MIC4422YN Datasheet, PDF (7/12 Pages) Micrel Semiconductor – 9A-Peak Low-Side MOSFET Driver

MIC4421/4422
Applications Information
Supply Bypassing
Charging and discharging large capacitive loads quickly
requires large currents. For example, charging a 10,000pF
load to 18V in 50ns requires 3.6A.
The MIC4421/4422 has double bonding on the supply pins,
the ground pins and output pins. This reduces parasitic
lead inductance. Low inductance enables large currents to
be switched rapidly. It also reduces internal ringing that can
cause voltage breakdown when the driver is operated at or
near the maximum rated voltage.
Internal ringing can also cause output oscillation due to
feedback. This feedback is added to the input signal since it
is referenced to the same ground.
Ø1 DRIV E S IGNA L
CONDUCTION ANGLE
CONTROL 0° TO 180°
CONDUCTION ANGLE
CONTROL 180° TO 360°
VS
1µF
MIC4451
VS
DRIVE
LOGIC
Ø1
VS
1µF
MIC4452
Ø2
M
Ø3
VS
PHASE 1 of 3 PHASE MOTOR
DRIVER USING MIC4420/4429
Micrel, Inc.
To guarantee low supply impedance over a wide frequency
range, a parallel capacitor combination is recommended for
supply bypassing. Low inductance ceramic disk capacitors
with short lead lengths (< 0.5 inch) should be used. A 1µF low
ESR film capacitor in parallel with two 0.1µF low ESR ceramic
capacitors, (such as AVX RAM Guard^®), provides adequate
bypassing. Connect one ceramic capacitor directly between
pins 1 and 4. Connect the second ceramic capacitor directly
between pins 8 and 5.
Grounding
The high current capability of the MIC4421/4422 demands
careful PC board layout for best performance. Since the
MIC4421 is an inverting driver, any ground lead impedance
will appear as negative feedback which can degrade switching
speed. Feedback is especially noticeable with slow-rise time
inputs. The MIC4421 input structure includes about 200mV
of hysteresis to ensure clean transitions and freedom from
oscillation, but attention to layout is still recommended.
Figure 5 shows the feedback effect in detail. As the MIC4421
input begins to go positive, the output goes negative and
several amperes of current flow in the ground lead. As little
as 0.05Ω of PC trace resistance can produce hundreds of
millivolts at the MIC4421 ground pins. If the driving logic is
referenced to power ground, the effective logic input level is
reduced and oscillation may result.
To insure optimum performance, separate ground traces
should be provided for the logic and power connections. Con-
necting the logic ground directly to the MIC4421 GND pins
will ensure full logic drive to the input and ensure fast output
switching. Both of the MIC4421 GND pins should, however,
still be connected to power ground.
Figure 3. Direct Motor Drive
+15
(x2) 1N4448
5.6 kΩ
560 Ω
0.1µF
50V
2
0.1µF
WIMA
MKS2
+ _1µF
50V
1
MKS2
8 _{6, 7}
MIC4421
BYV 10 (x 2)
+
5
4
560µF 50V
+
100µF 50V
UNITED CHEMCON SXE
OUTPUT VOLTAGE vs LOAD CURRENT
30
29
28
12 Ω LINE
27
26
25
0
50 100 150 200 250 300 350
mA
Figure 4. Self Contained Voltage Doubler
August 2005
7
M9999-081005