ncp1523b ON Semiconductor, ncp1523b Datasheet - Page 14

• Manufacturer Part Number: ncp1523b
• Description: 3 Mhz, 600 Ma, Highefficiency, Adjustable Output Voltage Stepdown Converter
• Manufacturer: ON Semiconductor

Output Voltage Selection
resistor divider connected from ADJ to FB then to GND. For
low power consumption and noise immunity, the resistor
from FB to GND (R2) should be in the [100 kW − 600 kW]
range. If R2 is 200 kW given the V
through the divider will be 3 mA.
desired R1 and the R1 value,
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•
•
•
Input Capacitor Selection
with large switching noise. Using an input bypass capacitor
can reduce the peak current transients drawn from the input
supply
significantly. The capacitance needed for the input bypass
capacitor depends on the source impedance of the input
supply.
with maximum output current, which is IO, max/2.
should be used for most of the cases. For effective bypass
results, the input capacitor should be placed as close as
possible to the V
Output L−C Filter Design Considerations:
voltage mode architecture. The correct selection of the
output filter ensures good stability and fast transient
response.
filter must be selected to work with internal compensation.
For NCP1523, the internal compensation is internally fixed
and it is optimized for an output filter of L = 2.2 mH and
C
f c +
Table 1. LIST OF INPUT CAPACITOR
OUT
The output voltage is programmed through an external
The formula below gives the value of V
In PWM operating mode, the input current is pulsating
The maximum RMS current occurs at 50% duty cycle
For NCP1523, a low profile ceramic capacitor of 4.7 mF
The NCP1523 is built in 3 MHz frequency and uses
Due to the nature of the buck converter, the output L−C
The corner frequency is given by:
V
V
R1: feedback resistor from V
R2: feedback resistor from FB to GND
OUT
FB
2 p L
Taiyo Yuden
= 4.7 mF
: feedback voltage = 0.6 V
Murata
: output voltage (volts)
TDK
source,
1
C OUT
V OUT + V FB
IN
thereby
Pin.
+
2 p 2.2 mH
GRM188R60J475KE
GRM21BR71C475KA
JMK212BY475MG
C2012X5R0J475KT
C1608X5R0J475KT
reducing
OUT
1
1 ) R1
FB
to FB
is 0.6 V, the current
R2
4.7 mF
switching
OUT
APPLICATION INFORMATION
+ 49.5 KHz
, given the
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noise
NCP1523
14
and maximum of 4.7 mH.
check the loop stability depending of the output ripple
voltage accepted and output current required. For lower
frequency, the stability will be increase; a larger output
capacitor value could be chosen without critical effect on the
system. On the other hand, a smaller capacitor value
increases the corner frequency and it should be critical for
the system stability. Take care to check the loop stability.
The phase margin is usually higher than 45°.
Inductor Selection
performances are saturation current and DC resistance and
inductance value. The inductor ripple current (DI
decreases with higher inductance:
DI
L = inductor value
f
higher than the maximum load current plus half the ripple
current:
I
I
efficiency of the converter. For best performances, the DC
resistance should be less than 0.3 W for good efficiency.
SW
L(MAX)
O(MAX)
Table 2. L−C FILTER EXAMPLE
Table 3. LIST OF INDUCTOR
The device operates with inductance value between 1 mH
If the corner frequency is moved, it is recommended to
The inductor parameters directly related to device
The Saturation current of the inductor should be rated
The inductor’s resistance will factor into the overall
L
Inductance (L)
= peak to peak inductor ripple current
= Switching frequency
Taiyo Yuden
Coil Craft
2.2 mH
4.7 mH
1 mH
Maximum inductor current
FDK
TDK
Maximum Output current
DI L +
I L(MAX) + I O(MAX) )
L
V OUT
MIPW3226 Series
VLF3010AT Series
TFC252005 Series
LQ CBL2012
DO1605−T Series
LPO3010
f SW
Output Capacitor (C
1−
V OUT
V IN
4.7 mF
2.2 mF
10 mF
DI L
2
OUT
)
L
)