ILC7083/ILC7084
REV. 1.0.9 1/28/03 7
Maximum Output Current
The maximum output current available from the ILC7083/
ILC7084 is limited by the maximum package power dissipa-
tion as well as the device’s internal current limit. For a given
ambient temperature, TA, the maximum package power
dissipation is given by:
P
D(MAX)
= (T
J(MAX)
– T
A
) / θ
JA
where T
J(MAX)
= 150°C is the maximum junction tempera-
ture and θ
JA
= 333°C/W is the package thermal resistance.
For example at T
A
= 85°C ambient temperature, the maxi-
mum 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
ILC7083.
Figure 4. Basic Application Circuit for
Fixed Output Voltage Versions
Input Capacitor
An input capacitor C
IN
of value 1µF 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 capaci-
tor 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 capacitor 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 reg-
ulator’s output voltage by a couple of hundred millivolts then
the regulator may be damaged. This condition must be
avoided. In many applications a large value input capacitor,
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
Fairchild strongly recommends the use of low ESR
(equivalent series resistance) ceramic capacitors for C
OUT
and C
NOISE
. The ILC7083/ILC7084 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 capacitor may be used at the output.
Use of ceramic chip capacitors offer significant advantages
over tantalum capacitors. A ceramic capacitor is typically
cheaper than a tantalum capacitor, it usually has a smaller
footprint, lower height, and lighter weight than a tantalum
capacitor. Furthermore, unlike tantalum capacitors which are
polarized and can be damaged if connected incorrectly,
ceramic capacitors are non-polarized. Low value ceramic
chip capacitors with X5R or X7R dielectric are available in
the 100pF to 4.7µF range. Beware of using ceramic capaci-
tors with Y5V dielectric since their ESR increases signifi-
cantly at cold temperatures. Please see the table of
recommended ceramic capacitors for use at the output of
ILC7083/ILC7084.
Note: If a tantalum output capacitor is used then for stable
operation. We recommend a low ESR tantalum capacitor
with maximum rated ESR at or below 0.4Ω. Low ESR tanta-
lum capacitors, such as the TPS series from AVX Corpora-
tion (www.avxcorp.com) or the T495 series from Kemet
(www.kemet.com) may be used.
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 ILC7083/ILC7084 is
stable with no load.
Noise Bypass Capacitor
In low noise applications, the self noise of the ILC7083 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 ILC7083 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 applica-
tions where exceptionally low output noise is not required,
consider omitting the noise bypass capacitor altogether.
ILC7083
V
OUT
V
IN
C
OUT
SOT23-5
C
IN
ON
OFF
123
45
C
NOISE
