Micrel MIC5021BN High-speed high-side mosfet driver Datasheet

MIC5021
Micrel
MIC5021
High-Speed High-Side MOSFET Driver
General Description
Features
The MIC5021 high-side MOSFET driver is designed to operate 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 CT 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 CT to VDD.
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.
•
•
•
•
•
•
•
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
Ordering Information
Temperature Range
Package
MIC5021BM
–40°C to +85°C
8-pin SOIC
MIC5021BN
–40°C to +85°C
8-pin Plastic DIP
Typical Application
+12V to +36V
MIC5021
10µF
TTL Input
1
2
3
optional*
4
VDD
Input
VBOOST
Gate
CT
Sense
Gnd
Sense
8
7
N-Channel
Power MOSFET
6
5
2.7
nF
Load
RSENSE
RSENSE = 50mV
ITRIP
* increases time before retry
High-Side Driver with Overcurrent Trip and Retry
October 1998
5
Part Number
5-169
MIC5021
Micrel
Pin Configuration
VBOOST 8
1
VDD
Gate 7
2
Input
3 CT
Sense− 6
3
CT
4 Gnd
Sense+ 5
4
Gnd Sense+ 5
1 VDD
2 Input
DIP Package
(N)
Block Diagram
VBOOST 8
Gate 7
Sense− 6
SOIC Package
(M)
6V Internal Regulator
I1
Fault
CT
CINT
2I1
VDD
Normal
CHARGE
PUMP
Q1
Sense +
VBOOST
15V
Sense –
ON
50mV
OFF
↑ ONE↓ SHOT
Input
10I2
I2
6V
Gate
Transistor: 106
Pin Description
Pin Number
Pin Name
Pin Function
1
VDD
Supply: +12V to +36V. Decouple with ≥ 10µF capacitor.
2
Input
TTL Compatible Input: Logic high turns the external MOSFET on. An
internal pull-down returns an open pin to logic low.
3
CT
4
Gnd
5
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
Sense –
Current Sense Comparator (–) Input: Connect to the low side of the sense
resistor (usually the high side of the load).
7
Gate
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.
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.
Circuit Ground
5-170
October 1998
MIC5021
Micrel
Absolute Maximum Ratings
Operating Ratings
Supply Voltage (VDD) .................................................. +40V
Input Voltage ................................................ –0.5V to +15V
Sense Differential Voltage .......................................... ±6.5V
Sense + or Sense – to Gnd .......................... –0.5V to +36V
Timer Voltage (CT) ..................................................... +5.5V
VBOOST Capacitor .................................................... 0.01µF
Supply Voltage (VDD) .................................... +12V to +36V
Temperature Range
PDIP ....................................................... –40°C to +85°C
SOIC ...................................................... –40°C to +85°C
Electrical Characteristics
TA = 25°C, Gnd = 0V, VDD = 12V, CT = Open, Gate CL = 1500pF (IRF540 MOSFET) unless otherwise specified
Symbol
Parameter
Condition
D.C. Supply Current
Min
Typ
Max
Units
VDD = 12V, Input = 0V
1.8
4
mA
VDD = 36V, Input = 0V
2.5
6
mA
VDD = 12V, Input = 5V
1.7
4
mA
VDD = 36V, Input = 5V
2.5
6
mA
1.4
2.0
V
Input Threshold
0.8
Input Hysteresis
0.1
V
Input Pull-Down Current
Input = 5V
10
20
40
µA
Current Limit Threshold
Note 1
30
50
70
mV
Gate On Voltage
VDD = 12V Note 2
16
18
21
V
VDD = 36V Note 2
46
50
52
V
tG(ON)
Gate On Time, Fixed
Sense Differential > 70mV
2
6
10
µs
tG(OFF)
Gate Off Time, Adjustable
Sense Differential > 70mV, CT = 0pF
10
20
50
µs
tDLH
Gate Turn-On Delay
Note 3
500
1000
ns
tR
Gate Rise Time
Note 4
400
500
ns
tDLH
Gate Turn-Off Delay
Note 5
800
1500
ns
tF
Gate Fall Time
Note 6
400
500
ns
fmax
Maximum Operating Frequency
Note 7
100
150
kHz
Note 1
When using sense MOSFETs, it is recommended that RSENSE < 50Ω. 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.
October 1998
5-171
5
MIC5021
Micrel
Typical Characteristics
Gate Voltage Change
vs. Supply Voltage
Supply Current vs.
Supply Voltage
2.5
Gate Turn-On Delay vs.
