July 2000

MIC5013

Micrel

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

=24V

IRCZ44
(S=2590,
R=11m

)

10µF

20k

4.3k

Figure 1. High-Side Driver with

Current-Sensing MOSFET

LOAD

Control Input

R1=

100mV

SRR

(SR+R )

SR( +100mV)

R I

( +100mV)

R =

1000

2200

TRIP

For this example:

=30A (trip current)

=100mV

TRIP

SENSE

SOURCE

KELVIN

MIC5013

Protected High- or Low-Side MOSFET Driver

Final Information

General Description

The MIC5013 is an 8-pin MOSFET driver with over-current
shutdown and a fault flag. It is designed to drive the gate of
an N-channel power MOSFET above the supply rail high-side
power switch applications. The MIC5013 is compatible with
standard or current-sensing power MOSFETs in both high-
and low-side driver topologies.

The MIC5013 charges a 1nF load in 60

s typical and protects

the MOSFET from over-current conditions. The current sense
trip point is fully programmable and a dynamic threshold
allows high in-rush current loads to be started. A fault pin
indicates when the MIC5013 has turned off the FET due to
excessive current.

Other members of the Micrel driver family include the MIC5011
minimum parts count driver and MIC5012 dual driver.

Features

· 7V to 32V operation
· Less than 1

A standby current in the "OFF" state

· Available in small outline SOIC packages
· Internal charge pump to drive the gate of an N-channel

power FET above supply

· Internal zener clamp for gate protection
· 60

s typical turn-on time to 50% gate overdrive

· Programmable over-current sensing
· Dynamic current threshold for high in-rush loads
· Fault output pin indicates current faults
· Implements high- or low-side switches

Applications

· Lamp drivers
· Relay and solenoid drivers
· Heater switching
· Power bus switching
· Motion control

Ordering Information

Part Number

Temperature Range

Package

MIC5013BN

C to +85

8-pin Plastic DIP

MIC5013BM

C to +85

8-pin SOIC

Typical Application

Protected under one or more of the following Micrel patents:

patent #4,951,101; patent #4,914,546

Note: The MIC5013 is ESD sensitive.

Micrel, Inc. · 1849 Fortune Drive · San Jose, CA 95131 · USA · tel + 1 (408) 944-0800 · fax + 1 (408) 944-0970 · http://www.micrel.com

MIC5013

Micrel

MIC5013

July 2000

Pin Description

(Refer to Figures 1 and 2)

Pin Number

Pin Name

Pin Function

Input

Resets current sense latch and turns on power MOSFET when taken above
threshold (3.5V typical). Pin 1 requires <1

A to switch.

Threshold

Sets current sense trip voltage according to:

2200

R +1000

TRIP

where R

to ground is 3.3k to 20k

. Adding capacitor C

increases the

trip voltage at turn-on to 2V. Use C

=10

F for a 10ms turn-on time

constant.

Sense

The sense pin causes the current sense to trip when V

SENSE

is V

TRIP

above

SOURCE

. Pin 3 is used in conjunction with a current shunt in the source of

a 3 lead FET or a resistor R

in the sense lead of a current sensing FET.

Source

Reference for the current sense voltage on pin 3 and return for the gate
clamp zener. Connect to the load side of current shunt or kelvin lead of
current sensing FET. Pins 3 and 4 can safely swing to 10V when turning
off inductive loads.

Ground

Gate

Drives and clamps the gate of the power FET. Pin 6 will be clamped to
approximately 0.7V by an internal diode when turning off inductive loads.

Supply pin; must be decoupled to isolate from large transients caused by
the power FET drain. 10

F is recommended close to pins 7 and 5.

Fault

Outputs status of protection circuit when pin 1 is high. Fault low indicates
normal operation; fault high indicates current sense tripped.

