MIC4102_11 MIC [MIC GROUP RECTIFIERS], MIC4102_11 Datasheet - Page 11

• Manufacturer Part Number: MIC4102_11
• Description: 100V Half Bridge MOSFET Driver with Anti-Shoot Through Protection PRELIMINARY SPECIFICATIONS
• Manufacturer: MIC [MIC GROUP RECTIFIERS]

Applications Information
Power Dissipation Considerations
Power dissipation in the driver can be separated into
three areas:
•
•
•
Bootstrap Circuit Power Dissipation
Power dissipation of the internal bootstrap diode
primarily comes from the average charging current of the
C
Secondary sources of diode power dissipation are the
reverse leakage current and reverse recovery effects of
the diode.
The average current drawn by repeated charging of the
high-side MOSFET is calculated by:
The average power dissipated by the forward voltage
drop of the diode equals:
The value of V
through the diode, however, this current is difficult to
calculate because of differences in source impedances.
The peak current can either be measured or the value of
V
good approximation of diode power dissipation.
The reverse leakage current of the internal bootstrap
diode is typically 11uA at a reverse voltage of 100V and
125C.
typically much less than 1mW and can be ignored.
Reverse recovery time is the time required for the
injected minority carriers to be swept away from the
depletion region during turn-off of the diode.
dissipation due to reverse recovery can be calculated by
computing the average reverse current due to reverse
recovery charge times the reverse voltage across the
diode.
dissipation due to reverse recovery can be estimated by:
Micrel, Inc.
November 2006
F
B
at the average current can be used and will yield a
capacitor times the forward voltage drop of the diode.
Internal diode dissipation in the bootstrap circuit
Internal driver dissipation
Quiescent current dissipation used to supply the
internal logic and control functions.
I
Pdiode
I
Pdiode
where
where
where
F
RR
(
AVE
(
AVE
Power dissipation due to reverse leakage is
The average reverse current and power
)
:
:
I :
fwd
RR
f
t
Q
V
)
=
S
RRM
rr
F
=
gate
Q
=
=
=
=
=
2
gate
F
gate
Reverse
I
I
×
Diode
RR
=
F
should be taken at the peak current
=
I
(
Peak
RRM
AVE
×
(
Total
AVE
drive
f
S
)
forward
×
)
×
Reverse
Recovery
Gate
×
t
V
switching
rr
V
F
REV
×
Charge
f
S
voltage
Recovery
Time
frequency
at
drop
V
HB
Current
Power
11
The total diode power dissipation is:
An optional external bootstrap diode may be used
instead of the internal diode (Figure 5).
diode may be useful if high gate charge MOSFETs are
being driven and the power dissipation of the internal
diode is contributing to excessive die temperatures. The
voltage drop of the external diode must be less than the
internal diode for this option to work.
voltage across the diode will be equal to the input
voltage minus the Vdd supply voltage. A 100V Schottky
diode will work for most 72V input telecom applications.
The above equations can be used to calculate power
dissipation in the external diode, however, if the external
diode has significant reverse leakage current, the power
dissipated in that diode due to reverse leakage can be
calculated as:
The on-time is the time the high-side switch is
conducting. In most power supply topologies, the diode
is reverse biased during the switching cycle off-time.
Gate Drive Power Dissipation
Power dissipation in the output driver stage is mainly
caused by charging and discharging the gate to source
and gate to drain capacitance of the external MOSFET.
PWM
Pdiode
Pdiode
where
FF
Q
Q
_
Level
shift
I :
total
REV
Figure 5. Optional Bootstrap Diode
V
fs
D
R
Vdd
REV
=
=
=
external
switching
=
Duty
=
Reverse
diode
Pdiode
I
=
R
Diode
×
Vss
Cycle
V
REV
fwd
current
HB
frequency
Reverse
=
×
+
t
HO
C
ON
1 (
HS
LO
Pdiode
B
−
flow
/
D
f
S
Voltage
)
of
at
RR
the
V
REV
M9999-112806
power
Vin
The reverse
An external
and
MIC4102
supply
T
J