum junction temperature of
the part. The temperature rise is given by:
to the ambient temperature.
J
In most applications the AME5248A does not dissi-
Where PD is the power dissipated by the regulator and
A
TR
Synchronous Buck Converter
is the thermal resistance from the junction of the die
(
PD
)
JA
1.5MHz, 600mA
℃
, both
11