MIC5013BM datasheet(7/16 Pages) MICREL

7 / 16 page

July 2000

MIC5013

Micrel

Applications Information (Continued)

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

IRF540

10µF

10k

Ω

10m

Ω

IRC 4LPW-5

Figure 2. Low-Side Driver with

Current Shunt

LOAD

Control Input

=7 to 15V

(International Resistive Company)

LOAD

I =20A (trip current)

TRIP

= 200mV

For this example:

2200

–1000

TRIP

R =

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

=24V

IRF541

10µF

100

Ω

20k

Ω

24k

Ω

18m

Ω

IRC 4LPW-5*

Figure 3. High-Side Driver

with Current Shunt

LOAD

Control Input

*International Resistive Company

R1=

R2=100

Ω

R =

1mA

100mV+

2200

–1000

For this example:

I =10A (trip current)

=100mV

TRIP

Circuit Topologies

The MIC5013 is suited for use in high- or low-side driver

applications with over-current protection for both current-

sensing and standard MOSFETs. In addition, the MIC5013

works well in applications where, for faster switching times,

the supply is bootstrapped from the MOSFET source out-

put. Low voltage, high-side drivers (such as shown in the

Test Circuit) are the slowest; their speed is reflected in the

gate turn-on time specifications. The fastest drivers are the

low-side and bootstrapped high-side types. Load current

switching times are often much faster than the time to full

gate enhancement, depending on the circuit type, the

MOSFET, and the load. Turn-off times are essentially the

same for all circuits (less than 10

µs to V

GS = 1V). The choice

of one topology over another is based on a combination of

considerations including speed, voltage, and desired sys-

tem characteristics. Each topology is described in this

section. Note that I

L, as used in the design equations, is the

load current that just trips the over-current comparator.

Low-Side Driver with Current Shunt (Figure 2). The over-

current comparator monitors RS and trips if I

L × RS exceeds

TRIP. R is selected to produce the desired trip voltage.

As a guideline, keep V

TRIP within the limits of 100mV and

500mV (R

TH = 3.3kΩ to 20kΩ). Thresholds at the high end

offer the best noise immunity, but also compromise switch

drop (especially in low voltage applications) and power

dissipation.

The trip current is set higher than the maximum expected

load current—typically twice that value. Trip point accuracy

is a function of resistor tolerances, comparator offset (only

a few millivolts), and threshold bias voltage (V2). The values

shown in Figure 2 are designed for a trip current of 20

amperes. It is important to ground pin 4 at the current shunt

S, to eliminate the effects of ground resistance.

A key advantage of the low-side topology is that the load

supply is limited only by the MOSFET BVDSS rating.

Clamping may be required to protect the MOSFET drain

terminal from inductive switching transients. The MIC5013

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