AN486 Datasheet, PDF (6/10 Pages) Silicon Laboratories – High-Side Bootstrap Design Using ISODrivers in Power Delivery Systems

AN486: High-Side Bootstrap Design Using ISODrivers in Power Delivery Systems
Bootstrap Operation
In this design, 99 nC of charge must be transferred into C_B within the minimum low-side on time t_L(MIN). Equation 4 calculates the cur-
rent required to meet this criterion:
From Equation 4, a maximum average current of 197 mA is required to fully refresh C_B at maximum duty cycle time. The average cur-
rent through diode D1 can be calculated using Equation 5:
The voltage rating of bootstrap diode D1 must be sufficiently high to stand-off the high-side MOSFET drain voltage and a current rating
(IF) greater than or equal to the maximum average current as calculated in Equation 5. It must also have a sufficiently fast reverse
recovery time to avoid momentarily sourcing current from the high-voltage drain supply into the lower voltage VDD supply. In addition,
the operating temperature of the system may require D1 to have low reverse leakage at high temperature.
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