In the application note for ILD8150 at chapter 2.2.7 I read:
The high-side MOSFET gate driver is supplied by the bootstrap circuit. Capacitor CBOOT is charged when the high-side MOSFET is switched off and the diode D conducts current from VCC. CBOOT can be calculated as:
𝐶𝐵𝑂𝑂𝑇 > 𝑄𝐺 / ∆𝑉𝐶𝑏𝑜𝑜𝑡
Where QG is the internal MOSFET gate charge, 2.5nC and ∆VCBOOT is voltage deviation on the bootstrap capacitor.The internal supply circuit provides voltage to the bootstrap capacitor VCboot ≈ 8.6 V,which is a little higher than VCC. This circuit helps to maintain the voltage in dim-to-off and standby conditions. Higher voltage improves the RON of the internal MOSFET.
I understand that VCboot is 8.6 V, but what do they mean with "delta" in this context? Perhaps the voltage across Cboot? VCBoot - VCC = 8.6 V - 7.3 V = 1.3 V
Both values are constant, so why do they provide the formula only and not the recommended value for the capacitor? I mean, I cannot change the QG neither ∆𝑉𝐶𝑏𝑜𝑜𝑡, can I?