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MP1430 Datasheet PDF : 11 Pages
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MP1430 – 3A, 28V, 385KHz STEP-DOWN CONVERTER
Table 3—Compensation Values for Typical
Output Voltage/Capacitor Combinations
VOUT
1.8V
2.5V
3.3V
5V
12V
1.8
2.5V
3.3V
5V
2.5V
3.3V
5V
12V
L
4.7µH
4.7-
6.8µH
6.8-
10µH
10-
15µH
15-
22µH
4.7µH
4.7-
6.8µH
6.8-
10µH
10-
15µH
4.7-
6.8µH
6.8-
10µH
10-
15µH
15-
22µH
CO
100µF
Ceramic
47µF
Ceramic
22µFx2
Ceramic
22µFx2
Ceramic
22µFx2
Ceramic
100µF
SP-CAP
47µF
SP-CAP
47µF
SP-CAP
47µF
SP CAP
560µF Al.
30mΩ ESR
560µF Al
30mΩ ESR
470µF Al.
30mΩ ESR
220µF Al.
30mΩ ESR
R3 C3 C6
5.6kΩ 3.3nF None
3.9kΩ 5.6nF None
5.6kΩ 8.2nF None
7.5kΩ 10nF None
10kΩ 3.3nF None
5.6kΩ 3.3nF 100pF
4.7kΩ 5.6nF None
6.8kΩ 10nF None
10kΩ 10nF None
10kΩ 5.6nF 1.5nF
10kΩ 8.2nF 1.5nF
15kΩ 5.6nF 1nF
15kΩ 4.7nF 390pF
To optimize the compensation components for
conditions not listed in Table 3, the following
procedure can be used.
1. Choose the compensation resistor (R3) to set
the desired crossover frequency. Determine the
R3 value by the following equation:
R3 = 2π × CO × fC × VOUT
GEA × GCS
VFB
Where fC is the desired crossover frequency
(which typically has a value no higher than
38KHz).
2. Choose the compensation capacitor (C3) to
achieve the desired phase margin. For
applications with typical inductor values, setting
the compensation zero, fZ1, below one forth of
the crossover frequency provides sufficient
phase margin.
Determine the C3 value by the following equation:
C3 >
4
2π × R3 × fC
Where, R3 is the compensation resistor value and
fC is the desired crossover frequency, 38KHz.
3. Determine if the second compensation
capacitor (C6) is required. It is required if the ESR
zero of the output capacitor is located at less than
half of the 385KHz switching frequency, or the
following relationship is valid:
1
< fS
2π × CO × RESR 2
Where, CO is the output capacitance value, RESR
is the ESR value of the output capacitor, and fS is
the 385KHz switching frequency. If this is the
case, then add the second compensation
capacitor (C6) to set the pole fP3 at the location of
the ESR zero. Determine the C6 value by the
equation:
C6 = CO × RESR
R3
Where, CO is the output capacitance value, RESR
is the ESR value of the output capacitor, and R3
is the compensation resistor.
External Bootstrap Diode
It is recommended that an external bootstrap
diode be added when the system has a 5V fixed
input or the power supply generates a 5V output.
This helps improve the efficiency of the regulator.
The bootstrap diode can be a low cost one such
as IN4148 or BAT54.
5V
1
BS
MP1430
3
SW
10nF
MP1430_F02
Figure 2—External Bootstrap Diode
This diode is also recommended for high duty
cycle operation (when VOUT >65%) and high
VIN
output voltage (VOUT>12V) applications.
MP1430 Rev. 1.0
11/1/2005
www.MonolithicPower.com
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