MIC5021 datasheet(11/24 Pages) MICROCHIP

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DS20005677B-page 11

MIC5021

6.0

APPLICATION INFORMATION

The MIC5021 MOSFET driver is intended for high-side

switching applications where overcurrent limiting and

high speed are required. The MIC5021 can control

MOSFETs that switch voltages up to 36V.

6.1

High-Side Switch Circuit

Advantages

High-side switching allows more of the load related

components and wiring to remain near ground potential

when compared to low-side switching. This reduces the

chances of short-to-ground accidents or failures.

6.2

Speed Advantage

The MIC5021 is about two orders of magnitude faster

than the low cost MIC5014 making it suitable for

high-frequency high-efficiency circuit operation in PWM

(pulse width modulation) designs used for motor con-

trol, SMPS (switch-mode power supply) and heating

element control.

Switched loads (on/off) benefit from the MIC5021’s fast

switching times by allowing use of MOSFETs with

smaller safe operating areas. Larger MOSFETs are

often required when using slower drivers.

6.3

Supply Voltage

The MIC5021’s supply input (VDD) is rated up to 36V.

The supply voltage must be equal to or greater than the

voltage applied to the drain of the external N-channel

MOSFET.

A 16V minimum supply is recommended to produce

continuous on-state, gate drive voltage for standard

MOSFETs (10V nominal gate enhancement).

When the driver is powered from a 12V to 16V supply,

a logic-level MOSFET is recommended (5V nominal

gate enhancement).

PWM operation may produce satisfactory gate

enhancement at lower supply voltages. This occurs

when fast switching repetition makes the boost capac-

itor a more significant voltage supply than the internal

charge pump.

6.4

Logic-Level MOSFET Precautions

Logic-level

MOSFETs

have

lower

maximum

gate-to-source voltage ratings (typically ±10V) than

standard MOSFETs (typically ±20V). When an external

MOSFET is turned on, the doubling effect of the boost

capacitor can cause the gate-to-source voltage to

momentarily exceed 10V. Internal zener diodes clamp

this voltage to 16V maximum which is too high for

logic-level MOSFETs. To protect logic-level MOSFETs,

connect a zener diode (5V ≤ VZENER < 10V) from gate

to source.

6.5

Overcurrent Limiting

A 50 mV comparator is provided for current sensing.

The low level trip point minimizes I2R losses when a

power resistor is used for current sensing.

The adjustable retry feature can be used to handle

loads with high initial currents, such as lamps or heat-

ing elements, and can be adjusted from the CT connec-

tion.

CT to ground maintains gate drive shutdown following

an overcurrent condition.

CT open, or a capacitor to ground, causes automatic

retry. The default duty cycle (CT open) is approximately

20%. Refer to the Electrical Characteristics when

selecting a capacitor for reduced duty cycle.

CT through a pull-up resistor to VDD increases the duty

cycle. Increasing the duty cycle increases the power

dissipation in the load and MOSFET under a fault con-

dition. Circuits may become unstable at a duty cycle of

about 75% or higher, depending on conditions. Cau-

tion: The MIC5021 may be damaged if the voltage

applied to CT exceeds the absolute maximum voltage

rating.

6.6

Boost Capacitor Selection

The boost capacitor value will vary depending on the

supply voltage range.

A 0.01 µF boost capacitor is recommended for best

performance in the 12V to 20V range. (See Figure 6-1.)

Larger capacitors may damage the MIC5021.

FIGURE 6-1:

12V to 20V Configuration.

If the full 12V to 36V voltage range is required, the

boost capacitor value must be reduced to 2.7 nF

(Figure 6-2). The recommended configuration for the

20V to 36V range is to place the capacitor is placed

between VDD and VBOOST as shown in Figure 6-3.

V DD

Input

C T

Gnd

V BOOST

Gate

Sense-

Sense+

TTL Input

+12V to +20V

MIC5021

10μF

0.01

μF

Load

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