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MIC5020
Datasheet (MICREL)
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Datasheet MIC5020 Datasheet (MICREL)

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Page 1
MIC5020 Micrel
MIC5020
Current-Sensing Low-Side MOSFET Driver
General Description
The MIC5020 low-side MOSFET driver is designed to oper­ate at frequencies greater than 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 MIC5020 can also operate as a circuit breaker with or without automatic retry. The MIC5020’s maximum supply voltage lends itself to control applications using up to 50V. The MIC5020 can control MOSFETs that switch voltages greater than 50V.
A rising or falling edge on the input results in a current source or sink pulse on the gate output. This output current pulse can turn on or off a 2000pF MOSFET in approximately 175ns. The MIC5020 then supplies a limited current (< 2mA), if necessary, to maintain the output state.
An overcurrent comparator with a trip voltage of 50mV makes the MIC5020 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 connected to the CT pin may be used to control the current shutdown duty cycle from 20% to < 1%. A duty cycle from 20% to about 75% is possible with an optional pull-up resistor from CT to VDD. An open collector output provides a fault indication when the sense inputs are tripped.
The MIC5020 is available in 8-pin SOIC and plastic DIP packages.
Other members of the MIC502x series include the MIC5021 high-side driver and the MIC5022 half-bridge driver with a cross-conduction interlock.
Features
• 11V to 50V operation
• 175ns rise/fall time driving 2000pF
• TTL compatible input with internal pull-down resistor
• Overcurrent limit
• Fault output indication
• Gate to source protection
• Compatible with current sensing MOSFETs
Applications
• Lamp control
• Heater control
• Motor control
• Solenoid switching
• Switch-mode power supplies
• Circuit breaker
Ordering Information
Part Number Temperature Range Package
MIC5020BM –40°C to +85°C 8-pin SOIC MIC5020BN –40°C to +85°C 8-pin Plastic DIP
Typical Application
+11V to +50V
150kHz max.
V+
Load
MIC5020
10µF
optional*
1 2 3 4
V
DD
Input Fault C
T
Sense− Sense+
Gate
Gnd
8 7 6 5
N-Channel Power MOSFET
R
SENSE
* increases time before retry
Low-Side Driver with Overcurrent Trip and Retry
5-162 October 1998
R
SENSE
=
50mV
I
TRIP
Page 2
MIC5020 Micrel
Pin Configuration
Block Diagram
Sense + Sense –
Input
1
V
DD
Input
2
Fault
3
C
4
T
DIP Package SOIC Package
6V Internal Regulator
I
1
C
INT
2I
1
50mV
8
Gate Sense− Sense+
Gnd
7 6
5
1
V
DD
Input
2 3
4
Fault C
T
Sense− Sense+
(N) (M)
Fault
Normal
Q1
↑ ↓
ONE-
SHOT
10I
2
Gate
Gnd
I
2
8 7 6
5
C
T
Fault
V
DD
ON
OFF
6V
Gate
Transistor Count: 82
Pin Description
Pin Number Pin Name Pin Function
1V 2 Input TTL Compatible Input: Logic high turns the external MOSFET on. An internal
3 Fault Overcurrent Fault Indicator: When the sense voltage exceeds threshold,
4C
5 Gnd Circuit Ground 6 Sense + Current Sense Comparator (+) Input: Connect to high side of sense resistor
7 Sense – Current Sense Comparator (–) Input: Connect to the low side of the sense
8 Gate Gate Drive: Drives the gate of an external power MOSFET. Also limits V
DD
T
Supply: +11V to +50V. Decouple with ≥ 10µF capacitor.
pull-down returns an open pin to logic low.
open collector output is open circuit for 5µs (t t
G(OFF)
. t
is adjustable from CT.
G(OFF)
Retry Timing Capacitor: Controls the off time (t retry cycle. (Duty cycle adjustment.)
), then pulled low for
G(ON)
) of the overcurrent
G(OFF)
• Open = 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.
or current sensing MOSFET sense lead. A built-in offset in conjunction with R
sets the load overcurrent trip point.
SENSE
resistor (usually power ground).
to 15V max. to prevent Gate to Source damage. Will sink and source
GS
current.
