MIC5021BN [MICREL]
High-Speed High-Side MOSFET Driver; 高速高边MOSFET驱动器
| 型号： | MIC5021BN |
| 厂家： | 
MICREL SEMICONDUCTOR |
| 描述： | High-Speed High-Side MOSFET Driver |
| 文件： | 总9页 (文件大小：135K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC5021
High-Speed High-Side MOSFET Driver
General Description
Features
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.
• 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
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. TheMIC5021thensuppliesalimitedcurrent(< 2mA),
if necessary, to maintain the output state.
Applications
Anovercurrentcomparatorwithatripvoltageof50mVmakes
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
• Lamp control
• Heater control
• Motor control
• Solenoid switching
• Switch-mode power supplies
• Circuit breaker
optional external capacitor placed from the C pin to ground
T
maybeusedtocontrolthecurrentshutdowndutycycle(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
.
Ordering Information
T
DD
5
The MIC5021 is available in 8-pin SOIC and plastic DIP
packages.
Part Number
MIC5021BM
MIC5021BN
Temperature Range
–40°C to +85°C
Package
8-pin SOIC
Other members of the MIC502x family include the MIC5020
low-side driver and the MIC5022 half-bridge driver with a
cross-conduction interlock.
–40°C to +85°C
8-pin Plastic DIP
Typical Application
+12V to +36V
MIC5021
1
2
3
4
8
7
6
5
10µF
TTL Input
optional*
VDD
Input
CT
VBOOST
Gate
N-Channel
Power MOSFET
Sens
Sens
2.7
nF
Gnd
RSENSE
50mV
ITRIP
RSENSE
=
* increases time before retry
High-Side Driver with Overcurrent Trip and Retry
October 1998
5-169
MIC5021
Micrel
Pin Configuration
1 VDD
VBOOST
Gate
8
7
1
2
VDD VBOOST
Gate
CT Sense−
8
7
2 Input
Input
CT
Sense−
Sense+
3
6
5
3
4
6
5
4 Gnd
Gnd
Sense+
DIP Package
(N)
SOIC Package
(M)
Block Diagram
6V Internal Regulator
I1
Fault
CT
CINT
2I1
Normal
VDD
CHARGE
PUMP
VBOOST
Q1
Sense +
15V
Sense –
ON
50mV
OFF
6V
↑
↓
ONE-
SHOT
10I2
I2
Gate
Input
Transistor: 106
Pin Description
Pin Number
Pin Name
Pin Function
1
2
VDD
Supply: +12V to +36V. Decouple with ≥ 10µF capacitor.
Input
TTL Compatible Input: Logic high turns the external MOSFET on. An
internal pull-down returns an open pin to logic low.
3
CT
Retry Timing Capacitor: Controls the off time (tG(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.
4
5
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
RSENSE sets the load overcurrent trip point.
6
7
Sense –
Gate
Current Sense Comparator (–) Input: Connect to the low side of the sense
resistor (usually the high side of the load).
Gate Drive: Drives the gate of an external power MOSFET. Also limits VGS
to 15V max. to prevent Gate-to-Source damage. Will sink and source
current.
8
VBOOST
Charge Pump Boost Capacitor: A bootstrap capacitor from VBOOST to the
FET source pin supplies charge to quickly enhance the Gate output during
turn-on.
