MIC28512 Datasheet, PDF (21/34 Pages) Microchip Technology – 70V, 2A Synchronous Buck Regulator

4.6 Power Good (PG)
The power good (PG) pin is an open-drain output that
indicates logic-high when the output is nominally 90%
of its steady state voltage.
4.7 MOSFET Gate Drive
The Functional Block Diagram shows a bootstrap
circuit, consisting of D_BST, C_BST, and R_BST. This circuit
supplies energy to the high-side drive circuit. Capacitor
C_BST is charged, while the low-side MOSFET is on,
and the voltage on the SW pin is approximately 0V.
When the high-side MOSFET driver is turned on,
energy from C_BST is used to turn the MOSFET on. As
the high-side MOSFET turns on, the voltage on the SW
pin increases to approximately V_IN. Diode D_BST is
reverse-biased and C_BST floats high while continuing to
bias the high-side gate driver. The bias current of the
high-side driver is less than 10 mA, so a 0.1 μF to 1 μF
capacitor is sufficient to hold the gate voltage with
minimal droop for the power stroke (high-side
switching) cycle, i.e. ∆BST = 10 mA x 1.25 μs/0.1 μF =
125 mV. When the low-side MOSFET is turned back
on, C_BST is then recharged through the boost diode. A
30Ω resistor R_BST, which is in series with the BST pin,
is required to slow down the turn-on time of the
high-side N-channel MOSFET.
MIC28512
 2016 Microchip Technology Inc.
DS20005524A-page 21