AMS2931 Ver la hoja de datos (PDF) - Advanced Monolithic Systems Inc
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AMS2931 Datasheet PDF : 9 Pages
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TYPICAL PERFORMANCE CHARACTERISTICS (Continued)
AMS2931
Maximum Power Dissipation (TO-263)
4 θJA = 32° C/W
3
θJA = 37° C/W
2
θJA = 50° C/W
1
θJA = 73° C/W
0
0 10 20 30 40 50 60 70 80 90 100
AMBIENT TEMPERATURE (° C)
On/Off Treshold
4.0
3.8 AMS2931C ADJUSTABLE
3.6
3.4
3.2
OFF
3.0
2.8
2.6
ON
2.4
2.2
2.0
0
3 6 9 12 15 18 21 24
OUTPUT VOLTAGE (V)
Output Capacitor ESR
100
COUT= 100µF
VO = 5V
10
1
STABLE
0.1
REGION
0.01
0
20 40 60 80 100
OUTPUT CURRENT (mA)
APPLICATION HINTS
The AMS2931 series require an output capacitor for device
stability. The value required depends on the application circuit and
other factors.
Because high frequency characteristics of electrolytic capacitors
depend greatly on the type and even the manufacturer, the value of
capacitance that works well with AMS2931 for one brand or type
may not necessary be sufficient with an electrolytic of different
origin. Sometimes actual bench testing will be the only means to
determine the proper capacitor type and value. To obtain stability
in all general applications a high quality 100µF aluminum
electrolytic or a 47µF tantalum electrolytic can be used.
A critical characteristic of the electrolytic capacitors is their
performance over temperature. The AMS2931 is designed to
operate to -40°C, but some electrolytics will freeze around -30°C
therefore becoming ineffective. In such case the result is
oscillation at the regulator output. For all application circuits
where cold operation is necessary, the output capacitor must be
rated to operate at the minimum temperature. In applications
where the regulator junction temperature will never be lower than
25°C the output capacitor value can be reduced by a factor of two
over the value required for the entire temperature range (47µF for
a high quality aluminum or 22µF for a tantalum electrolytic
capacitor).
With higher output currents, the stability of AMS2931 decreases.
Considering the fact that in many applications the AMS2931 is
operated at only a few milliamps (or less) of output current, the
output capacitor value can be reduced even further. For example, a
circuit that is required to deliver a maximum of 10mA of output
current from the regulator output will need an output capacitor of
only half the value compared to the same regulator required to
deliver the full output current of 100mA.
In the case of AMS2931C (adjustable), the minimum value of
output capacitance is a function of the output voltage. As a general
rule, with higher output voltages the value of the output
capacitance decreases, since the internal loop gain is reduced.
In order to determine the minimum value of the output capacitor,
for an application circuit, the entire circuit including the capacitor
should be bench tested at minimum operating temperatures and
maximum operating currents. To maintain internal power
dissipation and die heating to a minimum, the input voltage should
be maintain at 0.6V above the output. Worst-case occurs just after
input power is applied and before the die had the chance to heat
up. After the minimum capacitance value has been found for the
specific brand and type of electrolytic capacitor, the value should
be doubled for actual use to cover for production variations both
in the regulator and the capacitor.
www.advanced-monolithic.com
updated April 24, 2009
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