MP3115 – HIGH-EFFICIENCY 1.3MHz SYNCHRONOUS STEP-UP CONVERTER

MP3115 Rev. 0.9

www.MonolithicPower.com

6

4/12/2016

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OPERATION

GND

SW

OUT

CONTROL

LOGIC

RSENSE

CURRENT

SENSE

AMPLIFIER

PWM

COMPARATOR

+

RAMP

OSC

1.3MHz

BIAS

STARTUP

SOFT-START

PROTECTION

ERROR

AMPLIFIER

FB

EN

2

1

5

4

IN 6

3

Figure 1—Functional Block Diagram

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.

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 through the internal P-Channel

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.