Absolute Maximum Ratings

(Note 1, 2)

Input Voltage, Pin 1

10 to V

Threshold Voltage, Pin 2

0.5 to +5V

Sense Voltage, Pin 3

10V to V

Source Voltage, Pin 4

10V to V

Current into Pin 4

50mA

Gate Voltage, Pin 6

1V to 50V

Supply Voltage (V

), Pin 7

0.5V to 36V

Fault Output Current, Pin 8

1mA to +1mA

Junction Temperature

150

Operating Ratings

(Notes 1, 2)

Power Dissipation

1.25W

(Plastic DIP)

100

C/W

(SOIC)

170

C/W

Ambient Temperature: B version

C to +85

Storage Temperature

C to +150

Lead Temperature

260

(Soldering, 10 seconds)
Supply Voltage (V

), Pin 7

7V to 32V high side

7V to 15V low side

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

Pin Configuration

July 2000

MIC5013

Micrel

Electrical Characteristics

(Note 3, 5) Test circuit. T

= 55

C to +125

C, V

= 15V

, all switches open, unless

otherwise specified.

Parameter

Conditions

Min

Typical

Max

Units

Supply Current, I

= 32V

= 0V, S4 closed

0.1

= V

= 32V

Logic Input Voltage, V

= 4.75V

Adjust V

for V

GATE

low

Adjust V

for V

GATE

high

4.5

=15V

Adjust V

for V

GATE

high

5.0

Logic Input Current, I

V+ = 32V

= 0V

= 32V

Input Capacitance

Pin 1

Gate Drive, V

GATE

S1, S2 closed,

= 7V, I

= 0

= V+, V

= 5V

= 15V, I

= 100

Zener Clamp,

S2 closed, V

= 5V

V+ = 15V, V

= 15V

12.5

GATE

SOURCE

= 32V, V

= 32V

Gate Turn-on Time, t

switched from 0 to 5V; measure time

200

(Note 4)

for V

GATE

to reach 20V

Gate Turn-off Time, t

OFF

switched from 5 to 0V; measure time

for V

GATE

to reach 1V

Threshold Bias Voltage, V

= 200

1.7

2.2

Current Sense Trip Voltage,

S2 closed, V

= 5V,

= 7V,

S4 closed

105

135

SENSE

SOURCE

Increase I

= 100

= 4.9V, S4 open

100

130

= 15V

S4 closed

150

210

270

= 200

= 11.8V, S4 open

140

200

260

= 32V

= 0V, S4 open

360

520

680

= 500

= 25.5V, S4 open

350

500

650

Peak Current Trip Voltage,

S3, S4 closed,

1.6

2.1

SENSE

SOURCE

= 15V, V

= 5V

Fault Output Voltage, V

= 0V, I

= 100

0.4

= 5V, I

= 100

A, current sense tripped

14.6

Note 1.

Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when
operating the device beyond its specified Operating Ratings.

Note 2.

The MIC5010 is ESD sensitive.

Note 3.

Minimum and maximum Electrical Characteristics are 100% tested at T

= 25

C and T

= 85

C, and 100% guaranteed over the entire

range. Typicals are characterized at 25

C and represent the most likely parametric norm.

Note 4.

Test conditions reflect worst case high-side driver performance. Low-side and bootstrapped topologies are significantly faster--see
Applications Information.

Note 5.

Specification for packaged product only.

MIC5013

Micrel

MIC5013

July 2000

Block Diagram

V+

CHARGE

PUMP

V. REG

LOGIC

MIC5013

500

V+

Gate

Sense

Source

Ground

Threshold

Input

Fault

CURRENT

SENSE

LATCH

TRIP

12.5V

Applications Information

Functional Description (refer to block diagram)

The various MIC5013 functions are controlled via a logic
block connected to the input pin 1. When the input is low, all
functions are turned off for low standby current and the gate
of the power MOSFET is also held low through 500

to an

N-channel switch. When the input is taken above the turn-
on threshold (3.5V typical), the N-channel switch turns off
and the charge pump is turned on to charge the gate of the
power FET. A bandgap type voltage regulator is also turned
on which biases the current sense circuitry.

The charge pump incorporates a 100kHz oscillator and on-
chip pump capacitors capable of charging 1nF to 5V above
supply in 60

s typical. The charge pump is capable of

pumping the gate up to over twice the supply voltage. For
this reason, a zener clamp (12.5V typical) is provided
between the gate pin 6 and source pin 4 to prevent exceed-
ing the V

rating of the MOSFET at high supplies.

