MIC5231(2000) Просмотр технического описания (PDF) - Micrel
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MIC5231 Datasheet PDF : 8 Pages
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MIC5231
Block Diagram
IN
OUT
EN
MIC5231
Bandgap
Reference
GND
Micrel
Applications Information
Input Capacitor
A 0.1µF (or larger) capacitor should be placed from the IN
(supply input) to GND (ground) if there is more than 20 cm of
wire between IN and the ac filter capacitor or if supplied from
a battery.
Output Capacitors
The MIC5231 does not require an output capacitor for stabil-
ity. A 1µF or larger capacitor is recommended between OUT
(output) and GND to improve the regulator’s transient re-
sponse. A 0.1µF capacitor can be used to reduce overshoot
recovery time at the expense of overshoot amplitude. The
ESR (effective series resistance) of this capacitor has no
effect on regulator stability, but low-ESR capacitors improve
high frequency transient response. The value of this capaci-
tor may be increased without limit, but values larger than
10µF tend to increase the settling time after a step change in
input voltage or output current.
The MIC5231 has no minimum load current; it will remain
stable and in regulation with no load (other than the internal
voltage divider). This is especially important in real-time clock
and CMOS RAM keep-alive applications.
Minimum Load Current
The MIC5231 does not require a minimum load for proper
operation. This allows the device to operate in applications
where very light output currents are required for keep-alive
purposes. This is important for powering SRAM or Flash
memory in low-power modes for handheld devices.
Safe Operating Conditions
The MIC5231 does not incorporate current limit or thermal
shutdown in the design. The output pass element is approxi-
mately 15 ohms, therefore, when a short occurs from the
output to ground, the current is self-limited. The pass element
has a positive temperature coefficient, such that when the
device gets hot, the output impedance goes up, limiting the
current even further. The maximum junction temperature for
the device is 125°C, and it is important that this is not
exceeded for any length of time.
Thermal Considerations
The MIC5231 is not intended for sourcing currents that would
cause a large power loss in the device, but since it is not
current limited, it is possible to source more than the rated
10mA. At this point, it is important to ensure that the die
temperature does not exceed 125°C.
Power dissipation in the regulator is calculated as follows:
PD = (VIN – VOUT)*IOUT+ VIN *IGND
The MIC5231 consumes only 0.65uA over load and does not
need to consider that contribution in the power dissipation
equation, therefore the equation is simplified.
PD = (VIN – VOUT )*IOUT
The MIC5231, in the IttyBitty SOT23-5 package, has a
thermal resistance, junction-to-ambient, of 235°C/W. Using
this number, the power dissipation capability of that package,
without exceeding a 125°C junction temperature rating, can
easily be calculated.
PD(max) = (Tj(max) – Ta)/θJA
PD(max) = (125°C – Ta)/235°C/W
If the device is being operated at 85°C, the maximum power
June 2000
5
MIC5231
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