MP1470 – SYNCHRONOUS, STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
OPERATION
The MP1470 is a high-frequency, synchronous,
rectified, step-down, switch-mode converter
with internal power MOSFETs. It offers a very
compact solution to achieve a 2A continuous
output current over a wide input supply range,
with excellent load and line regulation.
Under the light load condition, the value of
VCOMP is low. When VCOMP is less than VAAM and
VFB is less than VREF, VCOMP ramps up until it
exceeds VAAM. During this time, the internal
clock is blocked, thus the MP1470 skips some
pulses for PFM (Pulse Frequency Modulation)
mode and achieves the light load power save.
The MP1470 operates in a fixed-frequency,
peak-current–control mode to regulate the
output voltage. An internal clock initiates the
PWM cycle to turn on the integrated high-side
power MOSFET. This MOSFET remains on
until its current reaches the value set by the
COMP voltage. When the power switch is off, it
remains off until the next clock cycle starts. If
the current in the power MOSFET does not
reach the COMP set current value within 90%
of one PWM period, the power MOSFET is
forced to turn off.
Clock
V
OUT
1.2pF
V
AAM
V
+
HS_driver
47pF 500k
Q
S
R
R1
V
-
20k
COMP
-
FB
+
R2
-
V
REF
V
+
IL sense
Figure 2: Simplified AAM Control Logic
When the load current is light, the inductor peak
current is set internally to about 380mA for
VIN=12V, VOUT=3.3V, and L=6.5μH. The curve
of inductor peak current vs. inductor is shown in
Figure 3.
Internal Regulator
The 5V internal regulator powers most of the
internal circuits. This regulator takes VIN and
operates in the full VIN range. When VIN
exceeds 5.0V, the regulator output is in full
regulation. When VIN falls below 5.0V, the
output decreases.
Inductor Peak Current
vs. Inductor
1.2
1.1
1
Error Amplifier
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
The error amplifier compares the FB voltage
against the internal 0.8V reference (REF) and
outputs a current proportional to the difference
between the two. This output current charges or
discharges the internal compensation network
to form the COMP voltage, which is used to
control the power MOSFET current. The
optimized internal compensation network
minimizes the external component counts and
simplifies the control-loop design.
0
1
2
3
4
5
6
7
Figure 3: Inductor Peak Current vs. Inductor
Value
AAM Operation
Enable
The
MP1470
has
AAM
(Advanced
EN is a digital control pin that turns the
regulator on and off: Drive EN HIGH to turn on
the regulator, drive it LOW to turn it off. An
internal 1Mꢀ resistor from EN to GND allows
EN to float to shut down the chip.
Asynchronous Modulation) power-save mode
for light load. The AAM voltage is set at 0.5V
internally. Under the heavy load condition, the
VCOMP is higher than VAAM. When the clock goes
high, the high-side power MOSFET turns on
and remains on until VILsense reaches the value
set by the COMP voltage. The internal clock
resets every time when VCOMP is higher than
The EN pin is clamped internally using a 6.5V
series-Zener-diode as shown in Figure 4.
Connecting the EN input pin through a pullup
VAAM
.
MP1470 Rev. 1.02
8/27/2013
www.MonolithicPower.com
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