The current sense operates by comparing the sense volt-
age at pin 3 to an offset version of the source voltage at pin
4. Current I2 flowing in threshold pin 2 is mirrored and
returned to the source via a 1k

resistor to set the offset, or

trip voltage. When (V

SENSE

SOURCE

) exceeds V

TRIP

, the

current sense trips and sets the current sense latch to turn
off the power FET. An integrating comparator is used to
reduce sensitivity to spikes on pin 3. The latch is reset to turn
the FET back on by "recycling" the input pin 1 low and then
high again.

A resistor R

from pin 2 to ground sets I2, and hence V

TRIP

An additional capacitor C

from pin 2 to ground creates a

higher trip voltage at turn-on, which is necessary to prevent
high in-rush current loads such as lamps or capacitors from
false-tripping the current sense.

When the current sense has tripped, the fault pin 8 will be
high as long as the input pin 1 remains high. However, when
the input is low the fault pin will also be low.

Construction Hints

High current pulse circuits demand equipment and assem-
bly techniques that are more stringent than normal low
current lab practices. The following are the sources of
pitfalls most often encountered during prototyping: Sup-
plies: many bench power supplies have poor transient
response. Circuits that are being pulse tested, or those that
operate by pulse-width modulation will produce strange
results when used with a supply that has poor ripple
rejection, or a peaked transient response. Monitor the
power supply voltage that appears at the drain of a high-
side driver (or the supply side of the load in a low-side driver)
with an oscilloscope. It is not uncommon to find bench
power supplies in the 1kW class that overshoot or under-
shoot by as much as 50% when pulse loaded. Not only will
the load current and voltage measurements be affected, but
it is possible to over-stress various components--espe-
cially electrolytic capacitors--with possibly catastrophic
results. A 10

F supply bypass capacitor at the chip is

recommended.

Residual Resistances: Resistances in circuit connections
may also cause confusing results. For example, a circuit
may employ a 50m

power MOSFET for low drop, but

careless construction techniques could easily add 50 to
100m

resistance. Do not use a socket for the MOSFET. If

the MOSFET is a TO-220 type package, make high-current
drain connections to the tab. Wiring losses have a profound
effect on high-current circuits. A floating millivoltmeter can
identify connections that are contributing excess drop un-
der load.

July 2000

MIC5013

Micrel

Applications Information

(Continued)

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

IRF540

10µF

10k

10m

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:

R =

2200

1000

TRIP

R =

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

=24V

IRF541

10µF

100

20k

24k

18m

IRC 4LPW-5*

Figure 3. High-Side Driver

with Current Shunt

LOAD

Control Input

*International Resistive Company

R1=

R2=100

R =

1mA

100mV+

2200

1000

For this example:

I =10A (trip current)

V =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

s to V

= 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

, 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

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

= 3.3k

to 20k

). 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
R

, 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

MIC5013

Micrel

MIC5013

July 2000

Suppliers of Kelvin-sensed power resistors:
Dale Electronics, Inc., 2064 12th Ave., Columbus, NE 68601. Tel: (402) 564-3131
International Resistive Co., P.O. Box 1860, Boone, NC 28607-1860. Tel: (704) 264-8861
Kelvin, 14724 Ventura Blvd., Ste. 1003, Sherman Oaks, CA 91403-3501. Tel: (818) 990-1192
RCD Components, Inc., 520 E. Industrial Pk. Dr., Manchester, NH 03103. Tel: (603) 669-0054
Ultronix, Inc., P.O. Box 1090, Grand Junction, CO 81502. Tel: (303) 242-0810

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

IRCZ44
(S=2590,
R=11m

)

10µF

20k

Figure 4. Low-Side Driver with

Current-Sensing MOSFET

LOAD

Control Input

=15V

LOAD

SOURCE

KELVIN

SENSE

R I

R =

TRIP

R =

1000

2200

TRIP

For this example:

=20A (trip current)

=100mV

TRIP

Applications Information

(Continued)

supply should be limited to 15V in low-side topologies;
otherwise, a large current will be forced through the gate
clamp zener.

Low-side drivers constructed with the MIC501X family are
also fast; the MOSFET gate is driven to near supply
immediately when commanded ON. Typical circuits achieve
10V enhancement in 10

s or less on a 12 to 15V supply.

