3 Boost UVP Design Consideration

When V_{BOOST_UVP} is reached, in other words, when V_FB is below V_UVP of 0.886 V, it is a sign that the boost is no longer in regulation. During normal operation, V_FB is regulated at V_BG of 1.21 V. If undervoltage condition lasts longer than 110 ms, LP8863-Q1 (using LP8863-Q1 as an example and it is similar for LP886x-Q1) will report boost overcurrent, by generating fault interrupt and asserting BSTOCP_STATUS bit in INTERRUPT_STATUS_1 register, as shown in Table 3-1. The device will go to standby for 200 ms before restart attempt. If V_{BOOST_UVP,MAX} (when I_SEL is at maximum value) level is lower than (V_STRING + V_HEADROOM,MAX), open LED fault may be reported unintentionally instead of overcurrent fault during an overcurrent event. Therefore, we recommend to design the maximum boost UVP threshold V_{BOOST_UVP,MAX} when the current DAC I_SEL is at maximum value, higher than V_STRING,MAX + V_HEADROOM,MAX, as shown in Equation 4. The aim is to prevent false triggering of LED open fault during an overcurrent event when boost under voltage is detected.

Equation 3.