NCP605, NCP606
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10
APPLICATIONS INFORMATION
The NCP605/NCP606 regulator is self*protected with
internal thermal shutdown and internal current limit. Typical
application circuits are shown in Figures 1 to 4.
Input Decoupling (C
in
)
A ceramic or tantalum 1.0 mF capacitor is recommended
and should be connected close to the NCP605/NCP606
package. Higher capacitance and lower ESR will improve
the overall line transient response.
Output Decoupling (C
out
)
The NCP605/NCP606 is a stable component and does not
require a minimum Equivalent Series Resistance (ESR) for
the output capacitor. The minimum output decoupling value
is 1.0 mF and can be augmented to fulfill stringent load
transient requirements. The regulator works with ceramic
chip capacitors as well as tantalum devices. Larger values
improve noise rejection and load regulation transient
response. Typical characteristics were measured with
Murata ceramic capacitors. GRM219R71E105K (1 mF,
25 V, X7R, 0805) and GRM21BR71A106K (10 mF, 10 V,
X7R, 0805).
No−Load Regulation Considerations
The NCP605/NCP606 adjustable regulator will operate
properly under conditions where the only load current is
through the resistor divider that sets the output voltage.
However, in the case where the NCP605/NCP606 is
configured to provide a 1.250 V output, there is no resistor
divider. If the part is enabled under no−load conditions,
leakage current through the pass transistor at junction
temperatures above 85°C can approach several microamps,
especially as junction temperature approaches 150°C. If this
leakage current is not directed into a load, the output voltage
will rise up to a level approximately 20 mV above nominal.
The NCP605/ NCP606 contains an overshoot clamp
circuit to improve transient response during a load current
step release. When output voltage exceeds the nominal by
approximately 20 mV, this circuit becomes active and
clamps the output from further voltage increase. Tying the
ENABLE pin to V
in
(NCP606 only) will ensure that the part
is active whenever the supply voltage is present, thus
guaranteeing that the clamp circuit is active whenever
leakage current is present.
When the NCP606 adjustable regulator is disabled, the
overshoot clamp circuit becomes inactive and the pass
transistor leakage will charge any capacitance on V
out
. If no
load is present, the output can charge up to within a few
millivolts of V
in
. In most applications, the load will present
some impedance to V
out
such that the output voltage will be
inherently clamped at a safe level. A minimum load of
10 mA is recommended.
Unlike LP8345, for NCP605/606 fixed voltage versions
there is no limitation for minimum load current.
Noise Decoupling
The NCP605/NCP606 is a low noise regulator and needs
no external noise reduction capacitor. Unlike other low noise
regulators which require an external capacitor and have slow
startup times, the NCP605/NCP606 operates without a noise
reduction capacitor, has a typical 8 ms turn−on time and
achieves a 50 mV
rms
overall noise level between 10 Hz and
100 kHz.
Enable Operation (NCP606 Only)
The enable pin will turn the regulator on or off. The
threshold limits are covered in the electrical characteristics
table in this data sheet. The turn−on/turn−off transient
voltage being supplied to the enable pin should exceed a
slew rate of 10 mV/ms to ensure correct operation. If the
enable function is not to be used then the pin should be
connected to V
in
.
Output Voltage Adjust
The output voltage can be adjusted from 1 times (Figure
4) to 4 times (Figure 3) the typical 1.250 V regulation
voltage via the use of resistors between the output and the
ADJ input. The output voltage and resistors are chosen using
Equation 1 and Equation 2.
V
out
+ 1.250
ǒ
1 )
R
1
R
2
Ǔ
)
ǒ
I
ADJ
R
1
Ǔ
(eq. 1)
(eq. 2)
R
2
^
R
1
V
out
1.25
* 1
Input bias current I
ADJ
is typically less than 150 nA.
Choose R
1
arbitrarily to minimize errors due to the bias
current and to minimize noise contribution to the output
voltage. Use Equation 2 to find the required value for R
2
.
Thermal
As power in the NCP605/NCP606 increases, it might
become necessary to provide some thermal relief. The
maximum power dissipation supported by the device is
dependent upon board design and layout. Mounting pad
configuration on the PCB, the board material, and the
ambient temperature affect the rate of junction temperature
rise for the part. When the NCP605/NCP606 has good
thermal conductivity through the PCB, the junction
temperature will be relatively low with high power
applications. The maximum dissipation the
NCP605/NCP606 can handle is given by:
P
D(MAX)
+
ƪ
T
J(MAX)
* T
A
ƫ
R
QJA
(eq. 3)
Since T
J
is not recommended to exceed 125°C (T
J(MAX)
),
then the NCP605/NCP606 soldered on 645 mm
2
, 1 oz
copper area, FR4 can dissipate up to 1.3 W when the ambient