Supply Voltage
900
25
VGATE = VSUPPLY + 4V
CL = 1500pF (IRCZ34)
CBOOST = 0.01µF
VGATE = VGATE – VSUPPLY
VIN = 0V
VIN = 5V
1.0
tON 4V (ns)
1.5
850
20
VGATE (V)
ISUPPLY (mA)
2.0
15
10
800
750
INCLUDES PROPAGATION DELAY
5
0.5
0.0
5
10
15
20 25 30
VSUPPLY (V)
35
0
40
700
5
1000
35
650
40
850
2000
1750
1.5
0.5
15
20 25 30
VSUPPLY (V)
35
Overcurrent Retry Duty
Cycle vs. Timing Capacitance
5
0
0.1
NOTE:
tON, tOFF TIME
INDEPENDENT
OF VSUPPLY
1
60
40
20
10
100
CT (pF)
0
1000 10000
Input
Gate
Sense +, –
Differential
10
15
20 25 30
VSUPPLY (V)
35
40
70
80
IIN (µA)
10
CGATE = 1500pF
(IRCZ34)
80
VSUPPLY = 12V
15
RL = 400
Sense Threshold vs.
Temperature
VOLTAGE (mV)
20
750
5
Input Current vs.
Input Voltage
100
tON = 5µs
VSUPPLY = 12V
40
INCLUDES PROPAGATION DELAY
0.0
1x100 1x101 1x102 1x103 1x104 1x105
CGATE (pF)
25
35
1000
INCLUDES PROPAGATION DELAY
40
20 25 30
VSUPPLY (V)
VGATE = VSUPPLY + 4V
1250
INCLUDES PROPAGATION DELAY
10
15
1500
1.0
800
10
tOFF 4V (ns)
900
5
5
Gate Turn-Off Delay vs.
Supply Voltage
VGATE = VSUPPLY + 4V
VSUPPLY = 12V
2.0
tON (µs)
tON 10V (ns)
20 25 30
VSUPPLY (V)
2.5
VGATE = VSUPPLY + 10V
CL = 1500pF (IRCZ34)
CBOOST = 0.01µF
950
RETRY DUTY CYCLE (%)
15
Gate Turn-On Delay vs.
Gate Capacitance
Gate Turn-On Delay vs.
Supply Voltage
750
10
60
50
40
30
0
5
10
15
VIN (V)
20
20
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
25
TTL (H)
0V
15V (max.)
Source
50mV
0V
Timing Diagram 1. Normal Operation
6µs
Input
Gate
Sense +, –
Differential
20µs
6µs
TTL (H)
Input
0V
15V (max.)
Gate
Source
Sense +, –
Differential
50mV
0V
Timing Diagram 2. Fault Condition, CT = Open
TTL (H)
0V
15V (max.)
Source
50mV
0V
Timing Diagram 3. Fault Condition, CT = Grounded
5-172
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 (10I2) 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 VBOOST 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 VBOOST pin
voltage. The boost capacitor charge is directed through the
GATE pin to quickly charge the MOSFET’s gate to 16V
maximum above VDD. The internal charge pump maintains
the gate voltage.
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 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.
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 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
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 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.
Overcurrent Limiting
Current source I1 charges CINT upon power up. An optional
external capacitor connected to CT is kept discharged through
a MOSFET Q1.
A fault condition (> 50mV from SENSE + to SENSE –) causes
the overcurrent comparator to enable current sink 2I1 which
overcomes current source I1 to discharge CINT in a short time.
When CINT is discharged, the INPUT is disabled, which turns
off the gate output, and CINT and CT 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 2I1. This allows CINT and the optional capacitor
connected to CT to recharge. A Schmitt trigger delays the
retry while the capacitor(s) recharge. Retry delay is increased by connecting a capacitor to CT (optional).
The retry cycle will continue until the fault is removed or the
input is changed to TTL low.
If CT is connected to ground, the circuit will not retry upon a
fault condition.
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 logiclevel 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 capacitor a more significant
voltage supply than the internal charge pump.
5-173
5
MIC5021
Micrel
A 0.01µF boost capacitor is recommended for best performance in the 12V to 20V range. Refer to figure 1. Larger
capacitors may damage the MIC5021.
+12V to +36V
MIC5021
10µF
TTL Input
1
2
3
4
VDD
Input
CT
VBOOST
Gate
Sense
Gnd
Sense
8
7
6
5
2.7
nF
Load
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-tosource 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.
Overcurrent Limiting
A 50mV 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 heating elements, and
can be adjusted from the CT connection.
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” 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 CT exceeds the absolute
maximum voltage rating.
Boost Capacitor Selection
The boost capacitor value will vary depending on the supply
voltage range.
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 VDD and VBOOST as
shown in Figure 3.
+12V to +36V
MIC5021
10µF
TTL Input
1
2
3
4
Input
VBOOST
Gate
CT
Sense
Gnd
Sense
0.1
µF
7
6
5
Load
+12V to +20V
VDD
8
MIC5021
10µF
TTL Input
1
2
3
Input
CT
Gnd
VBOOST
Gate
Sense
Sense
8
7
6
5
0.01
µF
Load
4
VDD
Figure 3. Preferred 20V to 36V Configuration
Do not use both boost capacitor between VBOOST and the
MOSFET source and VBOOST and VDD at the same time.
