MP2351DQ MPS [Monolithic Power Systems], MP2351DQ Datasheet - Page 4

• Manufacturer Part Number: MP2351DQ
• Description: 1.5A, 23V, 1.4MHz Step-Down Converter
• Manufacturer: MPS [Monolithic Power Systems]

OPERATION
The MP2351 is a current mode regulator. That
is, the COMP pin voltage is proportional to the
peak inductor current. At the beginning of a
cycle: the upper transistor M1 is off; the lower
transistor M2 is on; the COMP pin voltage is
higher than the current sense amplifier output;
and the current comparator’s output is low. The
rising edge of the 1.4MHz CLK signal sets the
RS Flip-Flop. Its output turns off M2 and turns
on M1 thus connecting the SW pin and inductor
to the input supply. The increasing inductor
current is sensed and amplified by the Current
Sense
summed to Current Sense Amplifier output and
compared to the Error Amplifier output by the
Current Comparator. When the Current Sense
Amplifier plus Slope Compensation signal
exceeds the COMP pin voltage, the RS
MP2351 Rev. 1.5
1/6/2006
SYNC 10
EN 9
IN 4
Amplifier.
COMPARATOR
FREQUENCY
2.37V/
2.62V
FOLDBACK
0.7V
TM
+
--
--
+
Ramp
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
COMPARATOR
COMPARATOR
SHUTDOWN
REGULATORS
LOCKOUT
+
--
INTERNAL
0.7V
compensation
7
Figure 1—Functional Block Diagram
OSCILLATOR
1.23V
FB
180KHz/
1.4MHz
© 2006 MPS. All Rights Reserved.
--
+
www.MonolithicPower.com
AMPLIFIER
MP2351 – 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER
ERROR
SLOPE
COMP
CLK
is
8
AMPLIFIER
CURRENT
COMP
+
--
SENSE
Flip-Flop is reset and the MP2351 reverts to its
initial M1 off, M2 on state. If the Current Sense
Amplifier plus Slope Compensation signal does
not exceed the COMP voltage, then the falling
edge of the CLK resets the Flip-Flop.
The output of the Error Amplifier integrates the
voltage difference between the feedback and
the 1.230V bandgap reference. The polarity is
such that an FB pin voltage lower than 1.230V
increases the COMP pin voltage. Since the
COMP pin voltage is proportional to the peak
inductor current an increase in its voltage
increases current delivered to the output. The
lower 10Ω switch ensures that the bootstrap
capacitor voltage is charged during light load
conditions. External Schottky Diode D1 carries
the inductor current when M1 is off.
COMPARATOR
CURRENT
1.8V
S
R
+
--
Q
Q
5V
2
5
6
MP2351_BD01
BS
SW
GND
4