¡ Semiconductor

MSC1201-xx

13/20

PWM Conversion

In the PWM conversion mode, "lamp PWM", which is used for dimming control of back-light for

instrument clusters or other displays, is used to generate the PWM signal for VFD tube dimming

control. The lamp PWM input to "PWM IN" pin is converted to PWM signal for VFD tube with

a built-in PWM conversion look-up table (User-Programmable Mask ROM).

A

PWMIN

B5V

PWM Input Frequency = 256 ± 80Hz

Duty Cycle = A / (A+B)

Note: The duty cycle of the lamp PWM signal is measured with a reference point of 2.5 V typ.

As the reference point of 2.5 V is the threshold voltage of "PWM IN" pin, it deviates to

some value between 0.8 V and 3.8 V due to process parameter deviation. Therefore, the

PWM conversion error increases as the rise/fall time of the lamp PWM increases.

GRID/SEG Driver Operation and Digital/Analog Dimming Operation

Figure 6 shows an output timing of the GRID and SEG Driver when the VK is "H" level.

Output timings of the GRID and SEG drivers are shown in figure 7 for the digital dimming mode

operation in figure 8 for the PWM conversion mode operation.

(1) GRID and SEG drivers output timings when VK = "H"

GRID1

GRID2

SEG1-30

1 Frame (4096-bit times)

16-bit times

2032-bit times

6-bit times

2038-bit times

10-bit times

Fig. 6 GRID and SEG Output Timing (VK = "H")