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 resistors. 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
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.
V+
MIC5021
10µF
TTL Input
1
2
3
4
VDD
Input
VBOOST
Gate
CT
Sense−
Gnd
Sense+
8
+20V to +36V
7
6
5
(+24V)
N-Channel
Power MOSFET
MIC5021
1
10µF
0.01
µF
2
TTL Input
Load
3
4
Figure 4a. Connecting Sense to Source
VDD
VBOOST
Input
Gate
CT
Sense
Gnd
Sense
8
0.01
µF
7
N-Channel
Power MOSFET
(IRF540)
6
5
RSENSE
(< 0.08Ω)
V+
Solenoid
(24V, 47Ω)
MIC5021
10µF
TTL Input
1
2
3
4
VDD
Input
CT
Gnd
VBOOST
Gate
Sense−
Sense+
8
7
N-Channel
Power MOSFET
6
5
0.01
µF
Load
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 attempts 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.
October 1998
Schottky
Diode
(1N5822)
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 effectively reverses the supply voltage on portions of the driver
resulting in unpredictable operation or damage.
MIC5021
1
2
3
4
8
VDD
Input
CT
Gate
5
7
6
MOSFET
Turnoff
~VDD
5
0V
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.
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 resistive loads. Because of their small size, the diodes’ forward
voltage drop quickly exceeds 0.5V as current increases.
5-175
MIC5021
Micrel
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.
High-Side Sensing
Sensing the current on the high side of the MOSFET isolates
the SENSE pins from the inductive spike.
+12V to +20V
(+12V)
MIC5021
1
2
3
4
VDD
Input
Sense−
Gnd
Sense+
N-Channel
Power MOSFET
6
5
3
4
TTL Input
3
4
Input
VBOOST
Gate
CT
Sense
Gnd
Sense
CT
Sense
Gnd
Sense
10µF
1
2
3
7
4
D2
11DQ03
5
(+12V)
8
5
N-Channel
Power MOSFET
(IRFZ44)
6
V+
TTL Input
6
7
Figure 9. High Side Sensing
Lamp Driver Application
Incandescent lamps have a high inrush current (low resistance) 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.
MIC5021
VDD
Gate
Wirewound
Resistor
(3Ω)
+12V to +36V
2
Input
RSENSE
(< 0.01Ω)
8
0.01
µF
Figure 7. Resistor Voltage Drop
During normal operation, sensing current from the sense pins
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 voltages 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.
10µF
VBOOST
Load
15µA
VR2
VDD
RS 50mV nominal
(at trip)
R1 ≅ 3 × R2
1
2
TTL Input
R1
5µA
VR1
R2
VR1 = VR2
to avoid skewing
the 50mV trip point..
(5mV suggested)
1
10µF
7
Gate
CT
MIC5021
8
VBOOST
2.7
nF
R1
N-Channel
Power MOSFET
MIC5021
VDD
Input
VBOOST
Gate
CT
Sense−
Gnd
Sense+
8
7
N-Channel
Power MOSFET
(IRF540)
6
5
0.01
µF
RSENSE
(0.041Ω)
1.0k
"( )" values apply to demo circuit.
See text.
RSENSE
Incandescent
Lamp (#1157)
R2
D3
11DQ03
330Ω
D1
Inductive
Load
Figure 8. Protection from Inductive Kick
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 RS shown in Figure 10 allows
for soft start of the higher-resistance filament (measures
approx. 2.1Ω cold or 21Ω hot).
5-176
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
CT pin can be used to reset the MIC5021.
+12V to +36V
MIC5021AJB
10µF
2
TTL Input
+12V to +20V
1
3
4
MIC5021
74HC04
(example)
2
3
VDD
Input
CT
2N3904
4
Q1
Gnd
VBOOST
Gate
Sense
Sense
N-Channel
Power
MOSFET
6
Sense
Gnd
Sense
6
2.7
nF
5
2.2M
add resistor for
–40°C to –55°C
operation
0.01
µF
RSENSE
Retry (H)
Maintained (L)
Load
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
Switching Q1 on pulls CT low which keeps the MIC5021 GATE
output off when an overcurrent is sensed. Switching Q1 off
causes CT to appear open. The MIC5021 retries in about
20µs and continues to retry until the overcurrent condition is
removed.
For demonstration purposes, a 680Ω load resistor and 3Ω
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 temperature range version—no longer available) approaches –55°C,
the driver’s off-state, gate-output offset from ground increases. 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.
October 1998
CT
7
RSENSE
7
5
Gate
8
Load
TTL Input
10k to
100k
8
Input
VBOOST
+12V to +36V
MIC5021AJB
10µF
TTL Input
1
2
3
4
VDD
Input
VBOOST
Gate
CT
Sense
Gnd
Sense
8
7
6
5
2.7
nF
RSENSE
add resistor for
–40°C to –55°C
operation
2.2M
Load
10µF
1
VDD
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.
5-177
5
Similar pages