Micrel, Inc.
MIC4223/MIC4224/MIC4225
Functional Description
The MIC4223, MIC4224 and MIC4225 are a family of dual
high speed, high current drivers. The drivers come in both
inverting and non-inverting versions. Each driver has an
enable pin that turns the output off (low) regardless of the
input.
The MIC4223 is a dual inverting driver. The MIC4224 is a
dual non-inverting driver and the MIC4225 contains an
inverting and non-inverting driver.
Enable
Each output has an independent enable pin that forces the
output low when the enable pin is driven low. Each enable
pin is internally pulled-up to V
DD
. The outputs are enabled
by default if the enable pin is left open. Pulling the enable
pin low, below its threshold voltage, forces the output low.
A fast propagation delay between the enable and output
pins quickly disables the output, which is a requirement
during a system fault condition.
Input Stage
The driver input stage is high impedance, TTL-compatible
input stage. The driver’s input threshold voltage makes it
compatible with TTL and CMOS devices that are powered
from supply voltages between 3V and V
DD
. Hysteresis on
the input pin improves noise immunity and prevents input
signals with slow rise times from falsely triggering the
output. The VDD pin current is slightly higher when the
input voltage is above the high level threshold. See the
Typical Characteristic graphs for additional information.
The input voltage signal may go up to -5V below ground
without damage to the driver or cause a latch up condition.
Negative input voltages that are 0.7V below ground or
greater will increase propagation delay.
Output Driver Section
A functional diagram of the driver output is shown in Figure
2. The output drive is a parallel combination of MOSFET
and Bipolar transistor. For a given silicon area, a bipolar
device has a lower on-resistance than an equivalent MOS
device. It sources and sinks current more consistently as
the voltage across it changes. The low drive impedance of
the bipolar allows fast turn-on and turn-off of the external
MOSFET. The driver’s internal MOSFET gives the output
near rail-to-rail drive capability. This ensures a low R
DSON
for the external MOSFET as well as noise immunity from
dv/dt induced glitching.
Figure 2. Output Driver
The slew rate of the output is non-adjustable and depends
only on the V
DD
voltage and how much capacitance is
present at the OUTA, B pin. Changing the slew rate at the
driver’s input pin will not affect the output rise or fall times.
The slew rate at the MOSFET gate can be adjusted by
adding a resistor between the MOSFET gate and the
driver output.
June 2009
9
M9999-061109-A
(408) 944-0800
MICREL [ MICREL SEMICONDUCTOR ]
