MIC4420 Micrel Semiconductor, MIC4420 Datasheet - Page 8

• Manufacturer Part Number: MIC4420
• Description: 6A-Peak Low-Side MOSFET Driver Bipolar/CMOS/DMOS Process
• Manufacturer: Micrel Semiconductor

MIC4420/4429
Input Stage
The input voltage level of the 4429 changes the quiescent
supply current. The N channel MOSFET input stage tran-
sistor drives a 450 A current source load. With a logic “1”
input, the maximum quiescent supply current is 450 A.
Logic “0” input level signals reduce quiescent current to
55 A maximum.
The MIC4420/4429 input is designed to provide 300mV of
hysteresis. This provides clean transitions, reduces noise
sensitivity, and minimizes output stage current spiking
when changing states. Input voltage threshold level is
approximately 1.5V, making the device TTL compatible
over the 4 .5V to 18V operating supply voltage range. Input
current is less than 10 A over this range.
The MIC4429 can be directly driven by the TL494, SG1526/
1527, SG1524, TSC170, MIC38HC42 and similar switch
mode power supply integrated circuits. By offloading the
power-driving duties to the MIC4420/4429, the power sup-
ply controller can operate at lower dissipation. This can
improve performance and reliability.
The input can be greater than the
current will flow into the input lead. The propagation delay
for T
ture. The input currents can be as high as 30mA p-p
(6.4mA
voltage. No damage will occur to MIC4420/4429 however,
and it will not latch.
The input appears as a 7pF capacitance, and does not
change even if the input is driven from an AC source. Care
should be taken so that the input does not go more than 5
volts below the negative rail.
Power Dissipation
CMOS circuits usually permit the user to ignore power
dissipation. Logic families such as 4000 and 74C have
outputs which can only supply a few milliamperes of current,
and even shorting outputs to ground will not force enough
April 1998
Figure 3. Switching Time Degradation Due to
D2
0 V
will increase to as much as 400ns at room tempera-
RMS
5.0V
0.1µF
) with the input, 6 V greater than the supply
2
+18 V
MIC4429
Negative Feedback
1
4
8
5
6, 7
WIMA
MK22
1 µF
TEK CURRENT
0.1µF
PROBE 6302
+
V
S
supply, however,
10,000 pF
POLYCARBONATE
18 V
0 V
5-39
current to destroy the device. The MIC4420/4429 on the
other hand, can source or sink several amperes and drive
large capacitive loads at high frequency. The package
power dissipation limit can easily be exceeded. Therefore,
some attention should be given to power dissipation when
driving low impedance loads and/or operating at high fre-
quency.
The supply current vs frequency and supply current vs
capacitive load characteristic curves aid in determining
power dissipation calculations. Table 1 lists the maximum
safe operating frequency for several power supply voltages
when driving a 2500pF load. More accurate power dissipa-
tion figures can be obtained by summing the three dissipa-
tion sources.
Given the power dissipation in the device, and the thermal
resistance of the package, junction operating temperature
for any ambient is easy to calculate. For example, the
thermal resistance of the 8-pin MSOP package, from the
data sheet, is 250 C/W. In a 25 C ambient, then, using a
maximum junction temperature of 150 C, this package will
dissipate 500mW.
Accurate power dissipation numbers can be obtained by
summing the three sources of power dissipation in the
device:
• Load Power Dissipation (P L )
• Quiescent power dissipation (P Q )
• Transition power dissipation (P T )
Calculation of load power dissipation differs depending on
whether the load is capacitive, resistive or inductive.
Resistive Load Power Dissipation
Dissipation caused by a resistive load can be calculated as:
where:
R
Table 1: MIC4429 Maximum
Operating Frequency
Conditions: 1. DIP Package (
D =
O
I =
= the output resistance of the driver when the output is
the current drawn by the load
high, at the power supply voltage used. (See data
sheet)
fraction of time the load is conducting (duty cycle)
P
18V
15V
10V
V
L
2. T
3. C
S
= I
A
L
2
= 25 C
= 2500pF
R
O
D
JA
= 130 C/W)
Max Frequency
1.6MHz
500kHz
700kHz
Micrel
5