October 1998

MIC5021

Micrel

MIC5021

High-Speed High-Side MOSFET Driver

Final Information

Ordering Information

Part Number

Temperature Range

Package

MIC5021BM

C to +85

8-pin SOIC

MIC5021BN

C to +85

8-pin Plastic DIP

Features

· 12V to 36V operation
· 550ns rise/fall time driving 2000pF
· TTL compatible input with internal pull-down resistor
· Overcurrent limit
· Gate to source protection
· Internal charge pump
· 100kHz operation guaranteed over full temperature and

operating voltage range

· Compatible with current sensing MOSFETs
· Current source drive reduces EMI

Applications

· Lamp control
· Heater control
· Motor control
· Solenoid switching
· Switch-mode power supplies
· Circuit breaker

General Description

The MIC5021 high-side MOSFET driver is designed to oper-
ate at frequencies up to 100kHz (5kHz PWM for 2% to 100%
duty cycle) and is an ideal choice for high speed applications
such as motor control, SMPS (switch mode power supplies),
and applications using IGBTs. The MIC5021 can also
operate as a circuit breaker with or without automatic retry.

A rising or falling edge on the input results in a current source
pulse or sink pulse on the gate output. This output current
pulse can turn on a 2000pF MOSFET in approximately
550ns. The MIC5021 then supplies a limited current (< 2mA),
if necessary, to maintain the output state.

An overcurrent comparator with a trip voltage of 50mV makes
the MIC5021 ideal for use with a current sensing MOSFET.
An external low value resistor may be used instead of a
sensing MOSFET for more precise overcurrent control. An
optional external capacitor placed from the C

pin to ground

may be used to control the current shutdown duty cycle (dead
time) from 20% to < 1%. A duty cycle from 20% to about 75%
is possible with an optional pull-up resistor from C

to V

The MIC5021 is available in 8-pin SOIC and plastic DIP
packages.

Other members of the MIC502x family include the MIC5020
low-side driver and the MIC5022 half-bridge driver with a
cross-conduction interlock.

Typical Application

Input

Gnd

BOOST

Gate

Sense

TTL Input

SENSE

N-Channel
Power MOSFET

+12V to +36V

MIC5021

10µF

2.7

Load

SENSE =

50mV

TRIP

* increases time before retry

optional*

High-Side Driver with Overcurrent Trip and Retry

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

MIC5021

Micrel

MIC5021

October 1998

Pin Description

Pin Number

Pin Name

Pin Function

Supply: +12V to +36V. Decouple with

F capacitor.

Input

TTL Compatible Input: Logic high turns the external MOSFET on. An
internal pull-down returns an open pin to logic low.

Retry Timing Capacitor: Controls the off time (t

G(OFF)

) of the overcurrent

retry cycle. (Duty cycle adjustment.)
· Open = approx. 20% duty cycle.
· Capacitor to Ground = approx. 20% to < 1% duty cycle.
· Pull-up resistor = approx. 20% to approx. 75% duty cycle.
· Ground = maintained shutdown upon overcurrent condition.

Gnd

Circuit Ground

Sense +

Current Sense Comparator (+) Input: Connect to high side of sense resistor
or current sensing MOSFET sense lead. A built-in offset in conjunction with
R

SENSE

sets the load overcurrent trip point.

Sense

Current Sense Comparator () Input: Connect to the low side of the sense
resistor (usually the high side of the load).

Gate

Gate Drive: Drives the gate of an external power MOSFET. Also limits V

to 15V max. to prevent Gate-to-Source damage. Will sink and source
current.

BOOST

Charge Pump Boost Capacitor: A bootstrap capacitor from V

BOOST

to the

FET source pin supplies charge to quickly enhance the Gate output during
turn-on.

Pin Configuration

Input

Gnd

BOOST

Gate

Sense

BOOST

Gate

Sense

Input

Gnd

Block Diagram

Sense

Sense +

6V Internal Regulator

INT

50mV

Input

ONE-

SHOT

Gate

OFF

Fault

Normal

10I

15V

CHARGE

PUMP

BOOST

Transistor: 106

DIP Package

SOIC Package

(N)

(M)

October 1998

MIC5021

Micrel

Electrical Characteristics

= 25

C, Gnd = 0V, V

= 12V, C

= Open, Gate C

= 1500pF (IRF540 MOSFET) unless otherwise specified

Symbol

Parameter

Condition

Min

Typ

Max

Units

D.C. Supply Current

= 12V, Input = 0V

1.8

= 36V, Input = 0V

2.5

= 12V, Input = 5V

1.7

= 36V, Input = 5V

2.5

Input Threshold

0.8

1.4

2.0

Input Hysteresis

0.1

Input Pull-Down Current

Input = 5V

Current Limit Threshold

Note 1

Gate On Voltage

= 12V Note 2

= 36V Note 2

G(ON)