High-Side Driver with Current Shunt (Figure 3). The
comparator input pins (source and sense) float with the
current sensing resistor (R

) on top of the load. R1 and R2

add a small, additional potential to V

TRIP

to prevent false-

triggering of the over-current shutdown circuit with open or
inductive loads. R1 is sized for a current flow of 1mA, while
R2 contributes a drop of 100mV. The shunt voltage should
be 200 to 500mV at the trip point. The example of Figure 3
gives a 10A trip current when the output is near supply. The
trip point is somewhat reduced when the output is at ground
as the voltage drop across R1 (and therefore R2) is zero.

High-side drivers implemented with MIC5013 drivers are
self-protected against inductive switching transients. Dur-
ing turn-off an inductive load will force the MOSFET source
5V or more below ground, while the driver holds the gate at
ground potential. The MOSFET is forced into conduction,
and it dissipates the energy stored in the load inductance.
The MIC5013 source and sense pins (3 and 4) are designed
to withstand this negative excursion without damage. Exter-
nal clamp diodes are unnecessary.

Current Shunts (R

). Low-valued resistors are necessary

for use at R

.Values for R

range from 5 to 50m

, at 2 to

10W. Worthy of special mention are Kelvin-sensed, "four-
terminal" units supplied by a number of manufacturers

(see next page). Kelvin-sensed resistors eliminate errors

caused by lead and terminal resistances, and simplify
product assembly. 10% tolerance is normally adequate,
and with shunt potentials of 200mV thermocouple effects
are insignificant. Temperature coefficient is important; a
linear, 500 ppm/

C change will contribute as much as 10%

shift in the over-current trip point. Most power resistors
designed for current shunt service drift less than 100 ppm/

Low-Side Driver with Current Sensing MOSFET (Figure
4). Several manufacturers now supply power MOSFETs in
which a small sampling of the total load current is diverted
to a "sense" pin. One additional pin, called "Kelvin source,"
is included to eliminate the effects of resistance in the
source bond wires. Current-sensing MOSFETs are speci-
fied with a sensing ratio "S" which describes the relationship
between the on-resistance of the sense connection and the
body resistance "R" of the main source pin. Current sensing
MOSFETs eliminate the current shunt required by standard
MOSFETs.

The design equations for a low-side driver using a current
sensing MOSFET are shown in Figure 4. "S" is specified on
the MOSFET's datasheet, and "R" must be measured or
estimated. V

TRIP

must be less than R

, or else R

will

become negative. Substituting a MOSFET with higher on-
resistance, or reducing V

TRIP

fixes this problem. V

TRIP

100 to 200mV is suggested. Although the load supply is
limited only by MOSFET ratings, the MIC5013 supply
should be limited to 15V to prevent damage to the gate
clamp zener. Output clamping is necessary for inductive
loads.

"R" is the body resistance of the MOSFET, excluding bond
resistances. R

DS(ON)

as specified on MOSFET data sheets

July 2000

MIC5013

Micrel

Applications Information

(Continued)

includes bond resistances. A Kelvin-connected ohmmeter
(using TAB and SOURCE for forcing, and SENSE and
KELVIN for sensing) is the best method of evaluating "R."
Alternatively, "R" can be estimated for large MOSFETs
(R

DS(ON)

100m

) by simply halving the stated R

DS(ON)

, or

by subtracting 20 to 50m

from the stated R

DS(ON)

for

smaller MOSFETs.

High-Side Driver with Current Sensing MOSFET (Figure
5). The design starts by determining the value of "S" and "R"
for the MOSFET (use the guidelines described for the low-
side version). Let V

TRIP

= 100mV, and calculate R

for a

desired trip current. Next calculate R

and R1. The trip

point is somewhat reduced when the output is at ground as
the voltage drop across R1 is zero. No clamping is required
for inductive loads, but may be added to reduce power
dissipation in the MOSFET.

Typical Applications

Start-up into a Dead Short. If the MIC5013 attempts to turn
on a MOSFET when the load is shorted, a very high current
flows. The over-current shutdown will protect the MOSFET,
but only after a time delay of 5 to 10

s. The MOSFET must

be capable of handling the overload; consult the device's
SOA curve. If a short circuit causes the MOSFET to exceed
its 10

s SOA, a small inductance in series with the source

can help limit di/dt to control the peak current during the 5
to 10

s delay.

