NCP170
www.onsemi.com
20
APPLICATIONS INFORMATION
General
The NCP170 is a high performance 150 mA Linear
Regulator with Ultra Low IQ. This device delivers low
Noise and high Power Supply Rejection Ratio with excellent
dynamic performance due to employing the Dynamic
Quiescent Current adjustment which assure ultra low IQ
consumption at no – load state. These parameters make this
device very suitable for various battery powered
applications.
Input Decoupling (CIN)
It is recommended to connect at least a 1 mF Ceramic X5R
or X7R capacitor between IN and GND pins of the device.
This capacitor will provide a low impedance path for any
unwanted AC signals or Noise superimposed onto constant
Input Voltage. The good input capacitor will limit the
influence of input trace inductances and source resistance
during sudden load current changes.
Higher capacitance and lower ESR Capacitors will
improve the overall line transient response.
Output Decoupling (COUT)
The NCP170 does not require a minimum Equivalent
Series Resistance (ESR) for the output capacitor. The device
is designed to be stable with standard ceramics capacitors
with values of 1.0 mF or greater up to 10 mF. The X5R and
X7R types have the lowest capacitance variations over
temperature thus they are recommended. There is
recommended connect the output capacitor as close as
possible to the output pin of the regulator.
Enable Operation
The NCP170 uses the EN pin to enable /disable its device
and to activate /deactivate the active discharge function at
devices with this feature. If the EN pin voltage is pulled
below 0.4 V the device is guaranteed to be disable. The
active discharge transistor at the devices with Active
Discharge Feature is activated and the output voltage VOUT
is pulled to GND through an internal circuitry with effective
resistance about 100 ohms.
If the EN pin voltage is higher than 1.2 V the device is
guaranteed to be enabled. The internal active discharge
circuitry is switched off and the desired output voltage is
available at output pin. In case the Enable function is not
required the EN pin should be connected directly to input
pin.
Thermal Shutdown
When the die temperature exceeds the Thermal Shutdown
point (TSD = 175°C typical) the device goes to disabled state
and the output voltage is not delivered until the die
temperature decreases to 150°C. The Thermal Shutdown
feature provides a protection from a catastrophic device
failure at accidental overheating. This protection is not
intended to be used as a substitute for proper heat sinking.
Power Dissipation and Heat sinking
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. For reliable operation, junction temperature
should be limited to +125°C. The maximum power
dissipation the NCP170 device can handle is given by:
PD(MAX) +ƪTJ(MAX) *TAƫ
RqJA
(eq. 1)
The power dissipated by the NCP170 device for given
application conditions can be calculated from the following
equations:
PD[VINǒIGND(IOUT)Ǔ)IOUTǒVIN *VOUTǓ(eq. 2)
or
VIN(MAX) [
PD(MAX) )ǒVOUT IOUTǓ
IOUT )IGND
(eq. 3)
Hints
VIN and GND printed circuit board traces should be as
wide as possible. When the impedance of these traces is
high, there is a chance to pick up noise or cause the regulator
to malfunction. Place external components, especially the
output capacitor, as close as possible to the NCP170, and
make traces as short as possible.