ISL6615A_14 Datasheet, PDF (9/12 Pages) Intersil Corporation – High-Frequency 6A Sink Synchronous MOSFET Drivers with Protection Features

ISL6615A
gate-source threshold of the upper MOSFET. A higher dV/dt, a
lower C_DS/C_GS ratio, and a lower gate-source threshold upper
FET will require a smaller resistor to diminish the effect of the
internal capacitive coupling. For most applications, the
integrated 20kΩ typically sufficient, not affecting normal
performance and efficiency.
The coupling effect can be roughly estimated with the formulas
in Equation 5, which assume a fixed linear input ramp and
neglect the clamping effect of the body diode of the upper drive
and the bootstrap capacitor. Other parasitic components such as
lead inductances and PCB capacitances are also not taken into
account. These equations are provided for guidance purpose
only. Therefore, the actual coupling effect should be examined
using a very high impedance (10MΩ or greater) probe to ensure
a safe design margin.
⎛
---------–---^V----^D----^S-----------⎞
V _{G S _MILLER}
=
d_----V_--
dt
⋅
R
⋅
⎜
C_{r s s ⎜⎜} 1
⎜
–
d_----V_--
e ^dt
⋅
R
⋅
Ci
⎟
s s⎟
⎟
⎟
⎝
⎠
(EQ. 5)
R = R_UGPH + R_GI
C_rss = C_GD
C_iss = C_GD + C_GS
PVCC
DU
DL
BOOT
C_BOOT
UGATE G
PHASE
C_GD
VIN
D
C_DS
R_GI
C_GS
S
Q_UPPER
FIGURE 5. GATE-TO-SOURCE RESISTOR TO REDUCE UPPER
MOSFET MILLER COUPLING
9
FN6608.2
April 13, 2012