MP1410EP-Z データシートの表示（PDF） - Monolithic Power Systems
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MP1410EP-Z Datasheet PDF : 9 Pages
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Monolithic Power Systems
Application Information (Continued)
The characteristics of the output capacitor also
effect the stability of the regulation control
system. Ceramic, tantalum, or low-ESR
electrolytic capacitors are recommended.
In the case of ceramic capacitors, the
impedance at the switching frequency is
dominated by the capacitance, and so the
output voltage ripple is mostly independent of
the ESR. The output voltage ripple is
estimated to be:
VRIPPLE ~= 1.4 * VIN * (fLC/fSW)^2
Where VRIPPLE is the output ripple voltage, VIN
is the input voltage, fLC is the resonant
frequency of the LC filter, fSW is the switching
frequency.
In the case of tantalum or low-ESR electrolytic
capacitors, the ESR dominates the impedance
at the switching frequency, and so the output
ripple is calculated as:
VRIPPLE ~= ∆I * RESR
Where VRIPPLE is the output voltage ripple, ∆I is the
inductor ripple current, and RESR is the equivalent
series resistance of the output capacitors.
Output Rectifier Diode
The output rectifier diode supplies the current
to the inductor when the high-side switch is off.
To reduce losses due to the diode forward
voltage and recovery times, use a Schottky
rectifier.
Choose a rectifier who’s maximum reverse
voltage rating is greater than the maximum
input voltage, and who’s current rating is
greater than the maximum load current.
Table 1 provides a list of manufacturer’s and
their websites.
MP1410
2A Step-Down
Switch-Mode Regulator
PRELIMINARY
Table 1: Schottky Diode Manufacturers
# Manufacturer
1 Diodes, Inc.
2 Fairchild Semiconductor
3 General Semiconductor
4 International Rectifier
5 On Semiconductor
6 Pan Jit International
Website
www.diodes.com
www.fairchildsemi.com
www.gensemi.com
www.irf.com
www.onsemi.com
www.panjit.com.tw
Compensation
The output of the transconductance error
amplifier is used to compensate the regulation
system. Typically compensation capacitors,
CC sets the dominant pole. The compensation
resistor sets a zero that should have the same
frequency as the pole set by the load
resistance and the output capacitor. If the
output capacitor is not ceramic type, then there
may need to be another capacitor from COMP
to GND (CCA) to compensate for the zero
produced by the output capacitor and its ESR.
One of the critical parameters is the DC loop
gain. This can be determined by the equation:
AVL = (VFB / VOUT) * AEA * ACS * RL
Where AVL is the loop gain, VFB is the feedback
threshold, 1.22V, VOUT is the regulated output
voltage, AEA is the error amplifier voltage gain,
ACS is the current sense gain, and RL is the
load resistance, or VOUT / ILOAD.
Simplifying the equation:
AVL = AEA * ACS * (VFB / ILOAD(MAX)) ~= 1663 /
ILOAD(MAX)
Another critical parameter is the desired
crossover frequency.
MP1410 Rev 1.0_ 05/29/02
www.monolithicpower.com
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