L6911E Просмотр технического описания (PDF) - STMicroelectronics

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L6911E

5-Bit programmable step down controller with synchronous rectification

STMicroelectronics 

Device description

L6911E

Considering the previous relationships R2, R3, R8 and R9 may be determined in order to

obtain the desired droop effect as follow:

● Choose a value for R2 in the range of hundreds of KΩ to obtain realistic values for the

other components.

● From the above equations, it results:

Equation 15

R8

=

∆-----V----+----⋅---R-----2-

VPROG

⋅

∆--R--V--L--D--⋅--R-I--M-O---A-O---X-P-

Equation 16

R9

=

R8

⋅

∆----V----D----R----O----O----P-

RL ⋅ IMAX

⋅

-----------------1------------------

1 + ∆--R--V--L--D--⋅--R-I--M-O---A-O---X-P-

Where IMAX is the maximum output current.

● The component R3 must be chosen in order to obtain R3 << R8//R9 to permit these

and successive simplifications.

Therefore, with the droop function the output voltage decreases as the load current

increases, so the DC output impedance is equal to a resistance ROUT. It is easy to verify that

the output voltage deviation under load transient is minimum when the output impedance is

constant with frequency.

20/34

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