MP1496S – SYNCHRONOUS, STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
APPLICATION INFORMATION
Choose an inductor ripple current to be
approximately 30% of the maximum load
current. The maximum inductor peak current is:
Setting the Output Voltage
The external resistor divider sets the output
voltage (see the Typical Application on page 1).
The feedback resistor R1 sets the feedback
loop bandwidth. R2 is then given by:
IL
IL(MAX) ILOAD
2
Use a larger inductance for improved light-load
efficiency.
R1
R2
VOUT
1
Selecting the Input Capacitor
The input current to the step-down converter is
0.807V
discontinuous, and therefore requires
a
The T-type network shown in Figure 4 is highly
recommended.
capacitor to supply the AC current to the step-
down converter while maintaining the DC-input
voltage. Use low-ESR capacitors for best
performance, especially ceramic capacitors with
X5R or X7R dielectrics for their low ESR and
small temperature coefficients. For most
applications, use a 22µF capacitor.
R1
RT
8
FB
VOUT
R2
Figure 4: T-Type Network
Since the input capacitor (C1) absorbs the input
switching current, it requires an adequate ripple
current rating. Estimate the RMS current in the
input capacitor with:
Table 1 lists the recommended T-type resistor
values for common output voltages.
Table 1: Resistor Selection for Common Output
Voltages
VOUT
VIN
VOUT
VIN
V
OUT (V)
1.0
1.2
1.8
2.5
3.3
5
R1 (kΩ)
20.5
R2 (kΩ)
82
Rt (kΩ)
82
IC1 ILOAD
1
30.1
60.4
32.4
19.1
13
82
The worse case condition occurs at VIN = 2VOUT
,
where:
40.2
56
40.2
33
ILOAD
IC1
40.2
33
2
40.2
7.68
33
For simplification, choose an input capacitor
with an RMS current rating greater than half the
maximum load current.
Selecting the Inductor
Use a 1µH-to-10µH inductor with a DC current
rating of at least 25% percent higher than the
maximum load current for most applications.
Select an inductor with a DC resistance less
than 15mꢀ for highest efficiency. For most
designs, the inductance value can be derived
from the following equation.
The input capacitor can be electrolytic, tantalum
or ceramic. When using electrolytic or tantalum
capacitors, place a small, high quality ceramic
capacitor—e.g. 0.1μF—as close to the IC as
possible. When using ceramic capacitors, make
sure that they have enough capacitance to
provide sufficient charge to prevent excessive
voltage ripple at input. The input voltage ripple
caused by capacitance can be estimated by:
VOUT (V VOUT
)
IN
L1
V IL fOSC
IN
ILOAD
VOUT
VOUT
Where ∆IL is the inductor ripple current.
V
1
IN
fS C1
V
IN
V
IN
MP1496S Rev.1.1
3/29/2017
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