MIC5159_06 Datasheet, PDF (9/23 Pages) Micrel Semiconductor – Programmable Current Limit μCap LDO Regulator Controller

Micrel, Inc.
Input Capacitor
An input capacitor of 1.0µF or greater is recommended
when the device is more than 4 inches away from the
bulk AC supply capacitance or when the supply is a
battery. Small, surface mount, ceramic capacitors can be
used for bypassing the input to the regulator, further
improving the integrity of the output voltage. Larger input
capacitors may be required depending on the
impedance of the source and the output load
requirements.
Layout Considerations
Input and output capacitor placement should be as close
as possible to the input and output, respectively. Trace
resistance between the current sense and the MOSFET
source should be minimized. Trace resistance will
increase dropout voltage. This is more of a factor at
higher output currents.
Also, a minimum amount of distance between the gate
pin, on the MIC5159, and the P-Channel MOSFET gate
is recommended. A long trace can create a small
parasitic inductor. This, coupled to the gate capacitance
of the MOSFET, can create a high frequency tank circuit.
A small 50Ω resistor in series with the gate may be
required to eliminate high-frequency noise.
MIC5159
Adjustable Regulator Design
The MIC5159 allows programming the output voltage
anywhere between 1.235V to V_IN. Two resistors are
used. See Figure 4. The resistor values are calculated
by:
R1
=
R2
×
⎜⎜⎝⎛ ⎜⎜⎝⎛
V_OUT
1.235
⎟⎟⎠⎞
−
1_{⎟⎟⎠⎞}
Where V_OUT is the desired output voltage.
V_IN
R_S
Si3445
V_OUT
MIC5159-x.x
IS
GATE
IN
ADJ
EN _GND
C_OUT = 10µF
R1 ceramic
R2
Figure 4. Adjustable Regulator Design
June 2006
9
M9999-062706