MP1517 – 3A, 25V, 1.1MHz STEP-UP CONVERTER

MP1517 Rev. 1.4

www.MonolithicPower.com

5

4/28/2006

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© 2006 MPS. All Rights Reserved.

OPERATION

The MP1517 uses a 1.1MHz fixed-frequency,

current-mode regulation architecture to regulate

the output. The operation of the MP1517 can be

understood by referring to the block diagram of

Figure 1. 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 at COMP. The

voltage at the output of the error amplifier is an

amplified version of the difference between the

700mV reference voltage and the feedback

voltage. When these two voltages are equal,

the PWM comparator turns off the switch

forcing the inductor current to the output

capacitor through the external rectifier. This

causes the inductor current to decrease. The

peak inductor current is controlled by the

voltage at COMP, which in turn is controlled by

the output voltage. Thus the output voltage

controls the inductor current to satisfy the load.

The use of current-mode regulation improves

transient response and control loop stability.

PWM

CONTROL

LOGIC

CURRENT

SENSE

AMP

SOFT-START

OSCILLATOR

LDO

2.4V

--

+

GM

+

--

--

+

PGND

FB

COMP

SS

SGND

0.7V

SW

IN

8

--

+

OLS

16V

EN

BP

2.4V

0.9V

MP1517_BD01

3

4

7

15

1

16

9, 10

11, 12

5, 13

Figure 1—Functional Block Diagram