NCP705
www.onsemi.com
17
APPLICATIONS INFORMATION
General
The NCP705 is a high performance 500 mA Low Dropout
Linear Regulator. This device delivers excellent noise and
dynamic performance. Thanks to its adaptive ground current
feature the device consumes only 13 mA of quiescent current
at no−load condition. The regulator features ultra*low
noise o f 1 2 mVRMS, PSRR of 71 dB at 1 kHz and very good
load/line transient performance. Such excellent dynamic
parameters and small package size make the device an ideal
choice for powering the precision analog and noise sensitive
circuitry in portable applications. The LDO achieves this
ultra low noise level output without the need for a noise
bypass capacitor. A logic EN input provides ON/OFF
control of the output voltage. When the EN is low the device
consumes as low as typ. 10 nA from the IN pin. T he device is
fully protected in case of output overload, output short circuit
condition and overheating, assuring a very robust design.
Input Capacitor Selection (CIN)
It is recommended to connect a minimum of 1 mF Ceramic
X5R or X7R capacitor close to the IN pin of the device. This
capacitor will provide a low impedance path for unwanted
AC signals or noise modulated onto constant input voltage.
There is n o r e q uirement for the min. /max. 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. Larger input capacitor
may be necessary if fast and large load transients are
encountered in the application.
Output Decoupling (COUT)
The NCP705 requires an output capacitor connected as
close as possible to the output pin of the regulator. The
minimal capacitor value is 1 mF and X7R or X5R dielectric
due to its low capacitance variations over the specified
temperature range. The NCP705 is designed to remain stable
with minimum effective capacitance of 1 mF to account for
changes with temperature, DC bias and package size.
Especially for small package size capacitors such as 0402
the effective capacitance drops rapidly with the applied DC
bias. Refer to the Figure 64, for the capacitance vs. package
size and DC bias voltage dependence.
There is no requirement for the minimum value of
Equivalent Series Resistance (ESR) for the COUT but the
maximum value of ESR should be less than 900 mW. Larger
output capacitors and lower ESR could improve the load
transient response or high frequency PSRR as shown in
typical characteristics. It is not recommended to use
tantalum c a p a c i t o r s o n t h e output due to their lar ge ESR. The
equivalent series resistance of tantalum capacitors is also
strongly dependent on the temperature, increasing at low
temperature. The tantalum capacitors are generally more
costly than ceramic capacitors.
Figure 64. Capacitance Change vs. DC Bias
1206
0805
0603
0402
DC BIAS (V)
CAPACITY CHANGE (%)
010198762345
10
0
−10
−20
−30
−40
−50
−60
−70
−80
Package Size
No−load Operation
The regulator remains stable and regulates the output
voltage properly within the ±2% tolerance limits even with
no external load applied to the output.
Adjustable Operation
The output voltage range can be set from 0.8 V to
5.5 V−VDO by resistor divider network. Use Equations 1
and 2 to calculate appropriate values of resistors and output
voltage. Typical current to ADJ pin is 1 nA. For output
voltage 0.8 V ADJ pin can be tied directly to Vout pin.
VOUT +0.8 @ǒ1)R1
R2Ǔ)R1@IADJ (eq. 1)
R2^R1@1
VOUT
0.8 *1(eq. 2)
The resistor divider should be designed carefully to
achieve the best performance. Recommended current
through divider is 10 mA and more. Too high values of
resistors (MW) cause increasing noise and longer start−up
time. The suggested values of the resistors are in Table 5. To
improve dynamic performance capacitor C1 should be at
least 1 nF. Recommended range of capacity is between
10 nF and 100 nF. Higher value of capacitor C1 increasing
start−up time.
Table 5. Proposal Resistor Values for Variuos VOUT
VOUT R1 R2
1.5 V 130k 150k
3.3 V 256k 82k
5.0 V 430k 82k