5-170
October 1998
MIC5021
Micrel
Absolute Maximum Ratings
Operating Ratings
Supply Voltage (V ) ..................................................+40V
Supply Voltage (V ) .................................... +12V to +36V
DD
DD
Input Voltage ................................................ –0.5V to +15V
Sense Differential Voltage..........................................±6.5V
Sense + or Sense – to Gnd.......................... –0.5V to +36V
Temperature Range
PDIP ....................................................... –40°C to +85°C
SOIC ...................................................... –40°C to +85°C
Timer Voltage (C ) .....................................................+5.5V
T
V
Capacitor .................................................... 0.01µF
BOOST
Electrical Characteristics
TA = 25°C, Gnd = 0V, VDD = 12V, CT = Open, Gate CL = 1500pF (IRF540 MOSFET) unless otherwise specified
Symbol
Parameter
Condition
Min
Typ
1.8
2.5
1.7
2.5
1.4
0.1
20
Max
4
Units
mA
mA
mA
mA
V
D.C. Supply Current
VDD = 12V, Input = 0V
VDD = 36V, Input = 0V
VDD = 12V, Input = 5V
VDD = 36V, Input = 5V
6
4
6
Input Threshold
0.8
2.0
Input Hysteresis
V
Input Pull-Down Current
Current Limit Threshold
Gate On Voltage
Input = 5V
10
30
16
46
2
40
70
µA
mV
V
Note 1
50
VDD = 12V Note 2
18
21
5
VDD = 36V Note 2
50
52
V
tG(ON)
tG(OFF)
tDLH
tR
Gate On Time, Fixed
Gate Off Time, Adjustable
Gate Turn-On Delay
Gate Rise Time
Sense Differential > 70mV
6
10
µs
Sense Differential > 70mV, CT = 0pF
10
20
50
µs
Note 3
Note 4
Note 5
Note 6
Note 7
500
400
800
400
150
1000
500
1500
500
ns
ns
tDLH
tF
Gate Turn-Off Delay
Gate Fall Time
ns
ns
fmax
Maximum Operating Frequency
100
kHz
Note 1 When using sense MOSFETs, it is recommended that R
Note 2 DC measurement.
< 50Ω. Higher values may affect the sense MOSFET’s current transfer ratio.
SENSE
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.
October 1998
5-171
MIC5021
Micrel
Typical Characteristics
Gate Voltage Change
vs. Supply Voltage
Gate Turn-On Delay vs.
Supply Voltage
Supply Current vs.
Supply Voltage
2.5
25
20
15
10
5
900
850
800
750
700
650
VGATE = VSUPPLY + 4V
VGATE = VGATE – VSUPPLY
VIN = 0V
2.0
CL = 1500pF (IRCZ34)
CBOOST = 0.01µF
1.5
VIN = 5V
1.0
0.5
0.0
INCLUDES PROPAGATION DELAY
0
5
10 15 20 25 30 35 40
5
10 15 20 25 30 35 40
(V)
5
10 15 20 25 30 35 40
V
(V)
V
V
(V)
SUPPLY
SUPPLY
SUPPLY
Gate Turn-On Delay vs.
Supply Voltage
Gate Turn-On Delay vs.
Gate Capacitance
Gate Turn-Off Delay vs.
Supply Voltage
1000
950
900
850
800
750
2.5
2.0
1.5
1.0
0.5
0.0
2000
1750
1500
1250
1000
750
VGATE = VSUPPLY + 4V
VGATE = VSUPPLY + 4V
VSUPPLY = 12V
VGATE = VSUPPLY + 10V
RL = 400
CL = 1500pF (IRCZ34)
CBOOST = 0.01µF
CGATE = 1500pF
(IRCZ34)
INCLUDES PROPAGATION DELAY
INCLUDES PROPAGATION DELAY
INCLUDES PROPAGATION DELAY
5
10 15 20 25 30 35 40
0
1
2
3
4
5
5
10 15 20 25 30 35 40
1x10 1x10 1x10 1x10 1x10 1x10
(pF)
V
(V)
V
(V)
C
SUPPLY
SUPPLY
GATE
Overcurrent Retry Duty
Cycle vs. Timing Capacitance
Sense Threshold vs.
Temperature
Input Current vs.
Input Voltage
25
100
80
60
40
20
0
80
70
60
50
40
30
20
VSUPPLY = 12V
tON = 5µs
V
SUPPLY = 12V
20
15
10
5
NOTE:
tON, tOFF TIME
INDEPENDENT
OF VSUPPLY
0
0
5
10
V
15
(V)
20
25
-60 -30
0
30 60 90 120 150
0.1
1
10
C
100 1000 10000
(pF)
TEMPERATURE (°C)
IN
T
TTL (H)
0V
Input
Gate
15V (max.)
