L9305 datasheet(23/107 Pages) STMICROELECTRONICS

23 / 107 page

Figure 12. Variable frequency algorithm

Limit

INTEGRAL

ZERO

1.1

1.05

0.95

0.9

2000

10.9

1.1

11.1

11.2

Time (ms)

11.3

11.4

11.5

11.6

-2000

-4000

F_INTEGRAL

Z –1

Current Control

Current

Set Point

Current

Set Point

Current

Measurement

–

F_Integrator

Initial

Z –1

KFI

Comp

State

machine

SET

PWM

RES

Frequency Control

PWM Period

Set Point

Current

Measurement

–

Set Point Change

Long Period Detection

–

Comp

PWM

Load Current

–

Integrator

GADG2709181227PS

In transient mode the integrator limits the INTEGRAL signal within user programmable limits, this guarantees the

fastest current transitions between different set points without showing over/undershoot. The integrator limits of

variable frequency control are not automatically calculated; the user-programmed parameters POSINTLIM and

NEGINTLIM are available for optimized positive and negative integrator limits.

In transient mode the F_INTEGRAL signal at the frequency integrator output is set to a programmable value with

the 3 control bits FINT_START (D[2:0] in KFREQCTRL register), in this way the F_INTEGRAL signal starts close

to its final value when exiting from transient mode.

To optimize the controller response for different applications, the following parameters must be programmed by

the user:

•

KI (Channel_x.KGAINS)

•

KFI (Channel_x.KFREQCTRL)

•

POSINTLIM & NEGINTLIM (Channel_x.INTGLIM)

•

Auto Limit (Channel_x.SETPOINT)

•

Transition Time (Channel_x.CTRLCFG)

•

Fint_Start (Channel_x.KFREQCTRL)

Programming values can be selected considering the following:

•

KI: Integral portion of the loop gain. It can be calculated as

KI=2KIsel

•

KFI: Integral portion of the frequency control loop gain. It can be calculated as

KFI=2KFIsel

•

POSINTLIM: Positive Integrator Saturation Limit. It can be calculated as

POSINTLIM=2POSINTLIMsel−1

•

NEGINTLIM: Negative Integrator Saturation Limit. It can be calculated as

NEGINTLIM=−2NEGINTLIMsel−1

•

AUTO_LIMIT:

–

If AUTOL_LIMIT_SEL = 0 → Transient mode is insensitive to changes of Current Set Point

–

If AUTOL_LIMIT_SEL = 1 → Any change in the current set point activates the transient mode

•

FINIT_START:

–

If FINIT_START_SEL = 0 →

FINITSTART=0

–

If FINIT_START_SEL >0 →

FINITSTART=NEGINTLIM*2FINITSTARTsel−7

L9305

Current control drivers

DS12774 - Rev 10

page 23/107

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