Applications Information
Enable/ Shutdown
Forcing EN (enable/ shutdown) high (>2V) enables the regulator. EN is compatible with CMOS logic gates. If
enable shutdown feature is not required, connect EN (pin 3) to IN (supply input, pin 1). See Figure 3.
Input Capacitor
A 1µF capacitor should be placed from IN to GND if there is more than 10 inches of wire between the input
and the acfilter capacitor or if a battery is used as the input .
Reference Bypass Capacitor
BYP (reference bypass) is connected to the internal voltage reference. A 470pF capacitor (C
BYP
) connected
from BYP to GND quiets this reference, providing a significant reduction in output noise. C
BYP
reduces the
regulator phase margin, when using C
BYP
, output capacitors of 2.2µF or greater are generally required to
maintain stability.
The start-up speed of GM6155 is inversely proportional to the size of the reference bypass capacitor.
Applications requiring a slow ramp-up of output voltage should consider larger values of C
BYP
. Likewise, if
rapid turn-on is necessary, consider omitting C
BYP
.
If output noise is not a major concern, omit C
BYP
and leave BYP open.
Output Capacitor
An output capacitor required between OUT and GND to prevent oscillation. The minimum size of the output
capacitor is dependent upon whether a reference bypass capacitor is used. 1.0µF minimum is recommended
when C
BYP
is not used (see Figure 2). 2.2µF minimum is recommended when C
BYP
is 470pF (see Figure 1).
Larger values improve the regulator's transient response, the output capacitor value may be increased
without limit.
The output capacitor should have an ESR (effective series resistance) of about 5W or less and a resonant
frequency above 1MHz. Ultra-low-ESR capacitors can cause a low amplitude oscillation on the output and/
or underdamped transient response. Most tantalum or aluminum electrolytic capacitors are adequate; film
types will work, but more expensive. Since many aluminum electrolytics have electrolytes that freeze at
about -30°C, solid tantalums ate recommended for operation below -25°C.
At lower values for output current, less output capacitance is required for output stability. The capacitor can
be reduced to 0.47µF for current below 10mA or 0.33µF for current below 1mA.
No-Load Stability
GM6155 will remain stable and in regulation with no load (other than the internal voltage divider) unlike
many other voltage regulators. This is especially important in CMOS RAM keep-alive applications.
Thermal Considerations
Gm6155 is designed to provide 150mA of continuous current in a very small package. Maximum power
dissipation can be calculated based on the output current and the voltage drop across the part. To determine
the maximum power dissipation of the package, use the junction-to-ambient thermal resistance of the device
and the following basic equation:
P
D(max)
=
(T
J(max)
- T
A
)
R
q
JA
T
J(max)
is the maximum junction temperature of the die, 125°C, and T
A
is the ambient operating temperature.
R
qJA
is layout dependent; Table 1 shows examples of junction-to-ambient thermal resistance for the GM6155.
GM6155
5
GAMMA [ GAMMA MICROELECTRONICS INC. ]