Source
50mV
Sense +, –
Differential
0V
Timing Diagram 1. Normal Operation
6µs
20µs
6µs
TTL (H)
0V
TTL (H)
Input
Gate
Input
Gate
0V
15V (max.)
Source
50mV
15V (max.)
Source
50mV
Sense +, –
Differential
Sense +, –
Differential
0V
0V
Timing Diagram 2. Fault Condition, C = Open
Timing Diagram 3. Fault Condition, C = Grounded
T
T
5-172
October 1998
MIC5021
Micrel
An internal zener diode protects the external MOSFET by
limiting the gate to source voltage.
Functional Description
Refer to the MIC5021 block diagram.
Input
Sense Inputs
The MIC5021’s 50mV (nominal) trip voltage is created by
internal current sources that force approximately 5µA out of
SENSE + and approximately 15µA (at trip) out of SENSE –.
When SENSE – is 50mV or more below SENSE +, SENSE –
steals base current from an internal drive transistor shutting
off the external MOSFET.
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
Overcurrent Limiting
Rapid rise and fall times on the GATE output are possible
because each input state change triggers a one-shot which
Current source I charges C
externalcapacitorconnectedtoC iskeptdischargedthrough
a MOSFET Q1.
upon power up. An optional
INT
1
T
activatesahigh-valuecurrentsink(10I )forashorttime. This
2
draws a high current though a current mirror circuit causing
the output transistors to quickly charge or discharge the
external MOSFET’s gate.
A fault condition (> 50mV from SENSE + to SENSE –) causes
the overcurrent comparator to enable current sink 2I which
1
overcomescurrentsourceI todischargeC inashorttime.
1
INT
A second current sink continuously draws the lower value of
current used to maintain the gate voltage for the selected
state.
When C
is discharged, the INPUT is disabled, which turns
INT
off the gate output, and C and C are ready to be charged.
INT
T
When the gate output turns the MOSFET off, the overcurrent
signal is removed from the sense inputs which deactivates
Aninternalchargepumputilizesanexternal“boost”capacitor
connected between V
and the source of the external
current sink 2I . This allows C
and the optional capacitor
BOOST
1
INT
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
connected to C to recharge. A Schmitt trigger delays the
T
retry while the capacitor(s) recharge. Retry delay is in-
creased by connecting a capacitor to C (optional).
T
to the voltage across the capacitor, raising the V
pin
BOOST
The retry cycle will continue until the fault is removed or the
input is changed to TTL low.
voltage. The boost capacitor charge is directed through the
GATE pin to quickly charge the MOSFET’s gate to 16V
5
If C is connected to ground, the circuit will not retry upon a
T
maximum above V . The internal charge pump maintains
DD
fault condition.
the gate voltage.
Supply Voltage
Applications Information
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.
DD
The MIC5021 MOSFET driver is intended for high-side
switching applications where overcurrent limiting and high
speedarerequired. TheMIC5021cancontrolMOSFETsthat
switch voltages up to 36V.
A 16V minimum supply is recommended to produce continu-
ous on-state, gate drive voltage for standard MOSFETs (10V
nominal gate enhancement).
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.
Whenthedriverispoweredfroma12Vto16Vsupply, alogic-
level MOSFET is recommended (5V nominal gate enhance-
ment).
PWMoperationmayproducesatisfactorygateenhancement
at lower supply voltages. This occurs when fast switching
repetition makes the boost capacitor a more significant
voltage supply than the internal charge pump.
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.)
October 1998
5-173
MIC5021
Micrel
Logic-Level MOSFET Precautions
A 0.01µF boost capacitor is recommended for best perfor-
mance in the 12V to 20V range. Refer to figure 1. Larger
capacitors may damage the MIC5021.
Logic-level MOSFETs have lower maximum gate-to-source
voltage ratings (typically ±10V) than standard MOSFETs
(typically±20V). WhenanexternalMOSFETisturnedon,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,
+12V to +36V
MIC5021
1
2
3
4
8
7
6
5
10µF
VDD
Input
CT
VBOOST
Gate
TTL Input
connect a zener diode (5V≤V
<10V) from gate to source.
