MIC4421A MICREL [Micrel Semiconductor], MIC4421A Datasheet - Page 10

• Manufacturer Part Number: MIC4421A
• Description: 9A Peak Low-Side MOSFET Driver Bipolar/CMOS/DMOS Process
• Manufacturer: MICREL [Micrel Semiconductor]

Conditions:
1.
2.
3.
Capacitive Load Power Dissipation
Dissipation caused by a capacitive load is simply the
energy placed in, or removed from, the load capacitance
by the driver. The energy stored in a capacitor is
described by the equation:
As this energy is lost in the driver each time the load is
charged or discharged, for power dissipation calculations
the 1/2 is removed. This equation also shows that it is
good practice not to place more voltage in the capacitor
than is necessary, as dissipation increases as the
square of the voltage applied to the capacitor. For a
driver with a capacitive load:
where:
Inductive Load Power Dissipation
For inductive loads the situation is more complicated.
For the part of the cycle in which the driver is actively
forcing current into the inductor, the situation is the same
as it is in the resistive case:
However, in this instance the R
the on-resistance of the driver when its output is in the
high state, or its on-resistance when the driver is in the
low state, depending on how the inductor is connected,
and this is still only half the story. For the part of the
cycle when the inductor is forcing current through the
driver, dissipation is best described as:
where V
driver (generally around 0.7V). The two parts of the load
dissipation must be summed in to produce P
Micrel, Inc.
June 2007
Table 1. MIC4421A Maximum Operating Frequency
θ
T
C
JA
A
L
= 25°C
= 10,000pF
= 150°C/W
E = 1/2 C V
PL = f C (VS)2
f =
C =
VS =
P
P
P
D
L1
L2
L
is the forward drop of the clamp diode in the
= P
= I
= I V
18V
15V
10V
5V
V
S
2
L1
R
Operating Frequency
Load Capacitance
Driver Supply Voltage
D
+ P
O
(1 – D)
D
2
L2
O
required may be either
Max Frequency
220kHz
300kHz
640kHz
2MHz
L
:
10
Quiescent Power Dissipation
Quiescent power dissipation (PQ, as described in the
input section) depends on whether the input is high or
low. A low input will result in a maximum current drain
(per driver) of ≤0.2mA; a logic high will result in a current
drain of ≤3.0mA.
Quiescent power can therefore be found from:
where:
Transition Power Dissipation
Transition power is dissipated in the driver each time its
output changes state, because during the transition, for
a very brief interval, both the N- and P-Channel
MOSFETs
simultaneously, and a current is conducted through them
from V
approximately:
where (A•s) is a time-current factor derived from the
typical characteristic curve “Crossover Energy vs.
Supply Voltage.”
Total power (P
Definitions
C
D =
f =
I
I
I
P
P
P
H
L
D
D
L
Q
L
=
=
=
=
S
=
=
=
P
I
I
D =
V
P
P
H
L
to ground. The transition power dissipation is
Q
S
T
D
=
=
=
= 2 f V
= V
= P
Duty Cycle expressed as the fraction of time
the input to the driver is high.
Operating Frequency of the driver in Hertz.
Power supply current drawn by a driver
when both inputs are high and neither output
is loaded.
Power supply current drawn by a driver
when both inputs are low and neither output
is loaded.
Output current from a driver in Amps.
Total power dissipated in a driver in Watts.
Power dissipated in the driver due to the
driver’s load in Watts.
Power dissipated in a quiescent driver in
Watts.
Load Capacitance in Farads.
in
D
L
S
) then, as previously described is just:
Quiescent current with input high
Power supply voltage
+ P
Quiescent current with input low
Fraction of time input is high (duty cycle)
[D I
S
the
(A•s)
Q
H
+ P
+ (1 – D) I
output
T
L
]
totem-pole
MIC4421A/4422A
M9999-062707
are
ON