NCP1597AMNTWG ONSEMI [ON Semiconductor], NCP1597AMNTWG Datasheet - Page 11

• Manufacturer Part Number: NCP1597AMNTWG
• Description: 1 MHz, 2.0 A Synchronous Buck Regulator
• Manufacturer: ONSEMI [ON Semiconductor]

Programming the Output Voltage
from the output voltage to FB pin (see Figure 25). So the
output voltage is calculated according to Eq.1.
Inductor Selection
regulator. The selection of inductor involves trade−offs
among size, cost and efficiency. The inductor value is
selected according to the equation 2.
Where V
f − switching frequency, 1.0 MHz;
I
current;
V
maintain a maximum ripple current within 30% of the
maximum load current. If the ripple current exceeds this
30% limit, the next larger value should be selected.
the maximum load current and its saturation current should
be about 30% higher. For robust operation in fault conditions
(start−up or short circuit), the saturation current should be
high enough. To keep the efficiency high, the series
resistance (DCR) should be less than 0.1 W, and the core
material should be intended for high frequency applications.
Output Capacitor Selection
and also provides energy storage. So the major parameter
necessary to define the output capacitor is the maximum
allowed output voltage ripple of the converter. This ripple is
related to capacitance and the ESR. The minimum
capacitance required for a certain output ripple can be
calculated by Equation 4.
ripple
in(max)
The output voltage is set using a resistive voltage divider
The inductor is the key component in the switching
Choose a standard value close to the calculated value to
The inductor’s RMS current rating must be greater than
The output capacitor acts to smooth the dc output voltage
− Ripple current, usually it’s 20% − 30% of output
− maximum input voltage.
out
− the output voltage;
L +
Figure 25. Output divider
V
f @ I
out
V
V
out
ripple
+ V
out
R1
R2
FB
@ 1 *
@
R
1
R
) R
V
FB
2
V
in(max)
out
2
APPLICATION INFORMATION
(eq. 1)
(eq. 2)
http://onsemi.com
11
Where V
calculated by equation 5.
ESR according to Equation 3. If ESR exceeds the value from
Eq.4, multiple capacitors should be used in parallel.
In addition, both surface mount tantalum and through−hole
aluminum electrolytic capacitors can be used as well.
Maximum Output Capacitor
overcurrent limit. It limits the maximum allowed output
capacitor to startup successfully. The maximum allowed
output capacitor can be determined by the equation:
Where T
D
example, with 3.3 V/2.0 A output and 20% ripple, the max
allowed output capacitors is 546 mF.
Input Capacitor Selection
The input capacitor can be calculated by Equation 6.
Where V
Power Dissipation
6−pin, DFN package. When the die temperature reaches
+185°C,
Thermal−Overload Protection section). The power
dissipated in the device is the sum of the power dissipated
from supply current (PQ), power dissipated due to switching
the internal power MOSFET (P
dissipated due to the RMS current through the internal
power MOSFET (PON). The total power dissipated in the
package must be limited so the junction temperature does
not exceed its absolute maximum rating of +150°C at
iPP
The required ESR for this amount of ripple can be
Based on Equation 2 to choose capacitor and check its
Ceramic capacitor can be used in most of the applications.
NCP1597A family has internal 1 ms fixed soft−start and
This is assuming that a constant load is connected. For
The NCP1597A is available in a thermally enhanced
D
max
is the current ripple.
ripple
in(ripple)
+
SS(min)
C
C
in(min)
the
V
out(max)
V
in(min)
is the allowed output voltage ripple.
out
is the minimum soft−start period (1ms);
C
is the required input ripple voltage.
+ I
NCP1597A
OUT(min)
is the maximum duty cycle.
+
out(max)
ESR +
I
lim(min)
+
@ D
8 @ f @ V
V
V
I
* I
ripple
out
ripple
max
shuts
I
load(max)
ripple
T
@
SW
SS(min)
f @ V
ripple
), and the power
down
in(ripple)
1
*
Di
p−p
2
(see
(eq. 3)
(eq. 4)
(eq. 5)
(eq. 6)
(eq. 7)
the