When testing short-circuit behavior, use a current probe
rated for both the peak current and the high di/dt.

The over-current shutdown delay varies with comparator
overdrive, owing to noise filtering in the comparator. A delay
of up to 100

s can be observed at the threshold of shut-

down. A 20% overdrive reduces the delay to near minimum.

Incandescent Lamps. The cold filament of an incandes-
cent lamp exhibits less than one-tenth as much resistance
as when the filament is hot. The initial turn-on current of a
#6014 lamp is about 70A, tapering to 4.4A after a few

hundred milliseconds. It is unwise to set the over-current trip
point to 70A to accommodate such a load. A "resistive" short
that draws less than 70A could destroy the MOSFET by
allowing sustained, excessive dissipation. If the over-cur-
rent trip point is set to less than 70A, the MIC5013 will not
start a cold filament. The solution is to start the lamp with a
high trip point, but reduce this to a reasonable value after the
lamp is hot.

The MIC5013 over-current shutdown circuit is designed to
handle this situation by varying the trip point with time (see
Figure 5). R

TH1

functions in the conventional manner,

providing a current limit of approximately twice that required
by the lamp. R

TH2

acts to increase the current limit at turn-

on to approximately 10 times the steady-state lamp current.
The high initial trip point decays away according to a 20ms
time constant contributed by C

. R

TH2

could be eliminated

with C

working against the internal 1k

resistor, but this

results in a very high over-current threshold. As a rule of
thumb design the over-current circuitry in the conventional
manner, then add the R

TH2

network to allow for lamp

start-up. Let R

TH2

= (R

TH1

10)1k

, and choose a capaci-

tor that provides the desired time constant working against
R

TH2

and the internal 1k

resistor.

When the MIC5013 is turned off, the threshold pin (2)
appears as an open circuit, and C

is discharged through

TH1

and R

TH2

. This is much slower than the turn-on time

constant, and it simulates the thermal response of the
filament. If the lamp is pulse-width modulated, the current
limit will be reduced by the residual charge left in C

Modifying Switching Times. Do not add external capaci-
tors to the gate to slow down the switching time. Add a
resistor (1k

to 51k

) in series with the gate of the MOS-

FET to achieve this result.

Bootstrapped High-Side Driver (Figure 6). The speed of
a high-side driver can be increased to better than 10

s by

bootstrapping the supply off of the MOSFET source. This
topology can be used where the load is pulse-width modu-

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

12V

IRCZ44

10µF

3.9k

Figure 5. Time-Variable

Trip Threshold

Control Input

#6014

22k

TH1

22µF

TH2

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

IRF540

10µF

20k

Figure 6. Bootstrapped

High-Side Driver

Control Input

100

R
18m

LOAD

100nF

1N4001 (2)

1N5817

7 to 15V

1mA

R1=

MIC5013

Micrel

MIC5013

July 2000

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

IRFZ40

10µF

20k

Figure 7. 10-Ampere

Electronic Circuit Breaker

100

22m

LOAD

12V

10k

100nF

1N4148

100k

MPSA05

CPSL-3 (Dale)

Applications Information

(Continued)

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

IRFP044 (2)

10µF

20k

Figure 9. 50-Ampere

Industrial Switch

100

LOAD

24V

15k

OFF

330k

100k

24V

LVF-15 (RCD)

CR2943-NA102A
(GE)

100k

Figure 8. Improved

Opto-Isolator Performance

To MIC5013 Input

100k

4N35

33k

33pF

MPSA05

15V

10mA
Control Input

lated (100Hz to 20kHz), or where it is energized for only a
short period of time (

25ms). If the load is left energized for

a long period of time (>25ms), the bootstrap capacitor will
discharge and the MIC5013 supply pin will fall to V+ = V

1.4. Under this condition pins 3 and 4 will be held above V+
and may false trigger the over-current circuit. A larger
capacitor will lengthen the maximum "on" time; 1000

F will

hold the circuit up for 2.5 seconds, but requires more charge
time when the circuit is turned off. The optional Schottky
barrier diode improves turn-on time on supplies of less than
10V.

