MIC5350 MICREL [Micrel Semiconductor], MIC5350 Datasheet - Page 8

• Manufacturer Part Number: MIC5350
• Manufacturer: MICREL [Micrel Semiconductor]

Applications Information
Enable/Shutdown
The MIC5350 comes with dual active-high enable pins
that allow each regulator to be enabled independently.
Forcing both enable pins low disables the regulators 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; a floating enable
pin may cause an indeterminate state on the output.
Input Capacitor
The MIC5350 is a high-performance, high-bandwidth
device. Therefore, it requires a well-bypassed input
supply for optimal performance. A 2.2µF capacitor is
required from the input to ground to provide stability.
Low-ESR
performance at a minimum of space. Additional high-
frequency capacitors, such as small-valued NPO
dielectric-type capacitors, help filter out high-frequency
noise and are good practice in any RF-based circuit.
Output Capacitor
The MIC5350 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
recommended because of their superior 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
an X7R ceramic capacitor to ensure the same minimum
capacitance over the equivalent operating temperature
range.
Bypass Capacitor
A capacitor can be placed from the noise 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 capacitor can be increased, further
reducing noise and improving PSRR. Turn-on time
increases slightly with respect to bypass capacitance.
Micrel, Inc.
June 2010
dielectric-type
ceramic
capacitors
ceramic
provide
capacitors
optimal
are
8
A unique, quick-start circuit allows the MIC5350 to drive
a large capacitor on the bypass pin without significantly
slowing turn-on time.
No-Load Stability
Unlike many other voltage regulators, the MIC5350 will
remain stable with no load. This is especially important
in CMOS RAM keep-alive applications.
Thermal Considerations
The MIC5350 is designed to provide 300mA of
continuous current for V
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 3.3V, the output voltage is 2.8V for
V
500mA respectively. The actual power dissipation of the
regulator circuit can be determined using the equation:
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.
To
temperature of the package, use the junction-to-ambient
thermal resistance of the device and the following basic
equation:
T
the die θ
J(max)
OUT1
, 2.8V for V
determine
= 125°C, the maximum junction temperature of
P
I
P
500mA
P
P
GND
JA
D
D
D
D(MAX)
thermal resistance = 90°C/W.
= (V
= (3.3V – 2.8V) × 300mA + (3.3V -2.8) ×
= 0.4W
IN
=
OUT2
– V
the
⎝
⎛
OUT1
and the output current 300mA and
T
J(MAX)
maximum
) I
OUT1
OUT1
JA
and 500mA for V
- T
+ (V
A
IN
ambient
– V
OUT2
M9999-060410
) I
MIC5350
OUT2
operating
OUT2
+ V
in a
IN