MIC5018 datasheet(10/20 Pages) MICROCHIP

10 / 20 page

MIC5018

DS20006631A-page 10



2021 Microchip Technology Inc. and its subsidiaries

4.4

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.

FIGURE 4-3:

Using a Logic-Level

MOSFET.

Refer to Figure 4-3 for an example showing nominal

voltages. The maximum gate-to-source voltage rating

of a logic-level MOSFET can be exceeded if a higher

supply voltage is used. An external Zener diode can

clamp the gate-to-source voltage as shown in

Figure 4-4. The Zener voltage, plus its tolerance, must

not exceed the absolute maximum gate voltage of the

MOSFET.

FIGURE 4-4:

Gate-to-Source Protection.

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 voltage, such as turning on a capacitive

load or shorting a load.

4.5

Inductive Loads

Inductive loads include relays, and solenoids. Long

leads may also have enough inductance to cause

adverse effects in some circuits.

FIGURE 4-5:

Switching an Inductive

Load.

Switching off an inductive load in a high-side

application momentarily forces the MOSFET source

negative (as the inductor opposes changes to current).

This voltage spike can be very large and can exceed a

MOSFET’s gate-to-source and drain-to-source ratings.

A Schottky diode across the inductive load provides a

discharge current path to minimize the voltage spike.

The peak current rating of the diode should be greater

than the load current.

In a low-side application, switching off an inductive load

will momentarily force the MOSFET drain higher than

the supply voltage. The same precaution applies.

4.6

Split Power Supply

Refer to Figure 4-6. The MIC5018 can be used to

control a 12V load by separating the driver supply from

the load supply.

FIGURE 4-6:

12V High-Side Switch.

A logic-level MOSFET is required. The MOSFET’s

maximum current is limited slightly because the gate is

not fully enhanced. To predict the MOSFET’s

performance for any pair of supply voltages, calculate

the gate-to-source voltage and refer to the MOSFET

data sheet.

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