MIC5249-1.8YMM Micrel Inc, MIC5249-1.8YMM Datasheet - Page 5

• Manufacturer Part Number: MIC5249-1.8YMM
• Description: 300mA UCapl LDO With Reset( )
• Manufacturer: Micrel Inc

Specifications of MIC5249-1.8YMM

• Regulator Topology: Positive Fixed
• Voltage - Output: 1.8V
• Voltage - Input: 2.7 ~ 6 V
• Voltage - Dropout (typical): 0.34V @ 300mA
• Number Of Regulators: 1
• Current - Output: 300mA
• Current - Limit (min): 300mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application Information
Enable/Shutdown
The MIC5249 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. This part is CMOS
and the enable pin cannot be left floating; a floating
enable pin may cause an indeterminate state on the
output.
Input Capacitor
The MIC5249 is a high performance, high bandwidth
device. Therefore, it requires a well-bypassed input
supply for optimal performance. A 1.0µF capacitor is
required from the input to ground to provide stability.
Low-ESR ceramic capacitors provide optimal perform-
ance at a minimum of space. Additional high-frequency
capacitors such as small valued NPO dielectric type
capacitors help to filter out high frequency noise and are
good practice in any RF-based circuit.
Output Capacitor
The MIC5249 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 300mΩ. 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 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 anX7R
ceramic capacitor to ensure the same minimum
capacitance over the equivalent operating temperature
range.
Delay Pin Input
The power-on reset function can be implemented on the
MIC5249 by adding an external capacitor from the delay
pinto ground. This external capacitor sets the delay time
(TDELAY) of the RESET output. The capacitor value
required can be easily calculated using the formula:
Micrel, Inc.
September 2006
5
where IDELAY is 0.55µA and the VDELAY is 1.4V.
When no capacitor is used, there will be no delay and
the POR output acts like a standard error FLAG output.
Reset Output
The RESET output of the MIC5249 provides the power-
on reset signal based on the capacitor from the DELAY
pin to ground when input power is applied to the
regulator. The reset signal stays low for a preset time
period after power is applied to the regulator, and then
goes high (see “Timing Diagram”).
The reset output is an active-low, open-drain output that
drives low when a fault condition AND an undervoltage
detection occurs. Internal circuitry intelligently monitors
overcurrent, overtemperature and dropout conditions
and ORs these outputs together to indicate some fault
condition. The output of that OR gate is ANDed with an
output voltage monitor that detects an undervoltage
condition. The output drives an open-drain transistor to
indicate a fault. This prevents chattering or inadvertent
triggering of the reset. There set must be pulled up using
a resistor form the RESET pin to either the input or the
output.
Bypass Pin Input
A bypass capacitor is required from the noise bypass pin
to ground to reduce output voltage noise. The capacitor
bypasses the internal reference. A 0.01µF 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. A
unique quick-start circuit allows the MIC5249 to drive a
large capacitor on the bypass pin without significantly
slowing the turn-on time.
Active Shutdown
The MIC5249 also features an active shutdown clamp,
which is a N-Channel MOSFET that turns on when the
device is disabled. This allows the output capacitor and
load to discharge, de-energizing the load.
No-Load Stability
The MIC5249 will remain stable and in regulation with no
load unlike many other voltage regulators. This is
especially
application.
C
DELAY
important
=
⎛
⎜ ⎜
⎝
T
DELAY
V
in
DELAY
×
I
DELAY
CMOS
⎞
⎟ ⎟
⎠
RAM
M9999-090806
MIC5249
keep-alive