MIC4414 Datasheet, PDF (9/14 Pages) Micrel Semiconductor – 1.5A, 4.5V to 18V Low-Side MOSFET Driver

Micrel, Inc.
Application Information
The MIC4414 and MIC4415 are designed to provide
high peak current for charging and discharging
capacitive loads. The 1.5A peak value is a nominal value
determined under specific conditions. This nominal value
is used to compare its relative size to other low-side
MOSFET drivers. The MIC4414 and MIC4415 are not
designed to directly switch 1.5A continuous loads.
Supply Bypass
A capacitor from VDD to GND is recommended to
control switching and supply transients. Load current
and supply lead length are some of the factors that affect
capacitor size requirements.
4.7µF or 10µF ceramic or tantalum capacitor is suitable
for many applications. Low-ESR (equivalent series
resistance) metalized film capacitors may also be
suitable. An additional 0.1µF ceramic capacitor is
suggested in parallel with the larger capacitor to control
high-frequency transients. The low ESR (equivalent
series resistance) of ceramic and tantalum capacitors
makes them especially effective, but also makes them
susceptible to uncontrolled inrush current from low
impedance voltage sources (such as NiCd batteries or
automatic test equipment). Avoid instantaneously
applying voltage, capable of very high peak current,
directly to or near low ESR capacitors without additional
current limiting. Normal power supply turn-on (slow rise
time) or printed circuit trace resistance is usually
adequate.
Circuit Layout
Avoid long power supply and ground traces. They exhibit
inductance that can cause voltage transients (inductive
kick). Even with resistive loads, inductive transients can
sometimes exceed the ratings of the MOSFET and the
driver. When a load is switched off, supply lead
inductance forces current to continue flowing and results
in a positive voltage spike. Inductance in the ground
(return) lead to the supply has similar effects, except the
voltage spike is negative. Switching transitions
momentarily draw current from VDD to GND. This
combines with supply lead inductance to create voltage
transients at turn on and turnoff. Transients can also
result in slower apparent rise or fall times when driver’s
ground shifts with respect to the control input.
Minimize the length of supply and ground traces or use
ground and power planes when possible. Bypass
capacitors should be placed as close as practical to the
driver.
MIC4414/MIC4415
MOSFET Selection
Standard MOSFET
A standard N-channel power MOSFET is fully enhanced
with a gate-to-source voltage of approximately 10V and
has an absolute maximum gate-to-source voltage of
±20V. The MIC4414/15’s on-state output is
approximately equal to the supply voltage. The lowest
usable voltage depends upon the behavior of the
MOSFET.
Figure 1. Using a Standard MOSFET
Logic-Level MOSFET
Logic-level N-channel power MOSFETs are fully
enhanced with a gate-to-source voltage of approximately
5V and some of them have an absolute maximum gate-
to-source voltage of ±10V. They are less common and
generally more expensive. The MIC4414/15 can drive a
logic-level MOSFET if the supply voltage, including
transients, does not exceed the maximum MOSFET
gate-to-source rating (10V).
Figure 2. Using a Logic-Level MOSFET
August 2012
9
M9999-080112-A