MP2112 查看數據表（PDF） - Monolithic Power Systems
零件编号
产品描述 (功能)
生产厂家
MP2112 Datasheet PDF : 8 Pages
| |||
TM
MP2112 – 1MHz, 1A SYNCHRONOUS STEP-DOWN CONVERTER
Current Mode PWM Control
Slope compensated current mode PWM control
provides stable switching and cycle-by-cycle
current limit for superior load and line response.
This protects the internal main switch and
synchronous rectifier. The MP2112 switches at a
constant frequency (1MHz) and regulates the
output voltage. During each cycle the PWM
comparator modulates the power transferred to the
load by changing the inductor peak current based
on the feedback error voltage. During normal
operation, the main switch is turned on for a certain
time to ramp the inductor current at each rising
edge of the internal oscillator, then switched off
when the peak inductor current rises above the
error voltage. When the main switch is off, the
synchronous rectifier will turn on immediately and
stay on until the next cycle starts.
Dropout Operation
The MP2112 allows the main switch to remain on
for more than one switching cycle and increases
the duty cycle while the input voltage is dropping
close to the output voltage. When the duty cycle
reaches 100%, the main switch continuously
delivers current to the output up to the PFET
current limit. The output voltage is the input
voltage minus the voltage drop across the main
switch and the inductor.
Short Circuit Protection
The MP2112 has short circuit protection. When
the output is shorted to ground, the oscillator
frequency is reduced to prevent the inductor
current from increasing beyond the PFET current
limit. The PFET current limit is also reduced to
lower the short circuit current. The frequency and
current limit will return to the normal values once
the short circuit condition is removed and the
feedback voltage reaches 0.6V.
Maximum Load Current
The MP2112 can operate down to a 2.5V input
voltage; however the maximum load current
decreases at lower input due to a large IR drop on
the main switch and synchronous rectifier. The
slope compensation signal reduces the peak
inductor current as a function of the duty cycle to
prevent sub-harmonic oscillations at duty cycles
greater than 50%. Conversely the current limit
increases as the duty cycle decreases.
APPLICATION INFORMATION
Output Voltage Setting
The external resistor divider sets the output
voltage (see Typical Application Circuit on page
1). The feedback resistor (R1) also sets the
feedback loop bandwidth with the internal
compensation capacitor (see Typical Application
Circuit).
Choose R1 around 500kΩ for optimal transient
response. R2 is then given by:
R2 = R1
VOUT − 1
0.6V
Table 1—Resistor Selection vs. Output
Voltage Setting
VOUT
1.2V
1.5V
1.8V
2.5V
R1
499kΩ (1%)
499kΩ (1%)
499kΩ (1%)
499kΩ (1%)
R2
499kΩ (1%)
332kΩ (1%)
249kΩ (1%)
158kΩ (1%)
Inductor Selection
A 1µH to 10µH inductor with DC current rating
at least 25% higher than the maximum load
current is recommended for most applications.
For best efficiency, the inductor DC resistance
shall be <200mΩ. See Table 2 for
recommended inductors and manufacturers.
For most designs, the inductance value can be
derived from the following equation:
( ) L1 = VOUT × VIN − VOUT
VIN × ∆IL × fOSC
where ∆IL is the Inductor Ripple Current.
Choose inductor ripple current approximately
30% of the maximum load current, 1A.
The maximum inductor peak current is:
IL(MAX)
= ILOAD
+
∆IL
2
Under light load conditions below 100mA, larger
inductance is recommended for improved
efficiency. Table 3 lists inductors recommended
for this purpose.
MP2112 Rev. 1.2
www.MonolithicPower.com
6
3/6/2006
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2006 MPS. All Rights Reserved.
Share Link: 