July 2000

MIC5013

Micrel

Applications Information

(Continued)

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

IRFP250

100µF

6.2k

Figure 10. High-Voltage

Bootstrapped Driver

10m

1N4003

90V

100k

4N35

33k

33pF

MPSA05

10mA
Control Input

15V

1N4003 (2)

15Vp-p, 20kHz

Squarewave

1N4746

100nF
200V

KC1000-4T
(Kelvin)

1/4 HP, 90V

5BPB56HAA100

(GE)

Since the supply current in the "OFF" state is only a small
leakage, the 100nF bypass capacitor tends to remain
charged for several seconds after the MIC5013 is turned off.
In a PWM application the chip supply is actually much
higher than the system supply, which improves switching
time.

Electronic Circuit Breaker (Figure 7). The MIC5013 forms
the basis of a high-performance, fast-acting circuit breaker.
By adding feedback from FAULT to INPUT the breaker can
be made to automatically reset. If an over-current condition
occurs, the circuit breaker shuts off. The breaker tests the
load every 18ms until the short is removed, at which time the
circuit latches ON. No reset button is necessary.

Opto-Isolated Interface (Figure 8). Although the MIC5013
has no special input slew rate requirement, the lethargic
transitions provided by an opto-isolator may cause oscilla-
tions on the rise and fall of the output. The circuit shown
accelerates the input transitions from a 4N35 opto-isolator
by adding hysteresis. Opto-isolators are used where the
control circuitry cannot share a common ground with the
MIC5013 and high-current power supply, or where the
control circuitry is located remotely. This implementation is
intrinsically safe; if the control line is severed the MIC5013
will turn OFF.

Fault-Protected Industrial Switch (Figure 9). The most
common manual control for industrial loads is a push button
on/off switch. The "on" button is physically arranged in a
recess so that in a panic situation the "off" button, which
extends out from the control box, is more easily pressed.
This circuit is compatible with control boxes such as the
CR2943 series (GE). The circuit is configured so that if both
switches close simultaneously, the "off" button has prece-
dence. If there is a fault condition the circuit will latch off, and
it can be reset by pushing the "ON" button.

This application also illustrates how two (or more) MOSFETs
can be paralleled. This reduces the switch drop, and distrib-
utes the switch dissipation into multiple packages.

High-Voltage Bootstrap (Figure 10). Although the MIC5013
is limited to operation on 7 to 32V supplies, a floating
bootstrap arrangement can be used to build a high-side
switch that operates on much higher voltages. The MIC5013
and MOSFET are configured as a low-side driver, but the
load is connected in series with ground. The high speed
normally associated with low-side drivers is retained in this
circuit.

Power for the MIC5013 is supplied by a charge pump. A
20kHz square wave (15Vp-p) drives the pump capacitor
and delivers current to a 100

F storage capacitor. A zener

diode limits the supply to 18V. When the MIC5013 is off,
power is supplied by a diode connected to a 15V supply.
The circuit of Figure 8 is put to good use as a barrier
between low voltage control circuitry and the 90V motor
supply.

Half-Bridge Motor Driver (Figure 11). Closed loop control
of motor speed requires a half-bridge driver. This topology
presents an extra challenge since the two output devices
should not cross conduct (shoot-through) when switching.
Cross conduction increases output device power dissipa-
tion and, in the case of the MIC5013, could trip the over-
current comparator. Speed is also important, since PWM
control requires the outputs to switch in the 2 to 20kHz
range.

The circuit of Figure 11 utilizes fast configurations for both
the top- and bottom-side drivers. Delay networks at each
input provide a 2 to 3

s dead time effectively eliminating

cross conduction. Both the top- and bottom-side drivers are
protected, so the output can be shorted to either rail without
damage.

MIC5013

Micrel

MIC5013

July 2000

Applications Information

(Continued)

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

Fault

V+

Gate

MIC5013

Gnd

Thresh

Sense

Source

Input

IRF541

1µF

20k

Figure 11. Half-Bridge

Motor Driver

100

100nF

1N4001 (2)

1N5817

15V

15k

IRF541

10µF

10k

22m

CPSL-3
(Dale)

22m

CPSL-3
(Dale)

1nF

10k

2N3904

22k

220pF

1N4148

22k

15V

12V,
10A Stalled

PWM

INPUT

The top-side driver is based on the bootstrapped circuit of
Figure 6, and cannot be switched on indefinitely. The
bootstrap capacitor (1

F) relies on being pulled to ground

by the bottom-side output to recharge. This limits the
maximum duty cycle to slightly less than 100%.

