I am using a PTN3460IBS with a Q7 system on module equipped with an Intel E3845 to provide two display outputs. The primary display is connected to the dual LVDS interface of the Q7 module (sourced from an ANX1122 eDP to LVDS bridge). The second display is connected to via the PTN3460IBS configured as a dual LVDS interface. The PTN3460IBS is configured as master mode with the EDID and configuration in external EEPROM. We initially failed to get the backlight on as there was no PWM output from the PTN3460IBS. The PWM bitcount at address 0x8F was set to 0x0A and PWM frequency at address 0x92 to 0x02 to obtain a PWM frequency of approximately 13kHz. With byte locations 0x8F, 0x92 changed back to 0x0C and 0x1E as per AN11128 we generated a PWM signal of around 220Hz and after some flickering managed to drive the display briefly.
The backlight driver board we are using requires a DC signal for operation so we are using a low pass filter to derive the signal from the PWM output. The low pass filter has a 3dB cutoff of around 80Hz so we are seeing quite a bit of ripple on the backlight control signal. Can you provide guidance as to the limits of the PWM output frequency ? Is there a more detailed description of the PTN3460IBS registers other than AN11128 ? I would like to understand how to configure the device correctly to achieve the optimum solution.