LP8860-Q1 / Discharge Circuit

Hi Kuramochi-san,

For normal operation, it won't have any issues as LED driver will be turned off as well. But, as you mentioned, there may be flash happens if LED load is disconnected and reconnected, and current path through GND is made in a way during this mechanical connection.
Another one is pin damage by fast discharge of boost voltage. If boost is shorted to GND while it's charged, it may cause negative spike on SW node or other pins, and may cause damage on device. This usually happens when LED load is disconnected after LED off too soon(if LED load has GND connection) or unintentional touch to GND.
Recommended way to avoid this damage is to wait long enough time for discharge or ohmic discharge using power resistors like 100ohm ~ 1kohm.

Hope this helps,

Hi Kuramochi-san,

I think it depends on required discharge time.

If it is about 1s or 2s, you can use a simple resistor connection to GND.

For example, 40kohm is connected between boost out and GND, continuous current flow for 40V out will be 1mA, which is the expense of this discharge path.

And if boost output capacitance is ~20uF, I=C*dV/dT = 1mA = 20*10^-6*40/time. time = 0.8s, And this time is based on DC current 1mA value, so actual discharge time will be a little more than 1s.

If discharge time should be very fast(1s), there can be 2 methods.

- you can use lower resistance value as described above, but power loss will be higher in this case.

- Another method will be adding a FET to control this discharge path.

        EN --> inverter --> gate of NFET connected between boost out and GND through 1kohm or less

This discharge path will be enabled only when EN signal is disabled. One thing to consider for this method is PL FET needs to be used, otherwise, this discharge path will be enabled all the time when boost is disabled while its input is connected to battery or power source directly.

Hope this helps,