SP7663 datasheet(8/19 Pages) SIPEX

8 / 19 page

Nov3-06 Rev L

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

Asanexample:ifdesiredIMAx is 9A, then

RS3 = 26.4kΩ.

RS3

26.4KΩ

CSP

6.8nF

SWN

ISP

ISN

SP7663

0.1uF

RS2

5.11KΩ

RS1

5.11KΩ

L = 1.5uH, DCR = 9.2mΩ

VOUT

Over-current detection circuit for

Imax > 60mV / DCR

Decreasing the Current Limit

If it is required to set IMAx < {60mV / DCR,

a resistor is added as shown in the follow-

ing figure. RS3 increases the net voltage

detected by the current-sense comparator.

Voltage at the positive and negative terminal

ofcomparatorisgivenby:

VSP = VOut + (IMAx • DCR)

VSN = VOut •

{RS3 / (RS2 +RS3)}

Sincethecomparatoristriggeredat60mV:

VSP-VSN = 60 mV

Combining the above equations and solv-

ing for RS3:

RS3 =

RS2 •

[VOut- 60mV + (IMAX• DCR)]

60mV - (IMAX • DCR)

Asanexample:forIMAxof5AandVOutof3.3V,

calculated RS3is1.1MΩ.

CSP

6.8nF

ISN

SP7663

SWN

ISP

0.1uF

RS2

5.11KΩ

RS1

5.11KΩ

VOUT

L = 1.5uH, DCR = 9.2mΩ

RS3

1.1MΩ

Over-current detection circuit for

Imax < {60mV / DCR}

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

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