Zener
2.7
nF
Sens
Sens
Overcurrent Limiting
Gnd
A 50mV comparator is provided for current sensing. The low
2
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.
T
C to ground maintains gate drive shutdown following an
overcurrent condition.
T
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
C open, or a capacitor to ground, causes automatic retry.
T
Thedefaultdutycycle(C open)isapproximately20%. Refer
T
to the electrical characteristics when selecting a capacitor for
reduced duty cycle.
to place the capacitor is placed between V and V
as
DD
BOOST
shown in Figure 3.
C through a pull-up resistor to V increases the duty cycle.
T
DD
+12V to +36V
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
0.1
µF
MIC5021
1
2
3
4
8
7
6
5
10µF
VDD
Input
CT
VBOOST
Gate
TTL Input
damaged if the voltage applied to C exceeds the absolute
T
maximum voltage rating.
Sens
Sens
Boost Capacitor Selection
Gnd
The boost capacitor value will vary depending on the supply
voltage range.
+12V to +20V
MIC5021
1
2
3
4
8
7
6
5
10µF
VDD
Input
CT
VBOOST
Gate
Figure 3. Preferred 20V to 36V Configuration
Do not use both boost capacitor between V and the
TTL Input
0.01
µF
BOOST
Sens
Sens
MOSFET source and V
and V at the same time.
BOOST
DD
Gnd
Current Sense Resistors
Lead length can be significant when using low value (< 1Ω)
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.
Figure 1. 12V to 20V Configuration
5-174
October 1998
MIC5021
Micrel
Circuits Without Current Sensing
The diode should have a peak forward current rating greater
thantheloadcurrent. Thisisbecausethecurrentthroughthe
diode is the same as the load current at the instant the
MOSFET is turned off.
V+
MIC5021
1
2
3
4
8
7
6
5
10µF
TTL Input
+20V to +36V
(+24V)
VDD
Input
CT
VBOOST
Gate
N-Channel
Power MOSFET
0.01
µF
MIC5021
Sense−
Sense+
1
2
3
4
8
7
6
5
10µF
TTL Input
0.01
µF
VDD
Input
CT
VBOOST
Gate
Gnd
N-Channel
Power MOSFET
(IRF540)
Load
Sens
Sens
Gnd
Figure 4a. Connecting Sense to Source
RSENSE
(< 0.08Ω)
V+
Solenoid
(24V, 47Ω)
Schottky
Diode
(1N5822)
MIC5021
1
2
3
4
8
7
6
5
10µF
TTL Input
VDD
Input
CT
VBOOST
Gate
N-Channel
Power MOSFET
Sense−
Sense+
Figure 5. Solenoid Driver
with Current Sensing
0.01
µF
Gnd
Load
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.
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
forinductiveloads. DonotconnecttheSENSE pinstoground.
MIC5021
1
2
3
4
8
7
6
5
VDD
Input
CT
5
Gate
Inductive Load Precautions
MOSFET
Turnoff
Circuitscontrollinginductiveloads,suchassolenoids(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.
~V
0V
DD
Negative
Spike
Forward drop across diodes
allows leads to go negative.
Inductive
Load
Current flows from ground (0V)
through the diodes to the load
during negative transcients.
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
(theMOSFETappearsasaveryhighresistance)averylarge
negative voltage occurs across the inductor.
Figure 6. Inductive Load Turnoff
Figure 6 shows current flowing out of the sense leads of an
MIC5021duringanegativetransient(inductivekick). Internal
Schottky diodes attempt to limit the negative transient by
maintaining a low forward drop.
Limiting Inductive Spikes
The voltage across the inductor can be limited by connecting
aSchottkydiodeacrosstheload. Thediodeisforwardbiased
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
transientfromdamagingthechargepumpbywayoftheboost
capacitor. Also see Sense Pin Considerations below.
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.
October 1998
5-175
MIC5021
Micrel
External Protection
High-Side Sensing
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.
Sensing the current on the high side of the MOSFET isolates
the SENSE pins from the inductive spike.
