MIC5232_08 Datasheet, PDF (8/10 Pages) Micrel Semiconductor – 10mA Ultra-Low Quiescent Current μCap LDO

Micrel, Inc.
Application Information
Input Capacitor
If there is more than 20cm of wire between IN and the
ac filter capacitor or if supplied from a battery, a 1µF
(or larger) capacitor should be placed from the IN
(supply input) to GND (ground).
Output Capacitors
The MIC5232 requires an output capacitor for stability.
A 0.47µF, or larger capacitor, is recommended
between OUT (output) and GND to improve the
regulator’s transient response. A 0.47µF 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 the
high frequency transient response. The value of this
capacitor 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.
Minimum Load Current
The MIC5232 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 MIC5232 incorporates current limit in the design.
There is also reverse circuit protection circuitry built
into the device. 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 MIC5232 is designed to provide 10mA of
continuous current in a very small package. Maximum
ambient operating temperature can be calculated
based on the output current and the voltage drop
across the part. Given that the input voltage is 4.3V,
the output voltage is 3.3V and the output current =
10mA.
The actual power dissipation of the regulator circuit
can be determined using the equation:
P_D = (V_IN – V_OUT) I_OUT + V_IN I_GND
Because this device is CMOS and the ground current
is typically <15μA over the load range, the power
dissipation contributed by the ground current is < 1%
and can be ignored for this calculation.
MIC5232
P_D = (4.3V – 3.3V) • 10mA
P_D = 0.01W
To determine the maximum ambient operating
temperature of the package, use the junction-to-
ambient thermal resistance of the device and the
following basic equation:
P_D(max)
=
T_J(max) − T_A
θ _JA
T_J(max) = 125°C, the max. junction temperature of the
die, θ_JA thermal resistance = 90°C/W
Table 1 shows junction-to-ambient thermal resistance
for the MIC5232 in the 2mm x 2mm MLF^®-6 package.
Package
2mm x 2mm MLF^®-6
θJA Recommended
Minimum Footprint
90°C/W
θJC
2°C/W
Table 1. MLF Thermal Resistance
Substituting PD for PD(max), and solving for the
ambient operating temperature, will give the maximum
operating conditions for the regulator circuit. The
junction-to-ambient thermal resistance for the
minimum footprint is 90°C/W, from Table 1. The
maximum power dissipation must not be exceeded for
proper operation.
For example, when operating the MIC5232-3.3BML at
an input voltage of 4.3V and 10mA load with a
minimum footprint layout, the maximum ambient
operating temperature TA can be determined as
follows:
0.01W = ^{125°C − TA}
90°C / W
T_A = 124°C
Therefore, a 3.3V application at 10mA of output
current can accept an ambient operating temperature
of 124°C in a 2mm x 2mm MLF^®-6 package. For a full
discussion of heat sinking and thermal effects on
voltage regulators, refer to the “Regulator Thermals”
section of Micrel’s “Designing with Low-Dropout
Voltage Regulators” handbook. This information can
be found on Micrel's website at:
http://www.micrel.com/_PDF/other/LDOBk_ds.pdf
September 2008
8
M9999-090508-C