We use LP8860 for our LCD backlight in the display mode 4-Channels (Mode 0) and would like to sync the boost switching frequency to an external clock of 1.8MHz and program the EEPROM to use 1.111MHz when the external clock disappears. I have tested this condition and seems to work fine, I do not see the LED's flicker when the external clock disappears and the controller falls back to the programmed 1.111MHz.
However going over the data sheet, "If an external SYNC disappears, boost uses internal frequency defined by <BOOST_FREQ_SEL[2:0]> EEPROM bits. The boost frequency with external SYNC and EEPROM bits-defined frequency need to be close to each other; maximum frequency mismatch is ±25%."
We strictly want to use 1.8MHz for the boost switching frequency but it does not fall within the +/- 25% of internal clock setting of 1.111MHz. The next available setting for the internal clock is 2.5MHz for which the 1.8MHz will be much closer to the +/- 25% condition but the switching FET heats up when 2.5MHz is used.
Please advise if we can use external sync clock of 1.8MHz with internal clock set to 1.111MHz and have no issue during normal operation when the SYNC clock disappears and re-appears.
Thank you for your assistance on this.