+12V to +20V
(+12V)
MIC5021
MIC5021
RSENSE
(< 0.01Ω)
1
2
3
4
8
7
6
5
1
2
3
4
8
7
6
5
10µF
TTL Input
VDD
Input
CT
VBOOST
Gate
VDD
Input
CT
VBOOST
Gate
N-Channel
Power MOSFET
N-Channel
Power MOSFET
(IRFZ44)
Sense−
Sense+
Sens
Sens
R1
Gnd
Gnd
5µA
VR1
R2
0.01
µF
50mV nominal
RS
(at trip)
Wirewound
Resistor
(3Ω)
VR1 = VR2
to avoid skewing
the 50mV trip point..
15µA
VR2
(5mV suggested)
R1 3 × R2
Figure 9. High Side Sensing
Lamp Driver Application
Figure 7. Resistor Voltage Drop
Duringnormaloperation,sensingcurrentfromthesensepins
is unequal (5µA and 15µA). 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.
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.
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.
V+
(+12V)
MIC5021
+12V to +36V
1
2
3
4
8
7
6
5
10µF
TTL Input
VDD
Input
CT
VBOOST
Gate
N-Channel
Power MOSFET
(IRF540)
MIC5021
1
2
3
4
8
7
6
5
10µF
Sense−
Sense+
VDD
Input
CT
VBOOST
Gate
0.01
µF
Gnd
N-Channel
Power MOSFET
TTL Input
2.7
nF
RSENSE
(0.041Ω)
Sens
Sens
R1
Gnd
1.0k
Incandescent
Lamp (#1157)
"( )" values apply to demo circuit.
See text.
D2
RSENSE
11DQ03
R2
330Ω
D3
11DQ03
Figure 10. Lamp Driver with
Current Sensing
Inductive
Load
D1
A lamp may not fully turn on if the filament does not heat up
adequately. Changing the duty cycle, sense resistor, or both
tomatchthefilamentcharacteristicscancorrecttheproblem.
Soft start can be demonstrated using a #1157 dual filament
Figure 8. Protection from Inductive Kick
automotive lamp. The value of R shown in Figure 10 allows
S
for soft start of the higher-resistance filament (measures
approx. 2.1Ω cold or 21Ω hot).
5-176
October 1998
MIC5021
Micrel
+12V to +36V
Remote Overcurrent Limiting Reset
In circuit breaker applications where the MIC5021 maintains
an off condition after an overcurrent condition is sensed, the
MIC5021AJB
1
2
3
4
8
7
6
5
10µF
TTL Input
VDD
Input
CT
VBOOST
Gate
C pin can be used to reset the MIC5021.
T
+12V to +20V
Sens
Sens
2.7
nF
2.2M
MIC5021
Gnd
1
2
3
4
8
7
6
5
10µF
TTL Input
VDD
Input
CT
VBOOST
Gate
RSENSE
N-Channel
Power
add resistor for
–40°C to –55°C
operation
10k to
100k
MOSFET
Sens
Sens
0.01
µF
2N3904
Q1
Gnd
74HC04
(example)
RSENSE
Retry (H)
Maintained (L)
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.
Figure 11. Remote Control Circuit
+12V to +36V
SwitchingQ1onpullsC lowwhichkeepstheMIC5021GATE
T
MIC5021AJB
output off when an overcurrent is sensed. Switching Q1 off
causes C to appear open. The MIC5021 retries in about
20µs and continues to retry until the overcurrent condition is
1
2
3
4
8
7
6
5
10µF
TTL Input
VDD
Input
CT
VBOOST
Gate
T
removed.
Sens
Sens
2.7
nF
For demonstration purposes, a 680Ω load resistor and 3Ω
senseresistorwillproduceanovercurrentconditionwhenthe
load’s supply (V+) is approximately 12V or greater.
Gnd
RSENSE
5
Low-Temperature Operation
add resistor for
–40°C to –55°C
operation
2.2M
As the temperature of the MIC5021AJB (extended tempera-
ture range version—no longer available) approaches –55°C,
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
2.2MΩ 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.
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.
October 1998
5-177
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