MP3209 MPS, MP3209 Datasheet - Page 6

• Manufacturer Part Number: MP3209
• Description: 1.4mhz, 350ma Boost Converter
• Manufacturer: MPS

PIN FUNCTIONS
OPERATION
The MP3209 uses a fixed frequency, peak current
mode boost regulator architecture to regulate
voltage at the feedback pin. The operation of the
MP3209 can be understood by referring to the
block diagram of Figure 1. At the start of each
oscillator cycle the MOSFET is turned on through
the control circuitry. To prevent sub-harmonic
oscillations at duty cycles greater than 50 percent,
a stabilizing ramp is added to the output of the
current sense amplifier and the result is fed into
the negative input of the PWM comparator. When
this voltage equals the output voltage of the error
amplifier the power MOSFET is turned off. The
voltage at the output of the error amplifier is an
MP3209 Rev.0.93
9/21/2007
TSOT23-5
Pin #
FB
1
2
3
4
5
1.25V
UTQFN8
Pin #
MPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY
3, 7
8
5
6
4
2
R
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
C
AMPLIFIER
Name
GND
ERROR
SW
EN
NC
FB
IN
+
-
C
C
Figure 1—Functional Block Diagram
Function
Power Switch Output. SW is the drain of the internal MOSFET switch. Connect the
power inductor and output rectifier to SW. SW can swing between GND and 22V.
Ground.
Feedback Input. FB voltage is 1.25V. Connect a resistor divider to FB.
Regulator On/Off Control Input. A high input at EN turns on the converter, and a
low input turns it off. When not used, connect EN to the input source for automatic
startup. The EN pin cannot be left floating.
Input Supply Pin. Must be locally bypassed.
No Connect.
1.3MHz
OSC
© 2007 MPS. All Rights Reserved.
+
www.MonolithicPower.com
COMPARATOR
+
-
PWM
MP3209 – 1.4MHZ, 350mA BOOST CONVERTER
amplified version of the difference between the
1.25V bandgap reference voltage and the
feedback voltage. In this way the peak current
level keeps the output in regulation. If the
feedback voltage starts to drop, the output of the
error amplifier increases. This results in more
current to flow through the power MOSFET, thus
increasing the power delivered to the output.
The MP3209 has internal soft start to limit the
amount of input current at startup and to also
limit the amount of overshoot on the output. The
current limit is increased by a fourth every 40µs
giving a total soft start time of 120µs.
CONTROL
LOGIC
AMPLIFIER
CURRENT
SENSE
+
-
GND
SW
M1
6