50/100mA SOT-23 CMOS RF LDO™ Regulators
Maximum Output Current
The maximum output current available from the ILC7080/81
is limited by the maximum package power dissipation as
well as the device’s internal current limit. For a given ambi-
ent temperature, T
A
, the maximum package power dissipa-
tion is given by:
P
D(max)
= (T
J(max)
- T
A
) /
θ
JA
where T
J(max)
= 150°C is the maximum junction temperature
and
θ
JA
= 333°C/W is the package thermal resistance. For
example at T
A
= 85°C ambient temperature, the maximum
package power dissipation is;
P
D(max)
= 195mW.
The maximum output current can be calculated from the fol-
lowing equation:
I
OUT(max)
< P
D(max)
/ (V
IN
- V
OUT
)
For example at V
IN
= 6V, V
OUT
= 5V and T
A
= 85°C, the
maximum output current is I
OUT(max)
< 195mA. At higher
output current, the die temperature will rise and cause the
thermal protection circuit to be enabled.
APPLICATION HINTS
Figure 4 shows the typical application circuit for the
ILC7080/81.
V
OUT
5
C
IN
, will hold V
IN
higher than V
OUT
and decay slower than
V
OUT
when the LDO is powered off.
Output Capacitor Selection
Impala strongly recommends the use of low ESR (equiva-
lent series resistance) ceramic capacitors for C
OUT
and
C
NOISE
. The ILC7080/81 is stable with low ESR capacitor
(as low as zero
Ω).
The value of the output capacitor should
be 1µF or higher. Either ceramic chip or a tantalum capaci-
tor may be used at the output.
Use of ceramic chip capacitors offer significant advantages
over tantalum capacitors. A ceramic capacitor is typically
considerably cheaper than a tantalum capacitor, it usually
has a smaller footprint, lower height, and lighter weight than
a tantalum capacitor. Furthermore, unlike tantalum capaci-
tors which are polarized and can be damaged if connected
incorrectly, ceramic capacitors are non-polarized. Low
value ceramic chip capacitors with X7R dielectric are avail-
able in the 100pF to 4.7µF range, while high value capaci-
tors with Y5V dielectric are available in the 2200pF to 22µF
range. Evaluate carefully before using capacitors with Y5V
dielectric because their ESR increases significantly at cold
temperatures. Figure 10 shows a list of recommended
ceramic capacitors for use at the output of ILC7080/81.
Note:
If a tantalum output capacitor is used then for stable opera-
tion Impala recommends a low ESR tantalum capacitor with max-
imum rated ESR at or below 0.4Ω. Low ESR tantalum capacitors,
such as the TPS series from AVX Corporation (www.avxcorp.com)
or the T495 series from Kemet (www.kemet.com) may be used.
SOT23-5
4
ILC7080
ILC7081
C
NOISE
3
C
OUT
V
IN
1
2
In applications where a high output surge current can be
expected, use a high value but low ESR output capacitor for
superior load transient response. The ILC7080/81 is stable
with no load.
Noise Bypass Capacitor
In low noise applications, the self noise of the ILC7080/81
can be decreased further by connecting a capacitor from
the noise bypass pin (pin 4) to ground (pin 2). The noise
bypass pin is a high impedance node as such, care should
be taken in printed circuit board layout to avoid noise pick-
up from external sources. Moreover, the noise bypass
capacitor should have low leakage.
Noise bypass capacitors with a value as low as 470pF
may be used. However, for optimum performance, use a
0.01µF or larger, ceramic chip capacitor. Note that the turn
on and turn off response of the ILC7080/81 is inversely
proportional to the value of the noise bypass capacitor.
For fast turn on and turn off, use a small value noise
bypass capacitor. In applications were exceptionally low
output noise is not required, consider omitting the noise
bypass capacitor altogether.
ON
OFF
Figure 4: Basic application circuit for fixed output voltage versions
Input Capacitor
An input capacitor C
IN
of value 1mF or larger should be con-
nected from V
IN
to the main ground plane. This will help to
filter supply noise from entering the LDO. The input capac-
itor should be connected as close to the LDO regulator
input pin as is practical. Using a high-value input capacitor
will offer superior line transient response as well as better
power supply ripple rejection. A ceramic or tantalum capac-
itor may be used at the input of the LDO regulator.
Note that there is a parasitic diode from the LDO regulator
output to the input. If the input voltage swings below the
regulator’s output voltage by a couple of hundred milivolts
then the regulator may be damaged. This condition must be
avoided. In many applications a large value input capacitor,
Impala Linear Corporation
ILC7080/81 1.1
(408) 574-3939
www.impalalinear.com
Sept. 1998
7
IMPALA [ Impala Linear Corporation ]
