7

Date: 9/25/06 Rev C

SP6659 1.5MHz, 600mA Synchronous Buck Regulator

© 2006 Sipex Corporation

Figure 21. SP6659 Idle Mode Operation

APPLICATION INFORMATION

A resistive divider based on the following

equation determines the output voltage:

)

The external resistive divider is connected

to the output as shown in Figure 20 .

®

SP6659

GND

R1

R2

Figure 20: Setting the SP6659 Output Voltage.

R1

R2

The SP6659 is a monolithic switching mode

Step-Down DC-DC converter. It utilizes in-

ternal MOSFETs to achieve high efficiency

and can generate very low output voltage

by using its internal reference at 0.6V. It

operates at a fixed switching frequency,

and uses slope compensated, current-mode

architecture. This Step-Down DC-DC con-

verter supplies 600mA of output current at

from 2.5V to 5.5V.

__________________ CURRENT MODE

PWM CONTROL

Slope compensated current mode PWM

control provides stable switching and cycle-

by-cycle current limit for excellent load and

line responses and protection of the internal

main switch (P-Channel MOSFET) as well

as the synchronous rectifier (N-Channel

MOSFET). During normal operation, the in-

ternal P-Channel MOSFET is turned on for

a certain time to ramp the inductor current at

each rising edge of the internal oscillator,

and switched off when the peak inductor

current is above the error voltage.

The

inductor current. When the main switch is

off, the synchronous rectifier will be turned

THEORY OF OPERATION

on immediately and stay on until either the

inductor current starts to reverse, as indi-

cated by the current reversal comparator,

cycle.

The OVDET comparator controls

output transient overshoots by turning the

main switch off and keeping it off until the

fault is no longer present.

_______________________ IDLE MODE

OPERATION

At very light loads, the SP6659 automati-

cally enters Idle Mode (Figure 21).

_____________________ SETTING THE

OUTPUT VOLTAGE