PRELIMINARY
CM3015
Application Information
VIN=VOUT
+
VOUT=VSENSE (1+R1/R2)
VOUT
4.992V
RDROP(IOUT
)
=
1
2
3
V
V
6
5
4
IN
OUT
R1
31.6k
1.20V
GND SENSE
R2
10.0k
EN
BYP
For the input voltage, Vin minimum will depend on the output current. For
example, if Iout is 100mA, Vin must be at least 4.992V = 1ohm x 100mA =
4.992 + 0.1 = 5.092V.
Figure 32. Adjustable Regulator Application Example
Output Compensation
Low-dropout regulator topologies use a current-carry-
ing transistor ("pass device") that adds additional gain
and phase shift to the design. It is necessary to com-
pensate for these attributes to prevent the design from
becoming unstable. The simplest way to do this is to
add an output RC filter to roll off the gain. Since all reg-
ulators use an output capacitor anyway, the only com-
ponent needed is a suitable resistance. Fortunately, for
the usual range and types of output capacitors, this
resistance can be supplied by the ESR of the caps.
An attribute of the LDO topology is that the pass device
gain generally increases with increasing output current.
This may affect output stability: a design that didn't
need a capacitor now does, or a design that used a
small value now needs a larger one. The CMD advan-
tage is that this component can be selected from any
capacitor family without regard to its ESR. If the circuit
calls for a tiny, low-ESR capacitor, it will work just fine.
For many years, capacitors have been the largest com-
ponents in regulator circuits, but newer types are
shrinking in size rapidly. Unfortunately, their ESRs
have shrunk as well, taking them out of the range
where they can perform the R function described in
existing LDOs. The CM3015 is a new breed of LDO
regulator that can work with these tiny low-ESR capac-
itors and thus permit designs that take a minimum of
space.
© 2004 California Micro Devices Corp. All rights reserved.
09/14/04 430 N. McCarthy Blvd., Milpitas, CA 95035-5112
●
Tel: 408.263.3214
●
Fax: 408.263.7846
●
www.calmicro.com 11
CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
