NCP167
www.onsemi.com
7
APPLICATIONS INFORMATION
General
The NCP167 is an ultra−low noise 700 mA low dropout
regulator designed to meet the requirements of RF
applications and high performance analog circuits. The
NCP167 device provides very high PSRR and excellent
dynamic response. In connection with low quiescent current
this device is well suitable for battery powered application
such as cell phones, tablets and other. The NCP167 is fully
protected in case of current overload, output short circuit and
overheating.
Input Capacitor Selection (C
IN
)
Input capacitor connected as close as possible is necessary
for ensure device stability. The X7R or X5R capacitor
should be used for reliable performance over temperature
range. The value of the input capacitor should be 1 mF or
greater to ensure the best dynamic performance. This
capacitor will provide a low impedance path for unwanted
AC signals or noise modulated onto constant input voltage.
There is no requirement for the ESR of the input capacitor
but it is recommended to use ceramic capacitors for their low
ESR and ESL. A good input capacitor will limit the
influence of input trace inductance and source resistance
during sudden load current changes.
Output Decoupling (C
OUT
)
The NCP167 requires an output capacitor connected as
close as possible to the output pin of the regulator. The
recommended capacitor value is 1 mF and X7R or X5R
dielectric due to its low capacitance variations over the
specified temperature range. The NCP167 is designed to
remain stable with minimum effective capacitance of 0.7 m F
to account for changes with temperature, DC bias and
package size. Especially for small package size capacitors
such as 0201 the effective capacitance drops rapidly with the
applied DC bias. Please refer Figure 21.
Figure 21. Capacity vs DC Bias Voltage
There is no requirement for the minimum value of
Equivalent Series Resistance (ESR) for the C
OUT
but the
maximum value of ESR should be less than 1.7 W. Larger
output capacitors and lower ESR could improve the load
transient response or high frequency PSRR. It is not
recommended to use tantalum capacitors on the output due
to their large ESR. The equivalent series resistance of
tantalum capacitors is also strongly dependent on the
temperature, increasing at low temperature.
Enable Operation
The NCP167 uses the EN pin to enable/disable its device
and to deactivate/activate the active discharge function. If
the EN pin voltage is <0.4 V the device is guaranteed to be
disabled. The pass transistor is turned−off so that there is
virtually no current flow between the IN and OUT. The
active discharge transistor is active so that the output voltage
V
OUT
is pulled to GND through a 280 W resistor. In the
disable state the device consumes as low as typ. 10 nA from
the V
IN
. If the EN pin voltage >1.2 V the device is
guaranteed to be enabled. The NCP167 regulates the output
voltage and the active discharge transistor is turned−off. The
EN pin has internal pull−down current source with typ. value
of 200 nA which assures that the device is turned−off when
the EN pin is not connected. In the case where the EN
function isn’t required the EN should be tied directly to IN.
Output Current Limit
Output Current is internally limited within the IC to a
typical 1000 mA. The NCP167 will source this amount of
current measured with a voltage drops on the 90% of the
nominal V
OUT
. If the Output Voltage is directly shorted to
ground (V
OUT
= 0 V), the short circuit protection will limit
the output current to 1050 mA (typ.). The current limit and
short circuit protection will work properly over whole
temperature range and also input voltage range. There is no
limitation for the short circuit duration.
Thermal Shutdown
When the die temperature exceeds the Thermal Shutdown
threshold (T
SD
= 160°C typical), Thermal Shutdown event
is detected and the device is disabled. The IC will remain in
this state until the die temperature decreases below the
Thermal Shutdown Reset threshold (T
SDU
= 140°C typical).
Once the IC temperature falls below the 140°C the LDO is
enabled again. The thermal shutdown feature provides the
protection from a catastrophic device failure due to
accidental overheating. This protection is not intended to be
used as a substitute for proper heat sinking.
Reverse Current
The PMOS pass transistor has an inherent body diode
which will be forward biased in the case that V
OUT
> V
IN
.
Due to this fact in cases, where the extended reverse current
condition can be anticipated the device may require
additional external protection.
