TM
MP2104 – 1.7MHz 600mA SYNCHRONOUS STEP-DOWN CONVERTER
APPLICATION INFORMATION
Output Voltage Setting (MP2104DJ)
The external resistor divider sets the output
voltage (see Figure 3). The feedback resistor R1
also sets the feedback loop bandwidth with the
internal compensation capacitor (see Figure 1).
Choose R1 around 300kΩ for optimal transient
response. R2 is then given by:
R2
=
R1
V
OUT
−
1
0 .6 V
Inductor Selection
A 1µH to 10µH inductor with DC current rating
at least 25% higher than the maximum load
current is recommended for most applications.
For best efficiency, the inductor DC resistance
shall 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
Table 1—Resistor Selection vs. Output
Voltage Setting
V
OUT
1.2V
1.5V
1.8V
2.5V
R1
300k
Ω
(1%)
300k
Ω
(1%)
300k
Ω
(1%)
300k
Ω
(1%)
R2
300k
Ω
(1%)
200k
Ω
(1%)
150k
Ω
(1%)
95.3k
Ω
(1%)
Where
∆I
L
is the inductor ripple current. Choose
inductor ripple current approximately 30% of the
maximum load current, 600mA.
The maximum inductor peak current is:
I
L(MAX )
=
I
LOAD
+
∆
I
L
2
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
Coilcraft
Toko
Sumida
Taiyo Yuden
Part Number
LP1704-222M
D312C
CDRH3D16
LBC2518
Inductance (µH)
2.2
2.2
2.2
2.2
Max DCR (Ω)
0.07
0.14
0.072
0.13
Saturation
Current (A)
1.7
1.0
1.2
0.6
Dimensions
LxWxH (mm
3
)
6.5x5.3x2
3.6x3.6x1
4x4x1.8
2.5x1.8x1.8
Table 3—Inductors for Improved Efficiency at 25mA, 50mA, under 100mA Load.
Manufacturer
Coilcraft
Murata
Sumida
Sumida
Sumida
Part Number
DO1605T-103MX
LQH4C100K04
CMD4D06-100
CR32-100
CR54-100
Inductance (µH)
10
10
10
10
10
Max DCR (Ω)
0.3
0.2
0.3
0.2
0.1
Saturation
Current (A)
1.0
1.2
0.7
1.0
1.2
I
RMS
(A)
0.9
0.8
0.5
0.7
1.4
MP2104 Rev. 1.3
10/4/2005
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8
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