MIC5156-3.3BN View Datasheet(PDF) - Micrel
Part Name
Description
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MIC5156-3.3BN Datasheet PDF : 13 Pages
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MIC5156/5157/5158
VIN
G
MIC5157
or
S
MIC5158
EA
GND
Micrel, Inc.
Adjustable Configurations
Micrel’s MIC5156 [adjustable] and MIC5158 require an ex-
ternal resistive divider to set the output voltage from 1.235V
to 36V. For best results, use a 10kΩ resistor for R2. See
equation (1) and figure (2).
( ) 1)
R1 = 1 × 104
VOUT
1.235
-1
Figure 1b. Connections for Adjustable Output
G
MIC5156
EA
GND
VIN
*
* Optional 16V zener diode
recommended in applications
where VG is greater than 18V
Figure 1c. MIC5156 Connections for
Adjustable Output
MOSFET Gate-to-Source Protection
When using the adjustable version of the MIC5156, an external
16V zener diode placed from gate-to-source is recommended
for MOSFET protection. All other versions of the Super LDO
regulator controller use the internal gate-to-source clamp.
Output Voltage Configuration
Fixed Configurations
The MIC5156-3.3 and MIC5156-5.0 are preset for 3.3V and
5.0V respectively.
The MIC5157 operates at 3.3V when the 3.3V pin is connected
to the S (source) pin; 5.0V when the 5.0V pin is connected to
the S pin; or 12V if the 3.3V and 5.0V pins are open.
The MIC5158 operates at a fixed 5V (without an external
resistive divider) if the 5V FB pin is connected to EA.
G
S
MIC5157/8
EA*
GND
VO U T
R1
R2
10k
Figure 2. Typical Resistive Divider
Input Filter Capacitor
The Super LDO requires an input bypass capacitor for accom-
modating wide changes in load current and for decoupling
the error amplifier and charge pump. A medium to large value
low-ESR (equivalent series resistance) capacitor is best,
mounted close to the device.
Output Filter Capacitor
An output filter capacitor may be used to reduce ripple and
improve load regulation. Stable operation does not require
a large capacitor, but for transient load regulation the size of
the output capacitor may become a consideration. Common
aluminum electrolytic capacitors perform nicely; very low-ESR
capacitors are not necessary. Increased capacitance (rather
than reduced ESR) is preferred. The capacitor value should
be large enough to provide sufficient I = C × dV/dt current
consistent with the required transient load regulation quality.
For a given step increase in load current, the output voltage will
drop by about dV = I × dt/C, where I represents the increase
in load current over time t. This relationship assumes that
all output current was being supplied via the MOSFET pass
device prior to the load increase. Small (0.01µF to 10µF) film
capacitors parallel to the load will further improve response
to transient loads.
Some linear regulators specify a minimum required output filter
capacitance because the capacitor determines the dominant
pole of the system, and thereby stabilizes the system. This
is not the situation for the MIC5156/7/8; its dominant pole is
determined within its error amplifier.
August 2005
9
MIC5156/5157/5158
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