MIC68400 Datasheet, PDF (10/15 Pages) Micrel Semiconductor – 4A Sequencing LDO with Tracking and Ramp Control™

Micrel, Inc.
Applications Information
Enable Input
The MIC68400 features a TTL/CMOS compatible
positive logic enable input for on/off control of the
device. High (>1V) enables the regulator while low
(<.2V) disables the regulator. In shutdown the
regulator consumes very little current (only a few
microamperes of leakage). For simple applications the
enable (EN) can be connected to V_IN (IN). While
MIC68400 only requires a few µA’s of enable current
to turn on, actual enable pin current will depend on the
overdrive (enable voltage exceeding 1V) in each
particular application.
Control Logic
High > 1V
Enable Connections for Logic Driven Input
MIC68400
Input Capacitor
An input capacitor of 0.1µF or greater is
recommended when the device is more than 4 inches
away from the bulk supply capacitance, or when the
supply is a battery. Small, surface mount chip capac-
itors can be used for the bypassing. The capacitor
should be place within 1 inch of the device for optimal
performance. Larger values will help to improve ripple
rejection by bypassing the regulator input, further
improving the integrity of the output voltage.
Output Capacitor
The MIC68400 requires an output capacitor for stable
operation. As a µCap LDO, the MIC68220 can
operate with ceramic output capacitors of 10µF or
greater with ESR’s ranging from a 3mΩ to over
300mΩ. Values of greater than 10µF improve trans-
ient response and noise reduction at high frequency.
X7R/X5R dielectric-type ceramic capacitors are
recommended because of their superior temperature
performance. X7R-type capacitors change capaci-
tance by 15% over their operating temperature range
and are the most stable type of ceramic capacitors.
Larger output capacitances can be achieved by
placing tantalum or aluminum electrolytics in parallel
with the ceramic capacitor. For example, a 100µF
electrolytic in parallel with a 10µF ceramic can provide
the transient and high frequency noise performance of
a 100µF ceramic at a significantly lower cost. Specific
undershoot/overshoot performance will depend on
both the values and ESR/ESL of the capacitors.
Enable Connection for V_IN-Driven
and/or Slow Rise-Time Inputs
September 2007
10
M9999-090607-C