Two of these circuits can be connected together to form an
H-bridge. If the H-bridge is used for locked antiphase
control, no special considerations are necessary. In the
case of sign/magnitude control, the "sign" leg of the H-
bridge should be held low (PWM input held low) while the
other leg is driven by the magnitude signal.

If current feedback is required for torque control, it is
available in chopped form at the bottom-side driver's 22 m

current-sensing resistor.

Time-Delay Relay (Figure 12). The MIC5013 forms the
basis of a simple time-delay relay. As shown, the delay
commences when power is applied, but the 100 k

/1N4148

could be independently driven from an external source such

as a switch or another high-side driver to give a delay
relative to some other event in the system.

Hysteresis has been added to guarantee clean switching at
turn-on. Note that an over-current condition latches the
relay in a safe, OFF condition. Operation is restored by
either cycling power or by momentarily shorting pin 1 to
ground.

Motor Driver with Stall Shutdown (Figure 13). Tachom-
eter feedback can be used to shut down a motor driver
circuit when a stall condition occurs. The control switch is a
3-way type; the "START" position is momentary and forces
the driver ON. When released, the switch returns to the
"RUN" position, and the tachometer's output is used to hold
the MIC5013 input ON. If the motor slows down, the tach
output is reduced, and the MIC5013 switches OFF. Resis-
tor "R" sets the shutdown threshold. If the output current
exceeds 30A, the MIC5013 shuts down and remains in that
condition until the momentary "RESET" button is pushed.
Control is then returned to the START/RUN/STOP switch.

MIC5013

Micrel

MIC5013

July 2000

500

12.5V

125pF

100 kHz

OSCILLATOR

OFF

GATE CLAMP

ZENER

Figure 14. Gate Control

Circuit Detail

COM

Applications Information

(Continued)

Q5. For the second phase Q4 turns off and Q3 turns on,
pushing pin C2 above supply (charge is dumped into the
gate). Q3 also charges C1. On the third phase Q2 turns off
and Q1 turns on, pushing the common point of the two
capacitors above supply. Some of the charge in C1 makes
its way to the gate. The sequence is repeated by turning Q2
and Q4 back on, and Q1 and Q3 off.

In a low-side application operating on a 12 to 15V supply,
the MOSFET is fully enhanced by the action of Q5 alone. On
supplies of more than approximately 14V, current flows
directly from Q5 through the zener diode to ground. To
prevent excessive current flow, the MIC5010 supply should
be limited to 15V in low-side applications.

The action of Q5 makes the MIC5013 operate quickly in
low-side applications. In high-side applications Q5
precharges the MOSFET gate to supply, leaving the charge
pump to carry the gate up to full enhancement 10V above
supply. Bootstrapped high-side drivers are as fast as low-
side drivers since the chip supply is boosted well above the
drain at turn-on.

Gate Control Circuit

When applying the MIC5010, it is helpful to understand the
operation of the gate control circuitry (see Figure 14). The
gate circuitry can be divided into two sections: 1) charge
pump (oscillator, Q1-Q5, and the capacitors) and 2) gate
turn-off switch (Q6).

When the MIC5010 is in the OFF state, the oscillator is
turned off, thereby disabling the charge pump. Q5 is also
turned off, and Q6 is turned on. Q6 holds the gate pin (G) at
ground potential which effectively turns the external MOS-
FET off.

Q6 is turned off when the MIC5013 is commanded on. Q5
pulls the gate up to supply (through 2 diodes). Next, the
charge pump begins supplying current to the gate. The gate
accepts charge until the gate-source voltage reaches 12.5V
and is clamped by the zener diode.

A 2-output, three-phase clock switches Q1-Q4, providing a
quasi-tripling action. During the initial phase Q4 and Q2 are
ON. C1 is discharged, and C2 is charged to supply through

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