PCF8536AT1 datasheet(45/74 Pages) NXP

45 / 74 page

PCF8536

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Product data sheet

Rev. 2 — 21 February 2012

45 of 74

NXP Semiconductors

PCF8536

Universal LCD low multiplex driver with 6 channel PWM generator

8.11.2 PWM inversion mode

The PWM inversion mode can be enabled by setting the PWMI bit to logic 1 (see Table 7

on page 8). The PWMI mode will invert the PWM waveform.

By default, all PWM outputs will switch HIGH at the same time. If the PWM output is used

to drive external LEDs then this could cause a voltage dip on the power supply of the

LEDs. With the PWMI mode, it is possible to prevent multiple outputs switching HIGH at

the same time by ensuring that the PWM values are not identical.

In the example in Figure 30, none of the six PWM outputs switch HIGH together. All PWM

channels instead switch off together; however this will not cause any power supply

disturbances.

When PWM inversion mode is used, the PWM duty cycle can be calculated with:

(10)

Fig 30. PWM example waveforms for PWMI = 1

001aan570

fPWM

PWM register 0 = 0

100.00 %

99.20 %

75.00 %

50.00 %

25.00 %

0.78 %

PWM register 1 = 1

PWM register 2 = 32

PWM register 3 = 64

PWM register 4 = 96

PWM register 5 = 127

t =

128 x fPWM

DutyCycle

128

PWMvalue

–

128

-------------------------------------------- 100

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