TM
MP2101 – 1.6MHz SYNCHRONOUS STEP-DOWN PLUS 200mA LDO
APPLICATION INFORMATION
Output Voltage Setting
Inductor Selection
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).
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 <200mꢀ. See Table
2
for
R1 of the switcher should be 300kꢀ for optimal
transient response. R2 is then given by:
recommended inductors and manufacturers.
For most designs, the inductance value can be
derived from the following equation:
R1
R2 =
VOUT1
VOUT
×
(
V
− VOUT
)
IN
− 1
L =
0.6V
V × ∆IL × fOSC
IN
R4 of the LDO should be 60kꢀ for good loop
Where ∆IL is inductor ripple current.
response. R3 is then given by:
Choose the inductor ripple current to be
approximately 30% of the maximum load
current (800mA).
VOUT2
R3 = R4× (
−1)
0.6V
The maximum inductor peak current is:
Table 1—Resistor Selection vs. Output
Voltage Setting
∆IL
IL(MAX) = ILOAD
+
2
VOUT
R1
R2
R3
R4
Under light load conditions below 100mA, larger
inductance is recommended for improved
efficiency. Table 3 lists inductors recommended
for this purpose.
60kꢀ
(1%)
60kꢀ
300kꢀ
(1%)
300kꢀ
(1%)
1.2V
(1%)
90kꢀ
(1%)
60kꢀ
300kꢀ
200kꢀ
1.5V
1.8V
2.5V
(1%)
(1%)
(1%)
120kꢀ
(1%)
60kꢀ
300kꢀ
(1%)
150kꢀ
(1%)
(1%)
190kꢀ
(1%)
60kꢀ
300kꢀ
(1%)
95.3kꢀ
(1%)
(1%)
Table 2—Suggested Surface Mount Inductors
Saturation
Current (A)
Dimensions
Manufacturer
Sumida
Part Number
CDRH2D11
D521C
Inductance (µH) Max DCR (Ω)
LxWxH (mm3)
2.2
2.2
2.2
0.098
0.059
0.072
1.27
1.63
1.20
3.2 x 3.2 x 1.2
5 x 5 x 1.5
4 x 4 x 1.8
Toko
Sumida
CDRH3D16
Table 3—Inductors for Improved Efficiency at 25mA, 50mA, under 100mA Load.
Saturation
Manufacturer
Part Number
DO1605T-103MX
LQH4C100K04
CR32-100
Inductance (µH) Max DCR (Ω)
Current (A)
IRMS (A)
Coilcraft
Murata
Sumida
Sumida
10
10
10
10
0.3
0.2
0.2
0.1
1.0
1.2
1.0
1.2
0.9
0.8
0.7
1.4
CR54-100
MP2101 Rev. 1.0
8/18/2006
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