MIC5319 Datasheet, PDF (8/10 Pages) Micrel Semiconductor – 500mA uCap Ultra-Low Dropout, High PSRR LDO Regulator

MIC5319
Applications Information
Enable/Shutdown
The MIC5319 features 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. The active-high enable pin uses CMOS
technology and the enable pin cannot be left floating, as this
may cause an indeterminate state on the output.
Input Capacitor
The MIC5319 is a high-performance, high bandwidth device.
Therefore, it requires a well-bypassed input supply for opti-
mal performance. A 1µF capacitor is required from the input-
to-ground to provide stability. Low-ESR ceramic capacitors
provide optimal performance at a minimum of space. Addi-
tional high frequency capacitors, such as small-valued NPO
dielectric-type capacitors, help filter out high-frequency noise
and are good design practice in any RF-based circuit.
Output Capacitor
The MIC5319 requires an output capacitor of 2.2µF or greater
to maintain stability. The design is optimized for use with low-
ESR ceramic chip capacitors. High ESR capacitors may
cause high frequency oscillation. The output capacitor can be
increased, but performance has been optimized for a 2.2µF
ceramic output capacitor and does not improve significantly
with larger capacitance.
X7R/X5R dielectric-type ceramic capacitors are recom-
mended because of their temperature performance. X7R-
type capacitors change capacitance by 15% over their oper-
ating 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 capaci-
tor with Y5V dielectric, the value must be much higher than an
X7R ceramic capacitor to ensure the same minimum capaci-
tance over the equivalent operating temperature range.
Bypass Capacitor
A capacitor can be placed from the bypass pin-to-ground to
reduce output voltage noise. The capacitor bypasses the
internal reference. A 0.1µF capacitor is recommended for
applications that require low-noise outputs. The bypass ca-
pacitor can be increased, further reducing noise and improv-
ing PSRR. Turn-on time increases slightly with respect to
bypass capacitance. A unique, quick-start circuit allows the
MIC5319 to drive a large capacitor on the bypass pin without
significantly slowing turn-on time. Refer to the “Typical Char-
acteristics” section for performance with different bypass
capacitors.
Micrel
No-Load Stability
Unlike many other voltage regulators, the MIC5319 will
remain stable and in regulation with no load. This is especially
important in CMOS RAM keep-alive applications.
Adjustable Regulator Application
Adjustable regulators use the ratio of two resistors to multiply
the reference voltage to produce the desired output voltage.
The MIC5319 can be adjusted from 1.25V to 5.5V by using
two external resistors (Figure 1). The resistors set the output
voltage based on the following equation:
V_OUT = V_REF ^{⎛⎝⎜}1+ _RR21^{⎞⎠⎟}
V_REF = 1.25V
MIC5319BML
V_IN
VIN VOUT
EN
1µF
BYP ADJ
GND
V_OUT
R1
2.2µF
R2
Figure 1. Adjustable Voltage Application
Thermal Considerations
The MIC5319 is designed to provide 500mA of continuous
current in a very small MLF package. Maximum ambient
operating temperature can be calculated based on the output
current and the voltage drop across the part. Given an input
voltage of 3.3V, output voltage of 2.8V and output current =
500mA, 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 <100µA over the load range, the power dissipation
contributed by the ground current is < 1% and can be ignored
for this calculation.
P_D = (3.3V – 2.8V) × 500mA
P_D = 0.25W
To determine the maximum ambient operating temperature
of the package, use the junction-to-ambient thermal resis-
tance of the device and the following basic equation:
P_D(max)
=
⎛
⎝⎜
T_J
(max)
θ _JA
–
T_A
⎞
⎠⎟
T_J(max) = 125°C, the maximum junction temperature of the die
θ_JA thermal resistance = 93°C/W
October 2004
8
M9999-100604