NCP51460 Просмотр технического описания (PDF) - ON Semiconductor
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NCP51460 Datasheet PDF : 12 Pages
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NCP51460
APPLICATIONS INFORMATION
Input Decoupling Capacitor (CIN)
It is recommended to connect a 0.1 mF Ceramic capacitor
between VIN and GND pin of the device. This capacitor will
provide a low impedance path for unwanted AC signals or
noise present on the input voltage. The input capacitor will
also limit the influence of input trace inductances and Power
Supply resistance during sudden load current changes.
Higher capacitances will improve the Power Supply
Rejection Ratio and line transient response.
Output Decoupling Capacitor (COUT)
The NCP51460 was designed to be stable without an
additional output capacitor. Without the output capacitor the
VOUT settling times during Reference Turn−on or Turn−off
can be as short as 20 ms (Refer to Figure 24 and 25). The
Load Transient Responses without COUT (Figure 21 and 22)
show good stability of NCP51460 even for fast output
current changes from 0 mA to full load. If smaller VOUT
deviations during load current changes are required, it is
possible to add some external capacitance as shown on
Figure 26.
VIN = 4.2 to 28 V
CIN
0.1 mF
VIN
VOUT
NCP51460
(3.3 V fixed)
GND
COUT
VOUT
3.3 V
Figure 26. Output Capacitor Connection
The COUT will reduce the overshoot and undershoot but
will increase the settling time and can introduce some
ringing of the output voltage during fast load transients.
NCP51460 behavior for different values of ceramic X7R
output capacitors is depicted on Figure 23.
The Output Voltage ringing and settling times can be
reduced by using some additional resistance in series with
the Ceramic Capacitor or by using Tantalum or Aluminum
Capacitors which have higher ESR values. Figure 27 below
shows the Load Transient improvement after adding an
additional 2 W series resistor to a 1 mF Ceramics Capacitor.
3.35
3.30
3.25
VOUT
COUT = 1 mF MLCC + 2 W
3.35
3.30
3.25
COUT = 1 mF MLCC
IOUT = 10 mA
VIN = 5.8 V, TA = 25°C,
trise_fall = 10 mA/1 ms
IOUT = 0 mA
TIME (50 ms/DIV)
Figure 27.
The device was determined to be stable with Aluminum,
Ceramic and Tantalum Capacitors with capacitances
ranging from 0 to 100 mF at TA = 25°C.
Turn−On Response
It is possible to achieve very fast Turn−On time when fast
VIN ramp is applied to NCP51460 input as shown on
Figure 24. However if the Input Voltage change from 0 V to
nominal Input Voltage is extremely fast, the Output Voltage
settling time will increase. Figure 28 below shows this effect
when the Input Voltage change is 5.8 V / 2 ms.
6
4
2 VIN
0
3
2
1 VOUT
0
VIN = 0 V to 5.8 V,
CIN = 0 mF,
COUT = 0 mF,
IOUT = 0 mA, TA = 25°C,
trise = 45 ms
TIME (10 ms/DIV)
Figure 28.
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