mic4422a Micrel Semiconductor, mic4422a Datasheet - Page 8
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mic4422a
Manufacturer Part Number
mic4422a
Description
Mic4421a/mic4422a 9a Peak Low-side Mosfet Driver
Manufacturer
Micrel Semiconductor
Datasheet
1.MIC4422A.pdf
(13 pages)
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Control 180°C to 360°C
Application 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 MIC4421A/4422A 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.
V
Micrel, Inc.
June 2007
Control 0°C to 180°C
IN
+15V
Conduction Angle
Conduction Angle
0.1µF
Ø 1 Drive Signal
50V
0.1µF
WIMA
MKS2
Figure 5. Direct Motor Drive
Drive
Logic
MIC4422A
V
V
S
S
MIC4421A
MIC4422A
United Chemcon SXE
1N4448
(x2)
1µF
WIMA
MKS2
Phase 1 of 3 Phase Motor
Driver Using MIC4421A/22A
1µF
1µF
Ø 1
Figure 6. Self Contained Voltage Doubler
Ø 2
500µF
50V
Ø 3
V
V
S
S
BYV 10
(x2)
8
100µF
50V
To guarantee low supply impedance over a wide
frequency range, a parallel capacitor combination is
recommended for supply bypassing. Low inductance
ceramic disk capacitor swith 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
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 MIC4421A/4422A
demands careful PC board layout for best performance.
Since the MIC4421A 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 MIC4421A
input structure includes about 600mV of hysteresis to
ensure clean transitions and freedom from oscillation,
but attention to layout is still recommended.
Figure 7 shows the feedback effect in detail. As the
MIC4421A 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 MIC4421A
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 MIC4421A
GND pins will ensure full logic drive to the input and
ensure fast output switching. Both of the MIC4421A
GND pins should, however, still be connected to power
ground.
30
29
28
27
26
25
0
vs. Load Current
50 100 150 200 250 300 350
Output Voltage
®
mA
), provides adequate
MIC4421A/4422A
M9999-062707