MIC5018 Datasheet, PDF (7/7 Pages) Micrel Semiconductor – IttyBitty™ High-Side MOSFET Driver Preliminary Information

MIC5018
A gate-to-source zener may also be required when the
maximum gate-to-source voltage could be exceeded due to
normal part-to-part variation in gate output voltage. Other
conditions can momentarily increase the gate-to-source volt-
age, such as turning on a capacitive load or shorting a load.
Inductive Loads
Inductive loads include relays, and solenoids. Long leads
may also have enough inductance to cause adverse effects
in some circuits.
+2.7V to +9V
Micrel
Split Power Supply
Refer to figure 6. The MIC5018 can be used to control a 12V
load by separating the driver supply from the load supply.
+5V
+12V
4.7µF
Logic
High
MIC5018
2
VS
G ^{3 15V}
4 _{CTL GND} 1 _3V
Voltages are approximate
* International Rectifier
logic-level MOSFET
12V
IRLZ44* approx. 0V
To demonstrate
this circuit, try a
40Ω, 5W or
100Ω, 2W
load resistor.
4.7µF
On
Off
MIC5018
2 _VS
G³
4 _{CTL GND} 1
Schottky
Diode
Figure 6. 12V High-Side Switch
A logic-level MOSFET is required. The MOSFET’s maximum
current is limited slightly because the gate is not fully en-
hanced. To predict the MOSFETs performance for any pair
of supply voltages, calculate the gate-to-source voltage and
refer to the MOSFET data sheet.
Figure 5. Switching an Inductive Load
Switching off an inductive load in a high-side application
momentarily forces the MOSFET source negative (as the
V_GS = V_G – (V_{LOAD SUPPLY} – V_DS)
V_G is determined from the driver supply voltage using the
“Typical Characteristics: Gate Output Voltage vs. Supply
Voltage” graph.
inductor opposes changes to current). This voltage spike can ^{Low-Side Switch Configuration}
be very large and can exceed a MOSFET’s gate-to-source _{The low-side configuration makes it possible to switch a}
and drain-to-source ratings. A Schottky diode across the _{voltage much higher than the MIC5018’s maximum supply}
inductive load provides a discharge current path to minimize _voltage.
the voltage spike. The peak current rating of the diode should
+80V
5
be greater than the load current.
* International Rectifier
standard MOSFET
In a low-side application, switching off an inductive load will
BVDSS = 100V
To demonstrate
this circuit, try
momentarily force the MOSFET drain higher than the supply
+2.7 to +9V
1k, 10W or
33k, 1/4W
load resistors.
voltage. The same precaution applies.
4.7µF
MIC5018
2 _VS
G³
IRF540*
N-channel
4 _{CTL GND} 1
MOSFET
On
Off
Figure 7. Low-Side Switch Configuration
The maximum switched voltage is limited only by the
MOSFET’s maximum drain-to-source ratings.
1997
5-161