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:
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.
8π × C2× RESR × fC ≥ 1
or
7.34 ×10−5 × R3 × RESR
≥ 1
VOUT
External Bootstrap Diode
If this is the case, add the second
compensation capacitor. Determine the value
by the equation:
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.
C2 × RESR(MAX)
C6 =
R3
Where RESR(MAX) is the maximum ESR of the
output capacitor.
5V
For example:
BS
VOUT = 3.3V
10nF
MP1580
C2= 22µF Ceramic (ESR = 10mꢀ)
SW
R3 ≈ (1.37 ×108 )× (22 ×10−6 )× (3.3) = 9.9kΩ
Use the nearest standard value of 10kꢀ.
0.22 × (22 ×10−6 )× 3.3
10 ×103
Use a standard value of 2nF
2π × C2× RESR × fC = 0.014
MP1580_F02
Figure 2—External Bootstrap Diode
This diode is also recommended for high duty
VOUT
C3 >
= 1.6nF
cycle operation (when
>65%) and high
VIN
output voltage (VOUT>12V) applications.
which is less than 1, therefore no second
compensation capacitor is required.
Table 5—Recommended Components for
Standard Output Voltages
VOUT
1.22V
1.5V
1.8V
2.5V
3.3V
5.0V
R1
L1 Minimum
6.8µH
0ꢀ
2.32kꢀ
4.75kꢀ
10.5kꢀ
16.9kꢀ
30.9kꢀ
6.8µH
10µH
10µH
15µH
22µH
MP1580 Rev. 3.0
12/5/2005
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