Gate On Time, Fixed

Sense Differential > 70mV

G(OFF)

Gate Off Time, Adjustable

Sense Differential > 70mV, C

= 0pF

DLH

Gate Turn-On Delay

Note 3

500

1000

Gate Rise Time

Note 4

400

500

DLH

Gate Turn-Off Delay

Note 5

800

1500

Gate Fall Time

Note 6

400

500

max

Maximum Operating Frequency

Note 7

100

150

kHz

Note 1

When using sense MOSFETs, it is recommended that R

SENSE

< 50

. Higher values may affect the sense MOSFET's current transfer ratio.

Note 2

DC measurement.

Note 3

Input switched from 0.8V (TTL low) to 2.0V (TTL high), time for Gate transition from 0V to 2V.

Note 4

Input switched from 0.8V (TTL low) to 2.0V (TTL high), time for Gate transition from 2V to 17V.

Note 5

Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 20V (Gate on voltage) to 17V.

Note 6

Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 17V to 2V.

Note 7

Frequency where gate on voltage reduces to 17V with 50% input duty cycle.

Absolute Maximum Ratings

Supply Voltage (V

) .................................................. +40V

Input Voltage ................................................ 0.5V to +15V

Sense Differential Voltage ..........................................

6.5V

Sense + or Sense to Gnd .......................... 0.5V to +36V

Timer Voltage (C

) ..................................................... +5.5V

BOOST

Capacitor .................................................... 0.01

Operating Ratings

Supply Voltage (V

) .................................... +12V to +36V

Temperature Range

PDIP ....................................................... 40

C to +85

SOIC ...................................................... 40

C to +85

MIC5021

Micrel

MIC5021

October 1998

0.0

0.5

1.0

1.5

2.0

2.5

SUPPLY

(mA)

SUPPLY

(V)

Supply Current vs.

Supply Voltage

= 0V

= 5V

650

700

750

800

850

900

ON 4V

(ns)

SUPPLY

(V)

Gate Turn-On Delay vs.

Supply Voltage

GATE

= V

SUPPLY

+ 4V

= 1500pF (IRCZ34)

BOOST

= 0.01

INCLUDES PROPAGATION DELAY

750

800

850

900

950

1000

ON 10V

(ns)

SUPPLY

(V)

Gate Turn-On Delay vs.

Supply Voltage

GATE

= V

SUPPLY

+ 10V

= 1500pF (IRCZ34)

BOOST

= 0.01

INCLUDES PROPAGATION DELAY

0.0

0.5

1.0

1.5

2.0

2.5

1x10

(

GATE

(pF)

Gate Turn-On Delay vs.

Gate Capacitance

GATE

= V

SUPPLY

+ 4V

SUPPLY

= 12V

INCLUDES PROPAGATION DELAY

750

1000

1250

1500

1750

2000

OFF 4V

(ns)

SUPPLY

(V)

Gate Turn-Off Delay vs.

Supply Voltage

GATE

= V

SUPPLY

+ 4V

= 400

INCLUDES PROPAGATION DELAY

GATE

= 1500pF

(IRCZ34)

0.1

100

1000 10000

RETRY DUTY CYCLE (%)

(pF)

NOTE:
t

, t

OFF

TIME

INDEPENDENT
OF V

SUPPLY

Overcurrent Retry Duty

Cycle vs. Timing Capacitance

= 5

SUPPLY

= 12V

GATE

(V)

SUPPLY

(V)

Gate Voltage Change

vs. Supply Voltage

GATE

= V

GATE

SUPPLY

100

(

(V)

Input Current vs.

Input Voltage

SUPPLY

= 12V

Typical Characteristics

Timing Diagram 2. Fault Condition, C

= Open

Timing Diagram 3. Fault Condition, C

= Grounded

Input

TTL (H)

Source

50mV

Sense +, 

Differential

Gate

15V (max.)

6µs

20µs

Input

TTL (H)

Source

50mV

Sense +, 

Differential

Gate

15V (max.)

6µs

Input

TTL (H)

Source

50mV

Sense +, 

Differential

Gate

15V (max.)

Timing Diagram 1. Normal Operation

-60 -30

90 120 150

VOLTAGE (mV)

TEMPERATURE (

Sense Threshold vs.

