MIC4421 Micrel Semiconductor, MIC4421 Datasheet - Page 7

• Manufacturer Part Number: MIC4421
• Description: 9A-Peak Low-Side MOSFET Driver Bipolar/CMOS/DMOS Process
• Manufacturer: Micrel Semiconductor

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.
CONTROL 180 TO 360
CONDUCTION ANGLE
CONTROL 0 TO 180
CONDUCTION ANGLE
Ø 1 DRIVE SIGNAL
0.1µF
50V
0.1µF
WIMA
MKS 2
2
+15
MIC4421
1
4
Figure 3. Direct Motor Drive
8
5
DRIVE
LOGIC
+
(x2) 1N4448
6, 7
1µF
50V
MKS 2
UNITED CHEMCON SXE
MIC4451
MIC4452
5.6 k
560
V S
V S
1µF
1µF
560µF 50V
DRIVER USING MIC4420/4429
PHASE 1 of 3 PHASE MOTOR
Ø 1
Figure 4. Self Contained Voltage Doubler
+
100µF 50V
Ø 2
M
BYV 10 (x 2)
V S
V S
Ø 3
+
5-48
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 1 F
low ESR film capacitor in parallel with two 0.1 F low ESR
ceramic capacitors, (such as AVX RAM Guard
adequate bypassing. Connect one ceramic capacitor di-
rectly 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 switch-
ing speed. Feedback is especially noticeable with slow-rise
time inputs. The MIC4421 input structure includes about
200mV of hysteresis to ensure clean transitions and free-
dom from oscillation, but attention to layout is still recom-
mended.
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 0.05 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.
Connecting 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.
30
29
28
27
26
25
0
OUTPUT VOLTAGE vs LOAD CURRENT
50
100 150 200 250 300 350
mA
12
LINE
®
), provides
April 1998
Micrel