MIC5019 Datasheet, PDF (7/12 Pages) Micrel Semiconductor – Ultra-Small High-Side N-Channel MOSFET Driver with Integrated Charge Pump

Micrel, Inc.
Application Information
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.
A 4.7μF or 10μF ceramic capacitor, aluminum
electrolytic or tantalum capacitor is suitable for many
applications.
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 applying voltage instantaneously,
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 MIC5019 is designed to drive N-channel
enhancement type MOSFETs. The gate output (OUT) of
the MIC5019 provides a voltage, referenced to ground,
that is greater than the supply voltage. Refer to the
“Typical Characteristics: 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_OUT – (V_SUPPLY – V_DS)
where:
V_GS = gate-to-source voltage (enhancement)
V_OUT = OUT voltage (from graph “OUT Voltage vs
Supply Voltage)
V_DD = supply voltage
V_DS = drain-to-source voltage
(approx. 0V at low current, or when fully enhanced)
MIC5019
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.
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 4.5V supply, the
MIC5019 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.
Figure 2. Using a Standard MOSFET
The MIC5019 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. Some of
the MOSFET’s may have an absolute maximum gate-to-
source voltage of ±10V (Refer to MOSFET datasheet).
Figure 1. Node Voltages
July 2012
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