ST7FLCD1 datasheet(45/95 Pages) STMICROELECTRONICS

Teilenummer	ST7FLCD1

Bauteilbeschribung	8-bit MCU for LCD Monitors with 60 KBytes Flash,2 KBytes RAM, 2 DDC Ports and Infrared Controller

PDF	95 Pages

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Hersteller	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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ST7FLCD1

PWM Generator

Equations:

This Pulse Width modulated signal must be filtered, using an external RC network placed as close

as possible to the associated pin. This provides an analog voltage proportional to the average

charge through the external capacitor. Thus for a higher mark/space ratio (High time much greater

than Low time) the average output voltage is higher. The external components of the RC network

should be selected for the filtering level required for control of the system variable.

With:

REXT = 1 kΩ

fPWM = fCPU / (256 - ARR)

fCPU = 8 MHz

VDD = 5 V

Worst case, PWM Duty Cycle 50%

Table 16: Pulse WIdth in tCPU

Pulse WIdth in tCPU

DCR

≥ ARR

DCR - ARR + 1

DCR = ARR

DCR < ARR

0 (Output will not toggle)

Table 17: 8-bit PWM Ripple after Filtering

CEXT

VRIPPLE

470 nF

60 mV

1µF

27mV

4.7 µF

6 mV

Duty Cycle =

DCR + 1

256 - ARR

VRIPPLE =

(1 - e 1/(2 x CEXT x REXT x fPWM))2

|1 - e 1/(CEXT x REXT x fPWM)|

x VDD

ST7FLCD1 Datenblatt(PDF) 45 Page - STMicroelectronics