MIC5295_09 Datasheet, PDF (8/11 Pages) Micrel Semiconductor – Low Quiescent Current, 150mA LDO Regulator

Micrel, Inc.
Application Information
Enable/Shutdown
The MIC5295 comes with an active-high enable pin that
allows the regulator to be disabled. Forcing the enable
pin low disables the regulator and sends it into a “zero”
off-mode-current state. In this state, current consumed
by the regulator goes nearly to zero. Forcing the enable
pin high enables the output voltage. Do not leave this pin
floating as the output will be in indeterminate state.
Input Capacitor
The MIC5295 has high input voltage capability up to
24V. The input capacitor must be rated to sustain
voltages that may be used on the input. An input
capacitor may be required when the device is not near
the source power supply or when supplied by a battery.
Small, surface mount, ceramic capacitors can be used
for bypassing. Larger values may be required if the
source supply has high ripple.
Output Capacitor
The MIC5295 requires an output capacitor for stability.
The design requires 2.2µF or greater on the output to
maintain stability. The design is optimized for use with
low-ESR ceramic chip capacitors. High ESR capacitors
may cause high frequency oscillation. The maximum
recommended ESR is 3Ω. The output capacitor can be
increased without limit. Larger valued capacitors help to
improve transient response.
X7R/X5R dielectric-type ceramic capacitors are
recommended because of their temperature
performance. X7R-type capacitors change capacitance
by 15% over their operating temperature range and are
the most stable type of ceramic capacitors. Z5U and
Y5V dielectric capacitors change value by as much as
50% and 60% respectively over their operating
temperature ranges. To use a ceramic chip capacitor
with Y5V dielectric, the value must be much higher than
a X7R ceramic capacitor to ensure the same minimum
capacitance over the equivalent operating temperature
range.
No-Load Stability
The MIC5295 will remain stable with no load unlike
many other voltage regulators. This is especially
important in CMOS RAM keep-alive applications.
Thermal Considerations
The MIC5295 is designed to provide 150mA of
continuous current in a small package. Maximum
ambient operating temperature can be calculated based
on the output current and the voltage drop across the
MIC5295
part. For example, given that the input voltage of 3.3V
the output voltage is 2.3V and the output current =
150mA. 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
Due to the potential for input voltages up to 24V, ground
current must be taken into consideration.
P_D(MAX) = (3.3 – 2.3V)150mA + 3.3x 1.2mA
P_D(MAX) = 0.154W
The junction-to-ambient thermal resistance for the
MIC5295, D-Pak is 50°C/W.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) −
θ _JA
T_A
⎟⎟⎠⎞
T_J(MAX) is the maximum junction temperature of the die,
125°C, the maximum ambient temperature can be
calculated to be 117.3°C as shown below:
0.154W = ⎜⎛ ^{125°C − TA} ⎟⎞
⎝ ^50°C/W ⎠
T_A = 117.3°C
Adjustable Regulator Application
The MIC5295YD can be adjusted from 1.24V to 20V by
using two external resistors (Figure 1). The resistors set
the output voltage based on the following equation:
V_OUT
=
V_REF
⎜⎜⎝⎛¹
+
⎜⎜⎝⎛
R₁
R₂
⎟⎟⎠⎞ _{⎟⎟⎠⎞}
Where V_REF = 1.24V.
Feedback resistor R2 should be no larger than 300kΩ.
Figure 1. Adjustable Voltage Application
November 2009
8
M9999-110209-A