5
October 1998 5-163
Page 3
MIC5020 Micrel
Absolute Maximum Ratings
Supply Voltage (VDD) ..................................................+55V
Sense Differential Voltage..........................................±6.5V
Sense + or Sense – to Gnd.......................... –0.5V to +50V
Operating Ratings
Supply Voltage (VDD) ....................................+11V to +50V
Temperature Range
SOIC ...................................................... –40°C to +85°C
Plastic DIP..............................................–40°C to +85°C
Fault Voltage ...............................................................+50V
Timer Voltage (CT) .....................................................+5.5V
Electrical Characteristics
TA = 25°C, Gnd = 0V, VDD = 12V, Sense +,– = 0V, Fault = Open, CT = Open, Gate CL = 1500pF unless otherwise specificed
Symbol Parameter Condition Min Typ Max Units
D.C. Supply Current VDD = 12V, Input = 0V 0.8 2 mA
VDD = 50V, Input = 0V 2 10 mA VDD = 12V, Input = 5V 0.8 2 mA
VDD = 50V, Input = 5V 4 25 mA Input Threshold 0.8 1.4 2.0 V Input Hysteresis 0.1 V Input Pull-Down Current Input = 5V 10 20 40 µA Fault Output Fault Current = 1.6mA 0.15 0.4 V
Saturation Voltage Note 1 Fault Output Leakage Fault = 50V –1 0.01 +1 µA Current Limit Threshold Note 2 30 50 70 mV Gate On Voltage VDD = 12V 10 11 V
VDD = 50V 14 15 18 V
t
G(ON)
t
G(OFF)
t
DLH
t
R
t
DLH
t
F
f
max
Note 1 Voltage remains low for time affected by CT. Note 2 When using sense MOSFETs, it is recommended that R 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 10V. Note 5 Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 11V (Gate ON voltage) to 10V. Note 6 Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 10V from 2V. Note 7 Frequency where gate on voltage reduces to 10V with 50% input duty cycle.
Gate On Time, Fixed Sense Differential > 70mV 2 5 10 µs Gate Off Time, Adjustable Sense Differential > 70mV, CT = 0pF 10 20 50 µs Gate Turn-On Delay Note 3 400 800 ns Gate Rise Time Note 4 700 1500 ns Gate Turn-Off Delay Note 5 900 1500 ns Gate Fall Time Note 6 500 1500 ns Maximum Operating Frequency Note 7 100 150 kHz
< 50Ω. Higher values may affect the sense MOSFET’s current transfer ratio.
SENSE
5-164 October 1998
Page 4
MIC5020 Micrel
200
400
600
800
1000
1200
1x10
2
1x10
3
1x10
4
1x10
5
t
ON
(ns)
C
GATE
(pF)
0.0
5.0
10.0
15.0
20.0
25.0
0.1 1 10 100 1000 10000
Shutdown Duty Cycle (%)
CT (pF)
400
500
600
700
800
900
5 101520253035404550
t
ON
(nS)
V
SUPPLY
(V)
Typical Characteristics
Supply Current vs.
3.5
3.0
2.5
(mA)
2.0
SUPPLY
1.5
I
1.0
0.5
Supply Voltage
VIN = 5V
VIN = 0V
5 101520253035404550
V
SUPPLY
(V)
Input Current vs.
100
(µA) I
80
60
IN
40
20
0
Input Voltage
V
SUPPLY
0 5 10 15 20 25
VIN (V)
= 12V
Turn-On Time vs.
Supply Voltage
V
= 4V
GATE
= 1500pF
C
L
= 0 to 5V Sq. Wave
V
IN
INCLUDES PROPAGATION DELAY
Turn-On Time vs.
Gate Capacitance
V
= 4V
GATE
INCLUDES PROPAGATION DELAY
Turn-Off Time vs.
1200
1100
1000
(ns)
OFF
t
900
800
700
Supply Voltage
V
= 4V
GATE
= 1500pF
C
L
= 0 to 5V
V
IN
Sq. Wave
INCLUDES PROPAGATION DELAY
5 1015202530
V
SUPPLY
(V)
Overcurrent Shutdown
Retry Duty Cycle
tON = 5µs V
SUPPLY
= 12V
5
Sense Threshold vs.
80
70
60
50
40
VOLTAGE (mV)
30
20
-60 -30 0 30 60 90 120 150
Input
Gate
Sense +, –
Differential
Fault
Timing Diagram 2. Fault Condition, CT = Open Timing Diagram 3. Fault Condition, CT = Grounded
October 1998 5-165
Temperature
TEMPERATURE (°C)
5µs
TTL (H)
0V
15V (max.)
0V
50mV
0V
Off On
20µs
Input
Gate
Sense +, –
Differential
Fault
TTL (H)
0V
15V (max.)
0V
50mV
0V Off On
Timing Diagram 1. Normal Operation
5µs
0V
0V
0V Off On
Input
Gate
Sense +, –
Differential
Fault
TTL (H)
15V (max.)
