MP29373 — DUAL 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER

MP29373 Rev. 1.1

www.MonolithicPower.com

5

12/13/2007

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2007 MPS. All Rights Reserved.

OPERATION

The MP29373 is a dual channel current mode

regulator. The COMP pin voltage is proportional

to the peak inductor current. At the beginning of

a cycle, the upper transistor M1 is off, and the

lower transistor M2 is on (see Figure 1). 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

Amplifier. Ramp compensation is summed to

Current Sense Amplifier output and compared

to the Error Amplifier output by the Current

Comparator.

When the sum of the Current Sense Amplifier

output and the Slope Compensation signal

exceeds the COMP pin voltage, the RS Flip-

Flop is reset. The MP29373 reverts to its initial

M1 off, M2 on state.

If the sum of the Current Sense Amplifier output

and the Slope Compensation signal does not

exceed the COMP voltage, 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 0.92V bandgap reference. The polarity is

such that a voltage at the FB pin lower than

0.92V 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 (see Figure 1).

LOCKOUT

COMPARATOR

ERROR

AMPLIFIER

FREQUENCY

FOLDBACK

COMPARATOR

INTERNAL

REGULATORS

1.8V

SLOPE

COMP

CLK

CURRENT

COMPARATOR

CURRENT

SENSE

AMPLIFIER

SHUTDOWN

COMPARATOR

SSA/

SSB

OSCILLATOR

210/1400KHz

S

R

Q

5V

+

Q

0.7V

+

+

2.29V/

2.50V

+

0.4V

+

+

--

--

--

--

--

--

0.92V

COMPA/

COMPB

FBA / FBB

SGA/

SGB

PGA/

PGB

SWA/

SWB

BSA/

BSB

ENA/

ENB

INA/

INB

Figure 1—Functional Block Diagram

(Diagram portrays ½ of the MP29373)