MP3115 MPS, MP3115 Datasheet - Page 6

• Manufacturer Part Number: MP3115
• Description: High-efficiency, Single-cell Alkaline, 1.3mhz Synchronous Step-up Converter With Output Disconnect
• Manufacturer: MPS

OPERATION
The MP3115 uses a 1.3MHz fixed-frequency,
current-mode regulation architecture to regulate
the output voltage. The MP3115 measures the
output voltage through an external resistive
voltage divider and compares that to the
internal 1.2V reference to generate the error
voltage. The current-mode regulator compares
the error voltage to the inductor current to
regulate the output voltage. The use of current-
mode regulation improves transient response
and control loop stability.
When the MP3115 is disabled (EN<0.4V), both
power switches are off. The body of the
P-Channel MOSFET connects to SW thus there
is no current path from SW to OUT. When the
MP3115 is enabled (EN>0.8V), the P-Channel
MOSFET turns on to charge the output
capacitor to a voltage close to the input voltage.
During this time, the gate of the P-Channel is
controlled to limit the chip power dissipation.
The MP3115 starts switching when the output
voltage is close to the input voltage. If the input
voltage is less than 1.6V, the MP3115 will start
with CCM (constant current mode) until the
output voltage crosses 1.6V. After that, the
soft-start circuit will take over to bring the output
voltage to the regulated value.
MP3115 Rev. 0.9
1/25/2008
EN
FB
IN 6
4
3
PROTECTION
SOFT-START
STARTUP
BIAS
MP3115 – HIGH-EFFICIENCY 1.3MHz SYNCHRONOUS STEP-UP CONVERTER
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
AMPLIFIER
ERROR
Figure 1—Functional Block Diagram
1.1MHz
RAMP
OSC
+
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www.MonolithicPower.com
COMPARATOR
PWM
At the beginning of each cycle, the N-channel
MOSFET switch is turned on, forcing the
inductor current to rise. The current at the
source of the switch is internally measured and
converted to a voltage by the current sense
amplifier. That voltage is compared to the error
voltage. When the inductor current rises
sufficiently, the PWM comparator turns off the
switch, forcing the inductor current to the output
capacitor
MOSFET rectifier, which forces the inductor
current to decrease. The peak inductor current
is controlled by the error voltage, which in turn
is controlled by the output voltage. Thus the
output voltage controls the inductor current to
satisfy the load.
The MP3115 has a temperature sensing circuit
to protect the part. The MP3115 turns off both
switches when the chip temperature reaches
150°C.
CONTROL
AMPLIFIER
CURRENT
LOGIC
SENSE
through
RSENSE
the
internal
5
1
2
P-Channel
OUT
SW
GND
6