L6701 datasheet(25/44 Pages) STMICROELECTRONICS

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L6701

10 Output Voltage Positioning

25/44

10.5

Maximum Duty Cycle limitation

To provide proper time for current-reading in order to equalize the current carried by each

phase, the device implements a duty-cycle limitation. This limitation is not fixed but it is linearly

variable with the current delivered to the load as follow:

Duty Cycle limitation is variable with the delivered current to provide fast load transient

response at light load as well as assuring robust over-current protection.

Figure 10 shows the maximum output voltage that the device is able to regulate considering the

TON limitation imposed by the previous relationship. If the desired output characteristic crosses

the limited-TON maximum output voltage, the output resulting voltage will start to drop after the

cross-point. In this case, the output voltage starts to decrease following the resulting

characteristic (dotted in Figure 10) until UVP is detected or anyway until IISENx = 35µA.

Figure 10. Maximum Duty Cycle limitation

ON max

()

0.80 T

ISENx

µA

⋅

0.40 T

ISENx

µA

⋅

⎩

⎨

⎧

VOUT

0.40 VIN

Maximum Output Voltage

0.80 VIN

IOCP = 3 x IOCPx

(IISENx = 35µA)

IOUT

VOUT

0.40 VIN

Limited TON

0.80 VIN

IOCP = 3 x IOCPx

(IISENx = 35µA)

IOUT

Desired output Char.

UVP Threshold

Resulting Output Char.

Limted-TON Output Char.

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