L6911E Просмотр технического описания (PDF) - STMicroelectronics

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L6911E

5-Bit programmable step down controller with synchronous rectification

STMicroelectronics 

L6911E

Device description

As shown in Figure 8 on page 18, the ESR drop is present in any case, but using the droop

function the total deviation of the output voltage is minimized. In practice the droop function

introduces a static error (Vdroop in Figure 8 on page 18) proportional to the output current.

Since a sense resistor is not present, the output DC current is measured by using the

intrinsic resistance of the inductance (a few mΩ). So the low-pass filtered inductor voltage

(that is the inductor current) is added to the feedback signal, implementing the droop

function in a simple way. Referring to the schematic in Figure 9, the static characteristic of

the closed loop system is:

Equation 13

VOUT

=

VPR

O

G

+

VP

R

O

G

⋅

R-----3-----+-----R-----8-----/--/---R-----9-

R2

–

-R----L----⋅---R-----8------/-/----R----9--

R8

⋅

IOU

T

Where VPROG is the output voltage of the digital to analog converter (i.e. the set point) and

zReLroislothaedin(∆dVu+c)t;atnhceethreirsdisttearnmcein. tTrohdeusceecsotnhde

term of the equation allows a positive offset at

droop effect (∆VDROOP). Note that the droop

effect is equal the ESR drop if:

Equation 14

-R----L----⋅---R-----8------/-/----R----9-- = ESR

R8

Figure 9. Compensation network

V IN

V COM P

C18

ZF

V PROG

PW M

C 20

R4

R3

R2

V PHASE

L2

RL

R8

R9

C 25

ZI

V OUT

ESR

C 6-15

19/34

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