TM
MP2106 – 1.5A, 15V, 800KHz SYNCHRONOUS BUCK CONVERTER
The MP2106 measures the output voltage
through an external resistive voltage divider and
compares that voltage to the internal 0.9V
reference in order to generate the error voltage
at COMP. The current-mode regulator uses the
voltage at COMP and compares it to the
inductor current to regulate the output voltage.
The use of current-mode regulation improves
transient response and improves control loop
stability.
switch, forcing the inductor current to decrease.
The average inductor current is controlled by
the voltage at COMP, which in turn is controlled
by the output voltage. Thus the output voltage
controls the inductor current to satisfy the load.
Since the high-side N-Channel MOSFET
requires voltages above VIN to drive its gate, a
bootstrap capacitor from LX to BST is required
to drive the high-side MOSFET gate. When LX
is driven low (through the low-side MOSFET),
the BST capacitor is internally charged. The
voltage at BST is applied to the high-side
MOSFET gate to turn it on, and maintains that
voltage until the high-side MOSFET is turned
off and the low-side MOSFET is turned on, and
the cycle repeats. Connect a 10nF or greater
capacitor from BST to SW to drive the high-side
MOSFET gate.
At the beginning of each cycle, the high-side
N-Channel MOSFET is turned on, forcing the
inductor current to rise. The current at the drain
of the high-side MOSFET is internally
measured and converted to a voltage by the
current sense amplifier.
That voltage is compared to the error voltage at
COMP. When the inductor current rises
sufficiently, the PWM comparator turns off the
high-side switch and turns on the low-side
APPLICATION INFORMATION
C7
10nF
INPUT
2.6V to 15V
7
6
VIN
BST
5
8
2
OUTPUT
1.8V / 1.5A
RUN
LX
FB
1
3
SS
COMP
MP2106
VREF SGND PGND
C5
10nF
C3
3.3nF
4
10
9
C4
OPEN
C6
10nF
MP2106_TAC_F02
Figure 2—Typical Application Circuit
Internal Low-Dropout Regulator
Soft-Start
The internal power to the MP2106 is supplied
from the input voltage (VIN) through an internal
2.4V low-dropout linear regulator, whose output
is VREF. Bypass VREF to SGND with a 10nF
or greater capacitor for proper operation. The
internal regulator can not supply more current
than is required to operate the MP2106.
Therefore, do not apply any external load to
VREF.
The MP2106 includes a soft-start timer that
slowly ramps the output voltage at startup to
prevent excessive current at the input.
When power is applied to the MP2106, and
RUN is asserted, a 2µA internal current source
charges the external capacitor at SS. As the
capacitor charges, the voltage at SS rises. The
MP2106 internally limits the feedback threshold
voltage at FB to that of the voltage at SS. This
forces the output voltage to rise at the same
rate as the voltage at SS, forcing the output
MP2106 Rev. 1.6
2/22/2006
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