TM
MP2101 – 1.6MHz SYNCHRONOUS STEP-DOWN PLUS 200mA LDO
APPLICATION INFORMATION
Output Voltage Setting
The external resistor divider sets the output
voltage. The feedback resistor R1 of the switcher
also sets the feedback loop bandwidth with the
internal compensation capacitor (see Figure 1).
R1 of the switcher should be 300kΩ for optimal
transient response. R2 is then given by:
R2
=
R1
V
OUT1
−
1
0 .6 V
Inductor Selection
A 1µH to 10µH inductor with a DC current rating
of at least 25% higher than the maximum load
current is recommended for most applications.
For best efficiency, the inductor DC resistance
should be <200mΩ. See Table 2 for
recommended inductors and manufacturers.
For most designs, the inductance value can be
derived from the following equation:
L
=
V
OUT
×
(
V
IN
−
V
OUT
)
V
IN
× ∆
I
L
×
f
OSC
R4 of the LDO should be 60kΩ for good loop
response. R3 is then given by:
R3
=
R4
×
(
V
OUT2
−
1)
0. 6 V
Table 1—Resistor Selection vs. Output
Voltage Setting
V
OUT
R1
300k
Ω
(1%)
300k
Ω
(1%)
300k
Ω
(1%)
300k
Ω
(1%)
Where
∆I
L
is inductor ripple current.
Choose the inductor ripple current to be
approximately 30% of the maximum load
current (800mA).
The maximum inductor peak current is:
I
L(MAX )
=
I
LOAD
+
∆
I
L
2
R2
300k
Ω
(1%)
200k
Ω
(1%)
150k
Ω
(1%)
95.3k
Ω
(1%)
R3
R4
1.2V
1.5V
1.8V
2.5V
60kΩ
(1%)
90kΩ
(1%)
120kΩ
(1%)
190kΩ
(1%)
60kΩ
(1%)
60kΩ
(1%)
60kΩ
(1%)
60kΩ
(1%)
Under light load conditions below 100mA, larger
inductance is recommended for improved
efficiency. Table 3 lists inductors recommended
for this purpose.
Table 2—Suggested Surface Mount Inductors
Manufacturer
Sumida
Toko
Sumida
Part Number
CDRH2D11
D521C
CDRH3D16
Inductance (µH)
2.2
2.2
2.2
Max DCR (Ω)
0.098
0.059
0.072
Saturation
Current (A)
1.27
1.63
1.20
Dimensions
LxWxH (mm
3
)
3.2 x 3.2 x 1.2
5 x 5 x 1.5
4 x 4 x 1.8
Table 3—Inductors for Improved Efficiency at 25mA, 50mA, under 100mA Load.
Manufacturer
Coilcraft
Murata
Sumida
Sumida
Part Number
DO1605T-103MX
LQH4C100K04
CR32-100
CR54-100
Inductance (µH)
10
10
10
10
Max DCR (Ω)
0.3
0.2
0.2
0.1
Saturation
Current (A)
1.0
1.2
1.0
1.2
I
RMS
(A)
0.9
0.8
0.7
1.4
MP2101 Rev. 1.0
8/18/2006
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9
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