L9800 datasheet(30/55 Pages) STMICROELECTRONICS

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7.3

PWM generator

The device has two independent PWM generators, which are defined as “PWM GEN” and “PWM LED” below.

The two PWM generators can be associated to one or more channels. It is possible to configure it with various

frequencies and duty cycle. For both refer to the same base frequency fINT (8 MHz typ.) even if two separate pre-

scalers can be defined.

7.3.1

Automatic PWM generator

The device has one independent automatic PWM generator that can be assigned to one or more channels and

can be programmed with different duty cycle and frequency. The PWM frequency is obtained by dividing the

internal clock base frequency fINT and can be set using CFG_1.PWM_DIV_GEN bits and adjusted through

CFG_2.FR_ADJ bits as described in the Table 12.

Table 12. Coefficient overview

CFG_2.FR_ADJ

Absolute delta to fINT divider

00B

01B

-13%

10B

+18%

11B

To configure the PWM generator, the user can set the following parameters:

1. Duty cycle (bits PWM_GEN_DC.DUTY_CYCLE)

8 bits are available to achieve 0.39% duty cycle resolution.

When the microcontroller programs a new duty cycle, the PWM generator waits until the previous cycle is

completed before using the new duty cycle (this happens also when the duty cycle is 100%) - the new duty

cycle is taken with the next PWM cycle, while the new duty cycle is immediately taken if the previous DC was

0%)

The maximum duty cycle achievable is 100% (PWM_GEN_DC.DUTY_CYCLE set to “11111111B”).

2. Frequency (bits CFG_1.PWM_DIV_GEN)

Using 2 bits it is possible to select the divider for fINT to achieve the needed duty cycle:

–

00B = PWM frequency is 122.5 Hz

–

01B = PWM frequency is 245.1 Hz

–

10B = PWM frequency is 490.2 Hz

–

11B = PWM frequency is 980.4 Hz

3. Mapping registers (PWM_SEL and PWM_MAP)

To correctly use the PWM generator:

•

Configure the channel output control and mapping register (PWM_SEL and PWM_MAP).

•

Write the duty cycle control register (PWM_GEN_DC) to enable the PWM generation.

L9800

Power stages

DS14041 - Rev 2

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