L9305QFP datasheet(21/107 Pages) STMICROELECTRONICS

21 / 107 page

A set of parameters for the loop control is available through SPI registers in order to tune the transient response

and settling time of the loop based on the user’s load characteristics. These settings and details are discussed in

the following sections.

6.1.4

Fixed frequency control

The fixed frequency control subtracts the current measurement signal from the programmed set point to create

the error signal. The proportional and integral amplifiers process the error signal and generate the

PROPORTIONAL and INTEGRAL signals. The processing of PROPORTIONAL and INTEGRAL signals depends

on the user programmed values of Kp and Ki in the Channel_x.KGAINS register. The control loop then adds

PROPORTIONAL and INTEGRAL signals and compares the result with ramp generator.

Figure 10. Fixed frequency algorithm

(*) Programmable parameter.

(**) The integrator limiter is automatically calculated for Fixed Frequency algorithm. It avoids that the PI signal

exceeds the max. and min. levels of the RAMP signal. This allows fastest loop transient response.

(*)

Comparator

Integrator

Limiter

Z –1

Ramp

Generator

Current

Set Point

Current

Measurement

–

PWM

(**)

(*)

PROPORTIONAL

INTEGRAL

RAMP

GADG2709181213PS

The LIMITER in the integral path, limits the integral signal automatically to the RAMP signal to ensure the fastest

PWM changes to reduce current over and under shoot. An example of current control block diagram is shown in

Figure 10.

L9305

Current control drivers

DS12774 - Rev 10

page 21/107

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