mic4102 Micrel Semiconductor, mic4102 Datasheet - Page 15

• Manufacturer Part Number: mic4102
• Description: 100v Half Bridge Mosfet Driver With Anti-shoot Through Protection
• Manufacturer: Micrel Semiconductor

Current in the high-side driver is sourced from capacitor
C
the gate of the high side MOSFET. The return path for
the current is from the source of the MOSFET and back
to capacitor C
does not have a low impedance ground plane so the
etch connections in this critical path should be short and
wide to minimize parasitic inductance. As with the low-
side circuit, impedance between the MOSFET source
and the decoupling capacitor causes negative voltage
feedback which fights the turn-on of the MOSFET.
It is important to note that capacitor CB must be placed
close to the HB and HS pins. This capacitor not only
provides all the energy for turn-on but it must also keep
HB pin noise and ripple low for proper operation of the
high-side drive circuitry.
Figure 10 shows the critical current paths when the
driver outputs go low and turn off the external
MOSFETs. Short, low impedance connections are
important during turn-off for the same reasons given in
the turn-on explanation.
internal diode replenishes charge in the bootstrap
capacitor, CB.
Micrel, Inc.
November 2006
B
and flows into the HB pin and out the HO pin, into
High-side drive turn-on
current path
plane
gnd
Figure 9. Turn-on Current Paths
B
. The high-side circuit return path usually
Low-side drive turn-on
C
current path
Vdd
C
B
Vdd
HB
HO
HS
Current flowing through the
Level
shift
_
Q
Q
Vss
LO
LO
FF
LS
PWM
plane
gnd
15
The following circuit guidelines should be adhered to for
optimum circuit performance:
1. The Vcc and HB bypass capacitors must be
2. A ground plane should be used to minimize
3. Trace out the high di/dt and dv/dt paths, as
Charge C
internal diode when
High-side drive turn-off
HS pin is low
placed close to the supply and ground pins. It is
critical that the etch length between the high
side decoupling capacitor (C
pins be minimized to reduce lead inductance.
parasitic inductance and impedance of the
return paths. The MIC4102 is capable of greater
than 3A peak currents and any impedance
between
capacitors and the external MOSFET will
degrade the performance of the driver.
shown in Figures 9 and 10 to minimize the etch
length and loop area for these connections.
Minimizing these parameters decreases the
parasitic inductance and the radiated EMI
generated
A typical layout of a synchronous Buck converter
power stage using the MIC4102 (Figure 11) is
shown in Figure 12.
current path
B
Figure 10. Turn-off Current Paths
through
C
the
Vdd
by
C
B
fast
MIC4102,
HO
HB
Vdd
HS
rise
Level
shift
B
) and the HB & HS
and
the
Low-side drive turn-off
_
Q
Q
Vss
M9999-112806
LO
LO
FF
LS
current path
fall
decoupling
MIC4102
PWM
times.