MP2160 – 1.2A PEAK, 6V, 3.5MHz SYNCHRONOUS STEP-DOWN SWITCHER
MP2160 Rev. 1.03 www.MonolihicPower.com 10
7/5/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
APPLICATION INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
The external resistor divider is used to set the
output voltage (see Typical Application on page
1). The feedback resistor R1 can not be too
large neither too small considering the trade-off
for stability and dynamic. Choose R1 to be
around 40k to 80k. R2 is then given by:
out
R1
R2
V
1
0.6
The feedback circuit is shown as Figure 2.
R1
R2
Vout
FB
MP2160
Figure 2: Feedback Network
Table 1 lists the recommended resistors value
for common output voltages.
Table 1—Resistor Selection for Common
Output Voltages
V
OUT
(V) R1 (kΩ) R2 (kΩ)
1.0 40(1%) 60(1%)
1.2 40(1%) 40(1%)
1.8 60(1%) 30(1%)
2.5 80(1%) 25(1%)
3.3 80(1%) 17.7(1%)
Selecting the Inductor
A 0.15µH to 1µH inductor is recommended for
most applications. For highest efficiency, the
inductor DC resistance should be less than
15m. For most designs, the inductance value
can be derived from the following equation.
OUT IN OUT
1
IN L OSC
V(VV)
L
VIf
Where I
L
is the inductor ripple current.
Choose inductor current to be approximately
30% of the maximum load current. The
maximum inductor peak current is:
2
I
II
L
LOAD)MAX(L
Selecting the Input Capacitor
The input current to the step-down converter is
discontinuous, therefore a capacitor is required
to supply the AC current to the step-down
converter while maintaining the DC input
voltage. Use low ESR capacitors for the best
performance. Ceramic capacitors with X5R or
X7R dielectrics are highly recommended
because of their low ESR and small
temperature coefficients. For most applications,
a 10µF capacitor is sufficient. For higher output
voltage, 22F may be needed for more stable
system.
Since the input capacitor absorbs the input
switching current it requires an adequate ripple
current rating. The RMS current in the input
capacitor can be estimated by:
IN
OUT
IN
OUT
LOAD1C
V
V
1
V
V
II
The worse case condition occurs at V
IN
= 2V
OUT
,
where:
2
I
I
LOAD
1C
For simplification, choose the input capacitor
whose RMS current rating greater than half of
the maximum load current.
The input capacitor can be electrolytic, tantalum
or ceramic. When using electrolytic or tantalum
capacitors, a small and high quality ceramic
capacitor, i.e. 0.1F, should be placed 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:
LOAD OUT OUT
IN
IN
SIN
IV V
V1
fC1V V
