NCP186
www.onsemi.com
11
APPLICATIONS INFORMATION
General
The NCP186 is a high performance 1 A low dropout linear
regulator (LDO) delivering excellent noise and dynamic
performance. Thanks to its adaptive ground current
behavior the device consumes only 90 mA typ. of quiescent
current (no−load condition).
The regulator features low noise of 48 mV
RMS
, PSRR of
75 dB at 1 kHz and very good line/load transient
performance. Such excellent dynamic parameters, small
dropout voltage and small package size make the device an
ideal choice for powering the precision noise sensitive
circuitry in portable applications.
A logic EN input provides ON/OFF control of the output
voltage. When the EN is low the device consumes as low as
100 nA typ. from the IN pin.
The device is fully protected in case of output overload,
output short circuit condition or overheating, assuring a very
robust design.
Input Capacitor Selection (C
IN
)
Input capacitor connected as close as possible is necessary
to 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 for
the best dynamic performance. This capacitor will provide
a low impedance path for unwanted AC signals or noise
modulated onto the input voltage.
There is no requirement for the ESR of the input capacitor
but it is recommended to use ceramic capacitor for its low
ESR and ESL. A good input capacitor will limit the
influence of input trace inductance and source resistance
during load current changes.
Output Capacitor Selection (C
OUT
)
The LDO requires an output capacitor connected as close
as possible to the output and ground pins. The recommended
capacitor value is 1 mF, ceramic X7R or X5R type due to its
low capacitance variations over the specified temperature
range. The LDO is designed to remain stable with minimum
effective capacitance of 0.8 mF. When selecting the capacitor
the changes with temperature, DC bias and package size
needs to be taken into account. Especially for small package
size capacitors such as 0201 the effective capacitance drops
rapidly with the applied DC bias voltage (refer the
capacitor’s datasheet for details).
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 0.5 W. Larger
capacitance and lower ESR improves the load transient
response and high frequency PSRR. Only ceramic
capacitors are recommended, the other types like tantalum
capacitors not due to their large ESR.
Enable Operation
The LDO uses the EN pin to enable/disable its operation
and to deactivate/activate the output discharge function
(A−version only).
If the EN pin voltage is < 0.4 V the device is disabled and
the pass transistor is turned off so there is no current flow
between the IN and OUT pins. On A−version the active
discharge transistor is active so the output voltage is pulled
to GND through 34 W (typ.) resistor.
If the EN pin voltage is > 1.0 V the device is enabled and
regulates the output voltage. The active discharge transistor
is turned off.
The EN pin has internal pull−down current source with
value of 150 nA typ. which assures the device is turned off
when the EN pin is unconnected. In case when the EN
function isn’t required the EN pin should be tied directly to
IN pin.
Output Current Limit
Output current is internally limited to a 1.4 A typ. The
LDO will source this current when the output voltage drops
down from the nominal output voltage (test condition is
V
OUT−NOM
– 100mV). If the output voltage is shorted to
ground, the short circuit protection will limit the output
current to 1.4 A typ. The current limit and short circuit
protection will work properly over the whole temperature
and input voltage ranges. There is no limitation for the short
circuit duration.
Thermal Shutdown
When the LDO’s die temperature exceeds the thermal
shutdown threshold value the device is internally disabled.
The IC will remain in this state until the die temperature
decreases by value called thermal shutdown hysteresis.
Once the IC temperature falls this way the LDO is back
enabled. The thermal shutdown feature provides the
protection against overheating due to some application
failure and it is not intended to be used as a normal working
function.
Power Dissipation
Power dissipation caused by voltage drop across the LDO
and by the output current flowing through the device needs
to be dissipated out from the chip. The maximum power
dissipation is dependent on the PCB layout, number of used
Cu layers, Cu layers thickness and the ambient temperature.
The maximum power dissipation can be computed by
following equation:
P
D(MAX)
+
T
J
* T
A
q
JA
[W]
(eq. 1)
Where (T
J
−
T
A
) is the temperature difference between the
junction and ambient temperatures and θ
JA
is the thermal
resistance (dependent on the PCB as mentioned above).
