MIC4416 Datasheet, PDF (8/9 Pages) Micrel Semiconductor – IttyBitty™ Low-Side MOSFET Driver

MIC4416
Application Information
The MIC4416/7 is designed to provide high peak current for
charging and discharging capacitive loads. The 1.2A peak
value is a nominal value determined under specific condi-
tions. This nominal value is used to compare its relative size
to other low-side MOSFET drivers. The MIC4416/7 is not
designed to directly switch 1.2A continuous loads.
Supply Bypass
Capacitors from VS to GND are recommended to control
switching and supply transients. Load current and supply
lead length are some of the factors that affect capacitor
size requirements.
A 4.7µF or 10µF tantalum capacitor is suitable for many
applications. Low-ESR (equivalent series resistance) metal-
ized 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 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 auto-
matic test equipment). Avoid instantaneously applying volt-
age, capable of very high peak current, directly to or near
tantalum capacitors without additional current limiting. Nor-
mal power supply turn-on (slow rise time) or printed circuit
trace resistance is usually adequate for normal product
usage.
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—resulting 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 VS 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.
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 MIC4416/7’s on-state output is approximately equal to
the supply voltage. The lowest usable voltage depends upon
the behavior of the MOSFET.
+15V
* Gate enhancement voltage
+8V to +18V
4.7µF
Try a
15Ω, 15W
or
1k, 1/4W
resistor
0.1µF
MIC4416
3
VS
2
G
Logic
Input
4 _{CTL GND} 1
† _{International Rectifier}
100mΩ, 60V MOSFET
V_GS*
Standard
MOSFET
IRFZ24^†
Micrel
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 have
an absolute maximum gate-to-source voltage of ±10V. They
are less common and generally more expensive.
The MIC4416/7 can drive a logic-level MOSFET if the supply
voltage, including transients, does not exceed the maximum
MOSFET gate-to-source rating (10V).
* Gate enhancement voltage
(must not exceed 10V)
+4.5V to 10V*
4.7µF
+5V
Try a
3Ω, 10W
or
100Ω, 1/4W
resistor
0.1µF
Logic
Input
MIC4416
3 _VS
G²
4 _{CTL GND} 1
V_GS*
Logic-Level
MOSFET
IRLZ44^†
† _{International Rectifier}
28mΩ, 60V MOSFET
Figure 2. Using a Logic-Level MOSFET
At low voltages, the MIC4416/7’s internal P- and N-channel
MOSFET’s on-resistance will increase and slow the output
rise time. Refer to “Typical Characteristics” graphs.
Inductive Loads
V_SWITCHED
V_SUPPLY
4.7µF
Schottky
Diode
0.1µF
On
Off
MIC4416
3 _VS
G²
4 _{CTL GND} 1
Figure 3. Switching an Inductive Load
Switching off an inductive load in a low-side application forces
the MOSFET drain higher than the supply voltage (as the
inductor resists changes to current). To prevent exceeding
the MOSFET’s drain-to-gate and drain-to-source ratings, a
Schottky diode should be connected across the inductive
load.
5-30
April 1998