Temperature

October 1998

MIC5021

Micrel

Functional Description

Refer to the MIC5021 block diagram.

Input

A signal greater than 1.4V (nominal) applied to the MIC5021

INPUT

causes gate enhancement on an external MOSFET

turning the MOSFET on.

An internal pull-down resistor insures that an open

INPUT

remains low, keeping the external MOSFET turned off.

Gate Output

Rapid rise and fall times on the

GATE

output are possible

because each input state change triggers a one-shot which
activates a high-value current sink (10I

) for a short time. This

draws a high current though a current mirror circuit causing
the output transistors to quickly charge or discharge the
external MOSFET's gate.

A second current sink continuously draws the lower value of
current used to maintain the gate voltage for the selected
state.

An internal charge pump utilizes an external "boost" capacitor
connected between V

BOOST

and the source of the external

MOSFET. (Refer to typical application.) The boost capacitor
stores charge when the MOSFET is off. As the MOSFET
turns on, its source to ground voltage increases and is added
to the voltage across the capacitor, raising the V

BOOST

voltage. The boost capacitor charge is directed through the

GATE

pin to quickly charge the MOSFET's gate to 16V

maximum above V

. The internal charge pump maintains

the gate voltage.

An internal zener diode protects the external MOSFET by
limiting the gate to source voltage.

Sense Inputs

The MIC5021's 50mV (nominal) trip voltage is created by
internal current sources that force approximately 5

A out of

SENSE

+ and approximately 15

A (at trip) out of

SENSE

When

SENSE

is 50mV or more below

SENSE

steals base current from an internal drive transistor shutting
off the external MOSFET.

Overcurrent Limiting

Current source I

charges C

INT

upon power up. An optional

external capacitor connected to C

is kept discharged through

a MOSFET Q1.

A fault condition (> 50mV from

SENSE

+ to

SENSE

) causes

the overcurrent comparator to enable current sink 2I

which

overcomes current source I

to discharge C

INT

in a short time.

When C

INT

is discharged, the

INPUT

is disabled, which turns

off the gate output, and C

INT

and C

are ready to be charged.

When the gate output turns the MOSFET off, the overcurrent
signal is removed from the sense inputs which deactivates
current sink 2I

. This allows C

INT

and the optional capacitor

connected to C

to recharge. A Schmitt trigger delays the

retry while the capacitor(s) recharge. Retry delay is in-
creased by connecting a capacitor to C

(optional).

The retry cycle will continue until the fault is removed or the
input is changed to TTL low.

If C

is connected to ground, the circuit will not retry upon a

fault condition.

Supply Voltage

The MIC5021's supply input (V

) 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 continu-
ous 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 enhance-
ment).

PWM operation may produce satisfactory gate enhancement
at lower supply voltages. This occurs when fast switching
repetition makes the boost capacitor a more significant
voltage supply than the internal charge pump.

Applications 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.

High-Side Switch Circuit Advantages

High-side switching allows more of the load related compo-
nents and wiring to remain near ground potential when
compared to low-side switching. This reduces the chances
of short-to-ground accidents or failures.

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 modu-
lation) designs used for motor control, 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.)

MIC5021

Micrel

MIC5021

October 1998

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

Zener

<10V) from gate to source.

Overcurrent Limiting

A 50mV comparator is provided for current sensing. The low
level trip point minimizes I

R 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 heating elements, and
can be adjusted from the C

connection.

to ground maintains gate drive shutdown following an

overcurrent condition.

open, or a capacitor to ground, causes automatic retry.

The default duty cycle (C

open) is approximately 20%. Refer

to the electrical characteristics when selecting a capacitor for
reduced duty cycle.

through a pull-up resistor to V

increases the duty cycle.

Increasing the duty cycle increases the power dissipation in
the load and MOSFET under a "fault" condition. Circuits may
become unstable at a duty cycle of about 75% or higher,
depending on conditions.

Caution: The MIC5021 may be

damaged if the voltage applied to C

exceeds the absolute

maximum voltage rating.

Boost Capacitor Selection

The boost capacitor value will vary depending on the supply
voltage range.

Input

Gnd

BOOST

Gate

Sense

TTL Input

+12V to +20V

MIC5021

10µF

0.01

µF

Load

Figure 1. 12V to 20V Configuration

A 0.01

F boost capacitor is recommended for best perfor-

mance in the 12V to 20V range. Refer to figure 1. Larger
capacitors may damage the MIC5021.

