MP1583 查看數據表（PDF） - Unspecified
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MP1583 Datasheet PDF : 11 Pages
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Monolithic Power Systems
The system has one zero of importance, due
to the compensation capacitor (C3) and the
compensation resistor (R3). The zero is:
fZ1 = 1 / (2π*R3*C3)
If large value capacitors with relatively high
equivalent-series-resistance (ESR) are used,
the zero due to the capacitance and ESR of
the output capacitor can be compensated by a
third pole set by R3 and C6. The pole is:
fP3 = 1 / (2π*R3*C6)
The system crossover frequency (the
frequency where the loop gain drops to 1, or
0dB) is important. A good rule of thumb is to
set the crossover frequency to approximately
1/5 of the switching frequency. In this case,
the switching frequency is 385KHz, so use a
crossover frequency, fC, of 40KHz. Lower
crossover frequencies result in slower
response and worse transient load recovery.
Higher crossover frequencies can result in
instability.
Table 5: Compensation Values for Typical
Output Voltage/Capacitor Combinations
VOUT
2.5V
3.3V
5V
12V
2.5V
3.3V
5V
12V
2.5V
3.3V
5V
12V
C5
22µF Ceramic
22µF Ceramic
22µF Ceramic
22µF Ceramic
47µF SP-Cap
47µF SP-Cap
47µF SP-Cap
47µF SP-Cap
560µF/6.3V
(30mΩ ESR)
560µF/6.3V
(30mΩ ESR)
470µF/10V
(30mΩ ESR)
220µF/25V
(30mΩ ESR)
R3
3.9KΩ
4.7KΩ
7.5KΩ
10KΩ
8.2KΩ
10KΩ
10KΩ
10KΩ
10KΩ
C3 C4
3.9nF
3.3nF
2.2nF
2.7nF
1.8nF
1.8nF
2.7nF
5.6nF
None
None
None
None
None
None
None
None
15nF 1.5nF
10KΩ 18nF 1.5nF
10KΩ 27nF None
10KΩ 27nF None
MP1583
3A, 23V
Step Down Converter
Choosing the Compensation Components
The values of the compensation components
given in Table 5 yield a stable control loop for
the output voltage and capacitor given. To
optimize the compensation components for
conditions not listed in Table 5, use the
following procedure:
Choose the compensation resistor to set the
desired crossover frequency (See Figure 3).
Determine the value by the following equation:
R3 = 2π*COUT*VOUT*fC / (GEA*GCS*VFB)
Putting in the know constants and setting the
crossover frequency to the desired 40kHz:
R3 ≈ 6.8x107COUT*VOUT
The value of R3 is limited to 10KΩ to prevent
output overshoot at startup, so if the value
calculated for R3 is greater than 10KΩ, use
10KΩ. In this case, the actual crossover
frequency is less than the desired 40kHz, and
is calculated by:
fC = R3*GEA*GCS*VFB / (2π*COUT*VOUT)
or
fC ≈ 5.9 / COUT*VOUT
Choose the compensation capacitor to set the
zero to ¼ of the crossover frequency.
Determine the value by the following equation:
C3 = 2 / π*R3*fC ≈ 1.59x10-5 / R3
if R3 is less than 10KΩ, or if R3 = 10KΩ use
the following equation:
C3 = 4COUT*VOUT / (R32*GEA*GCS*VFB)
C3 ≈ 1.08x10-5 COUT VOUT
MP1583 Rev 2.0_06/30/04
www.monolithicpower.com
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