8

Feb2-07 Rev O

SP7663 Wide Input Voltage Range 6A, 600kHz Buck Regulator

© 2007 Sipex Corporation

R9

26.4KΩ

CSP

6.8nF

SWN

ISP

ISN

SP7663

CS

0.1uF

R4

5.11KΩ

R3

5.11KΩ

L = 1.5uH, DCR = 9.2mΩ

Over-current detection circuit for

Decreasing the Current Limit

resistor is added as shown in the following

figure.R8increasesthenetvoltagedetected

by the current-sense comparator. Voltage at

the positive and negative terminal of com-

paratorisgivenby:

Sincethecomparatoristriggeredat60mV:

VSP-VSN = 60 mV

Combining the above equations and solv-

ingforR8:

R8 =

R4 •

calculatedR8is1.1MΩ.

CSP

6.8nF

ISN

SP7663

SWN

ISP

CS

0.1uF

R4

5.11KΩ

R3

5.11KΩ

L = 1.5uH, DCR = 9.2mΩ

R8

1.1MΩ

Over-current detection circuit for

Handling of Faults

Upon the detection of power (UVLO), ther-

mal, or short-circuit faults, the SP7663 is

forced into an idle state where the SS and

COMPpinsarepulledlowandbothswitches

are held off. In the event of UVLO fault, the

SP7663 remains in this idle state until the

UVLO fault is removed. Upon the detection

of a thermal or short-circuit fault, an internal

20ms timer is activated. In the event of a

short-circuit fault, a restart is attempted im-

mediately after the 20ms timeout expires.

Whereas, when a thermal fault is detected

the20msdelaycontinuouslyrecyclesanda

restartcannotbeattempteduntilthethermal

fault is removed and the timer expires.

Error Amplifier and Voltage Loop

The heart of the SP7663 voltage error loop

is a high performance, wide bandwidth

transconductance amplifier. Because of

THEORY OF OPERATION