TM
MP2305 – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
OPERATION
The converter uses internal N-Channel
MOSFET switches to step-down the input
voltage to the regulated output voltage. Since
the high side MOSFET requires a gate voltage
greater than the input voltage, a boost capacitor
connected between SW and BS is needed to
drive the high side gate. The boost capacitor is
charged from the internal 5V rail when SW is low.
FUNCTIONAL DESCRIPTION
The MP2305 is a synchronous rectified,
current-mode, step-down regulator. It regulates
input voltages from 4.75V to 23V down to an
output voltage as low as 0.923V, and supplies
up to 2A of load current.
The MP2305 uses current-mode control to
regulate the output voltage. The output voltage
is measured at FB through a resistive voltage
divider and amplified through the internal
transconductance error amplifier. The voltage at
the COMP pin is compared to the switch current
measured internally to control the output
voltage.
When the MP2305 FB pin exceeds 20% of the
nominal regulation voltage of 0.923V, the over
voltage comparator is tripped and the COMP
pin and the SS pin are discharged to GND,
forcing the high-side switch off.
+
CURRENT
2
IN
OVP
SENSE
AMPLIFIER
+
--
--
+
1.1V
0.3V
5V
RAMP
CLK
OSCILLATOR
100/340KHz
5
FB
1
3
BS
--
--
+
S
Q
Q
--
+
+
SW
R
CURRENT
COMPARATOR
8
6
SS
ERROR
AMPLIFIER
0.923V
COMP
4
GND
OVP
1.2V
+
--
2.5V
EN
IN
IN < 4.10V
EN OK
LOCKOUT
COMPARATOR
7
+
--
EN
INTERNAL
REGULATORS
5V
SHUTDOWN
COMPARATOR
1.5V
MP2305_F01_BD01
Figure 1—Functional Block Diagram
MP2305 Rev. 1.7
4/17/2006
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5
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