MIC5018_06 Datasheet, PDF (6/8 Pages) Micrel Semiconductor – IttyBitty™ High-Side MOSFET Driver

Micrel, Inc.
Application Information
Supply Bypass
A capacitor from VS 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.
A 4.7µF or 10µF aluminum electrolytic or tantalum
capacitor is suitable for many applications.
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 automatic test equipment). Avoid
instantaneously applying voltage, capable of high peak
current, directly to or near tantalum capacitors without
additional current limiting. Normal power supply turn-on
(slow rise time) or printed circuit trace resistance is
usually adequate for normal product usage.
MOSFET Selection
The MIC5018 is designed to drive N-channel
enhancement type MOSFETs. The gate output (G) of
the MIC5018 provides a voltage, referenced to ground,
that is greater than the supply voltage. Refer to the
“Typical Characteristics: Gate Output Voltage vs. Supply
Voltage” graph.
The supply voltage and the MOSFET drain-to-source
voltage drop determine the gate-to-source voltage.
V_GS = V_G – (V_SUPPLY – V_DS)
where:
V_GS = gate-to-source voltage (enhancement)
V_G = gate voltage (from graph)
V_SUPPLY = supply voltage
V_DS = drain-to-source voltage
(approx. 0V at low current, or when fully enhanced)
V_{S U P P L Y}
MIC5018
2 _VS
G ^{3 VG G}
4 _{C T L GND} 1 _{VG S}
D
V_{D S}
S
V_{L O A D}
Figure 1. Voltages
The performance of the MOSFET is determined by the
gate-to-source voltage. Choose the type of MOSFET
according to the calculated gate-to-source voltage.
April 2006
MIC5018
Standard MOSFET
Standard MOSFETs are fully enhanced with a gate-to-
source voltage of about 10V. Their absolute maximum
gate-to-source voltage is ±20V.
With a 5V supply, the MIC5018 produces a gate output
of approximately 15V. Figure 2 shows how the remaining
voltages conform. The actual drain-to-source voltage
drop across an IRFZ24 is less than 0.1V with a 1A load
and 10V enhancement. Higher current increases the
drain-to-source voltage drop, increasing the gate-to-
source voltage.
+5V
4.7µF
Logic
High
MIC5018
2 _VS
G ^{3 15V}
4 _{CTL GND} 1 _10V
Voltages are approximate _{5 V}
* International Rectifier
standard MOSFET
IRFZ24* approx. 0V
To demonstrate
this circuit, trya
2 , 20W
load resistor.
Figure 2. Using a Standard MOSFET
The MIC5018 has an internal zener diode that limits the
gate-to-ground voltage to approximately 16V.
Lower supply voltages, such as 3.3V, produce lower
gate output voltages which will not fully enhance
standard MOSFETs. This significantly reduces the
maximum current that can be switched. Always refer to
the MOSFET data sheet to predict the MOSFET’s
performance in specific applications.
Logic-Level MOSFET
Logic-level N-channel MOSFETs are fully enhanced with
a gate-to-source voltage of approximately 5V and
generally have an absolute maximum gate-to-source
voltage of ±10V.
+3.3V
4.7µF
Logic
High
MIC5018
2 _VS
G ^{3 9V}
4 _{CTL GND} 1 _5.7V
Voltages are approximate
* International Rectifier
logic-level MOSFET
3.3V
IRLZ44* approx. 0V
To demonstrate
this circuit, try
5 , 5W or
47 , 1/4W
load resistors.
Figure 3. Using a Logic-Level MOSFET
Refer to Figure 3 for an example showing nominal
voltages. The maximum gate-to-source voltage rating of
a logic-level MOSFET can be exceeded if a higher
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M9999-042406
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