Input

Gnd

BOOST

Gate

Sense

TTL Input

+12V to +36V

MIC5021

10µF

2.7

Load

Figure 2. 12V to 36V Configuration

If the full 12V to 36V voltage range is required, the boost
capacitor value must be reduced to 2.7nF. Refer to Figure 2.
The recommended configuration for the 20V to 36V range is
to place the capacitor is placed between V

and V

BOOST

shown in Figure 3.

Input

Gnd

BOOST

Gate

Sense

TTL Input

+12V to +36V

MIC5021

10µF

Load

0.1
µF

Figure 3. Preferred 20V to 36V Configuration

Do not use both boost capacitor between V

BOOST

and the

MOSFET source and V

BOOST

and V

at the same time.

Current Sense Resistors

Lead length can be significant when using low value (< 1

)

resistors for current sensing. Errors caused by lead length
can be avoided by using four-teminal current sensing resis-
tors. Four-terminal resistors are available from several
manufacturers.

October 1998

MIC5021

Micrel

The diode should have a peak forward current rating greater
than the load current. This is because the current through the
diode is the same as the load current at the instant the
MOSFET is turned off.

Input

Gnd

BOOST

Gate

Sense

TTL Input

SENSE

N-Channel
Power MOSFET
(IRF540)

+20V to +36V

MIC5021

10µF

Solenoid

(24V, 47

)

0.01
µF

Schottky
Diode
(1N5822)

(+24V)

(< 0.08

)

Figure 5. Solenoid Driver

with Current Sensing

Sense Pin Considerations

The sense pins of the MIC5021 are sensitive to negative
voltages. Forcing the sense pins much below 0.5V effec-
tively reverses the supply voltage on portions of the driver
resulting in unpredictable operation or damage.

MOSFET

Turnoff

Negative
Spike

Input

Gate

MIC5021

Inductive
Load

Current flows from ground (0V)
through the diodes to the load
during negative transcients.

Forward drop across diodes
allows leads to go negative.

Figure 6. Inductive Load Turnoff

Figure 6 shows current flowing out of the sense leads of an
MIC5021 during a negative transient (inductive kick). Internal
Schottky diodes attempt to limit the negative transient by
maintaining a low forward drop.

Although the internal Schottky diodes can protect the driver
in low-current resistive applications, they are inadequate for
inductive loads or the lead inductance in high-current resis-
tive loads. Because of their small size, the diodes' forward
voltage drop quickly exceeds 0.5V as current increases.

Circuits Without Current Sensing

Input

Gnd

BOOST

Gate

Sense

TTL Input

Load

N-Channel
Power MOSFET

V+

MIC5021

10µF

0.01
µF

Figure 4a. Connecting Sense to Source

Input

Gnd

BOOST

Gate

Sense

TTL Input

Load

N-Channel
Power MOSFET

V+

MIC5021

10µF

0.01
µF

Figure 4b. Connecting Sense to Supply

Current sensing may be omitted by connecting the

SENSE

and

SENSE

pins to the source of the MOSFET or to the

supply. Connecting the

SENSE

pins to the supply is preferred

for inductive loads. Do not connect the

SENSE

pins to ground.

Inductive Load Precautions

Circuits controlling inductive loads, such as solenoids (Figure
5) and motors, require precautions when controlled by the
MIC5021. Wire wound resistors, which are sometimes used
to simulate other loads, can also show significant inductive
properties.

An inductive load releases stored energy when its current
flow is interrupted (when the MOSFET is switched off). The
voltage across the inductor reverses and the inductor at-
tempts to force current flow. Since the circuit appears open
(the MOSFET appears as a very high resistance) a very large
negative voltage occurs across the inductor.

Limiting Inductive Spikes

The voltage across the inductor can be limited by connecting
a Schottky diode across the load. The diode is forward biased
only when the load is switched off. The Schottky diode
clamps negative transients to a few volts. This protects the
MOSFET from drain-to-source breakdown and prevents the
transient from damaging the charge pump by way of the boost
capacitor. Also see

Sense Pin Considerations below.

MIC5021

Micrel

MIC5021

October 1998

External Protection

Resistors placed in series with each

SENSE

connection limit

the current drawn from the internal Schottky diodes during a
negative transient. This minimizes the forward drop across
the diodes.

Input

Gnd

BOOST

Gate

Sense

N-Channel
Power MOSFET

MIC5021

Load

5µA

15µA

= V

to avoid skewing
the 50mV trip point.

(5mV suggested)

50mV nominal
(at trip)

Figure 7. Resistor Voltage Drop

During normal operation, sensing current from the sense pins
is unequal (5

A and 15

A). The internal Schottky diodes are

reverse biased and have no effect. To avoid skewing the trip
voltage, the current limiting resistors must drop equal volt-
ages at the trip point currents. See Figure 7. To minimize
resistor tolerance error, use a voltage drop lower than the trip
voltage of 50mV. 5mV is suggested.

