TM
MP1580 – 2A, 380KHz STEP-DOWN CONVERTER
Determine if the second compensation
capacitor, C6, is required. It is required if the
ESR zero of the output capacitor happens at
less than four times the crossover frequency.
Or:
8
π ×
C2
×
R
ESR
×
f
C
≥
1
Negative Output Voltage
The MP1580 can be configured as a buck-
boost regulator to supply negative output
voltage.
Because the GND pin of the IC is now
connected to the negative output voltage, the
maximum allowable input voltage is the IC input
voltage rating (25V) minus the negative output
voltage value. A typical application circuit is
shown in Figure 3.
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
or
7.34
×
10
−
5
×
R3
×
R
ESR
≥
1
V
OUT
If this is the case, add the second
compensation capacitor. Determine the value
by the equation:
C6
=
C2
×
R
ESR(MAX )
R3
Where R
ESR(MAX)
is the maximum ESR of the
output capacitor.
For example:
V
OUT
= 3.3V
C2= 22µF Ceramic (ESR = 10mΩ)
R3
≈
(1.37
×
10
8
)
×
(22
×
10
−
6
)
×
(3.3)
=
9.9k
Ω
BS
MP1580
SW
10nF
MP1580_F02
Use the nearest standard value of 10kΩ.
C3
>
0.22
×
(22
×
10
−
6
)
×
3.3
10
×
10
3
=
1.6nF
Figure 2—External Bootstrap Diode
This diode is also recommended for high duty
cycle operation (when
V
OUT
>65%) and high
V
IN
Use a standard value of 2nF
2
π ×
C2
×
R
ESR
×
f
C
=
0.014
output voltage (V
OUT
>12V) applications.
which is less than 1, therefore no second
compensation capacitor is required.
Table 5—Recommended Components for
Standard Output Voltages
V
OUT
R1
L1 Minimum
1.22V
1.5V
1.8V
2.5V
3.3V
5.0V
0Ω
2.32kΩ
4.75kΩ
10.5kΩ
16.9kΩ
30.9kΩ
6.8µH
6.8µH
10µH
10µH
15µH
22µH
MP1580 Rev. 3.0
12/5/2005
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8
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