External Schottky diodes are also recommended. See D2
and D3 in Figure 8. The external diodes clamp negative
transients better than the internal diodes because their larger
size minimizes the forward voltage drop at higher currents.

Input

Gnd

BOOST

Gate

Sense

TTL Input

Inductive
Load

N-Channel
Power MOSFET

+12V to +36V

MIC5021

10µF

2.7

SENSE

1.0k

330

11DQ03

Figure 8. Protection from Inductive Kick

High-Side Sensing

Sensing the current on the high side of the MOSFET isolates
the

SENSE

pins from the inductive spike.

Input

Gnd

BOOST

Gate

Sense

TTL Input

Wirewound
Resistor
(3

)

N-Channel
Power MOSFET
(IRFZ44)

+12V to +20V

SENSE

(< 0.01

)

(+12V)

MIC5021

10µF

0.01

µF

Figure 9. High Side Sensing

Lamp Driver Application

Incandescent lamps have a high inrush current (low resis-
tance) when turned on. The MIC5021 can perform a "soft
start" by pulsing the MOSFET (overcurrent condition) until
the filament is warm and its current decreases (resistance
increases). The sense resistor value is selected so the
voltage drop across the sense resistor decreases below the
sense threshold (50mV) as the filament becomes warm. The
FET is no longer pulsed and the lamp turns completely on.

Input

Gnd

BOOST

Gate

Sense

TTL Input

SENSE

(0.041

)

N-Channel

Power MOSFET
(IRF540)

V+

MIC5021

10µF

0.01

µF

Incandescent

Lamp (#1157)

(+12V)

"( )" values apply to demo circuit.

See text.

Figure 10. Lamp Driver with

Current Sensing

A lamp may not fully turn on if the filament does not heat up
adequately. Changing the duty cycle, sense resistor, or both
to match the filament characteristics can correct the problem.

Soft start can be demonstrated using a #1157 dual filament
automotive lamp. The value of R

shown in Figure 10 allows

for soft start of the higher-resistance filament (measures
approx. 2.1

cold or 21

hot).

October 1998

MIC5021

Micrel

Remote Overcurrent Limiting Reset

In circuit breaker applications where the MIC5021 maintains
an off condition after an overcurrent condition is sensed, the
C

pin can be used to reset the MIC5021.

Input

Gnd

BOOST

Gate

Sense

TTL Input

SENSE

N-Channel
Power

MOSFET

+12V to +20V

MIC5021

10µF

0.01
µF

Load

74HC04

(example)

2N3904
Q1

10k to

100k

Retry (H)

Maintained (L)

Figure 11. Remote Control Circuit

Switching Q1 on pulls C

low which keeps the MIC5021

GATE

output off when an overcurrent is sensed. Switching Q1 off
causes C

to appear open. The MIC5021 retries in about

s and continues to retry until the overcurrent condition is

removed.

For demonstration purposes, a 680

load resistor and 3

sense resistor will produce an overcurrent condition when the
load's supply (V+) is approximately 12V or greater.

Low-Temperature Operation

As the temperature of the MIC5021AJB (extended tempera-
ture range version--no longer available) approaches 55

the driver's off-state, gate-output offset from ground in-
creases. If the operating environment of the MIC5021AJB
includes low temperatures (40

C to 55

C), add an external

2.2M

resistor as shown in Figures 12a or 12b. This assures

that the driver's gate-to-source voltage is far below the
external MOSFET's gate threshold voltage, forcing the
MOSFET fully off.

Input

Gnd

BOOST

Gate

Sense

TTL Input

SENSE

+12V to +36V

MIC5021AJB

10µF

2.7

Load

2.2M

add resistor for

40

C to 55

operation

Figure 12a. Gate-to-Source Pull Down

The gate-to-source configuration (refer to Figure 12a) is
appropriate for resistive and inductive loads. This also
causes the smallest decrease in gate output voltage.

Input

Gnd

BOOST

Gate

Sense

TTL Input

SENSE

+12V to +36V

MIC5021AJB

10µF

2.7

Load

2.2M

add resistor for

40

C to 55

operation

Figure 12b. Gate-to-Ground Pull Down

The gate-to-ground configuration (refer to Figure 12b) is
appropriate for resistive, inductive, or capacitive loads. This
configuration will decrease the gate output voltage slightly
more than the circuit shown in Figure 12a.

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: MIC5021B

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: MIC5021B