50mV
Page 5
MIC5020 Micrel
Functional Description
Refer to the MIC5020 block diagram.
Input
A signal greater than 1.4V (nominal) applied to the MIC5020
INPUT causes gate enhancement on an external MOSFET
turning the external 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 through 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 15V Zener diode protects the external MOSFET by limiting the gate output voltage when VDD is connected to higher voltages.
Overcurrent Limiting
Current source I1 charges C
upon power up. An optional
INT
external capacitor connected to CT is discharged through
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 C When C
is discharged, the INPUT is disabled, which turns
INT
off the GATE output; the FAULT output is enabled; and C
in a short time.
INT
INT
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 C
and the optional capacitor
INT
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 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.
Fault Output
The FAULT output is an open collector transistor. FAULT is active at approximately the same time the output is disabled by a fault condition (5µs after an overcurrent condition is sensed). The FAULT output is open circuit (off) during each successive retry (5µs).
Applications Information
The MIC5020 MOSFET driver is intended for low-side switch­ing applications where higher supply voltage, overcurrent sensing, and moderate speed are required.
Supply Voltage
A feature of the MIC5020 is that its supply voltage rating of up to 50V is higher than many other low-side drivers.
The minimum supply voltage required to fully enhance an N­channel MOSFET is 11V.
A lower supply voltage may be used with logic level MOSFETs. Approximately 6V is needed to provide 5V of gate enhance­ment.
Low-Side Switch Circuit Advantages
A moderate-speed low-side driver is generally much faster than a comparable high-side driver. The MIC5020 can provide the gate drive switching times and low propagation delay times that are necessary for high-frequency high­efficiency 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) can benefit from the MIC5020’s fast switching times by allowing use of MOSFETs with smaller safe operating areas. (Larger MOSFETs are often required when using slower drivers.)
Overcurrent Limiting
source side sensing is provided by access to both SENSE + and SENSE – comparator inputs.
The adjustable retry feature can be used to handle loads with high initial currents, such as lamps, motors, or heating elements and can be adjusted from the CT connection.
CT to ground causes maintained gate drive shutdown follow­ing overcurrent detection.
CT open, or through 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 a 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.
Circuits may become unstable at a duty cycles of about 75% or higher, depending on the conditions.
Caution: The MIC5020 may be damaged if the
voltage on CT exceeds the absolute maximum rating.
An overcurrent condition is externally signaled by an open collector (FAULT) output.
The MIC5020 may be used without current sensing by connecting SENSE + and SENSE – to ground.
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-terminal current sensing resis­tors. Four-terminal resistors are available from several manufacturers.
5-166 October 1998
Page 6
MIC5020 Micrel
V
DD
Input Fault C
T
Gate Sense− Sense+
Gnd
TTL Input
(0V/5V)
N-Channel Current Sensing Power MOSFET
V+
MIC5020
1 2 3 4
8 7 6 5
10µF
Load
R
SENSE
(10Ω)
+11V to +50V
(+13.2V)
(+13.2V, > 4.4A)
(IRCZ24)
(3Ω, > 60W)
“( )” values apply to
demo circuit. See text.
Lamp Driver Application
V+
(+11V to +12V)
Incandescent Lamp (#1157)
N-Channel Power MOSFET (IRF540)
R
SENSE
(0.041Ω)
10µF
TTL Input
(0V/5V)
demo circuit. See text.
1
V
DD
2
Input
3
Fault
4
C
T
“( )” values apply to
MIC5020
Sense− Sense+
Gate
Gnd
8 7 6 5
Figure 1. 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 1 allows for soft start of the higher-resistance filament (measures approx.
2.1Ω cold or 21Ω hot).
Solenoid Driver Application
The MIC5020 can be directly powered by the control voltage supply in typical 11Vdc through 50Vdc control applications. Current sensing has been omitted as an example.
V+
+11V to +50V
MIC5020
10µF
TTL Input
1
V
DD
2
Input
3
Fault
4
C
T
Figure 2. Solenoid Driver,
Without Current Sensing
A diode across the load protects the MOSFET from the voltage spike generated by the inductive load upon MOSFET turn off. The peak forward current rating of the diode should be greater than the load current.
October 1998 5-167
Solenoid
8
Gate
7
Sense−
6
Sense+
5
Gnd
Diode
N-Channel Power MOSFET
Current Sensing MOSFET Application
A current sensing MOSFET allows current sensing without adding additional resistance to the power switching circuit.
A current sensing MOSFET has two source connections: a “power source” for power switching and a “current source” for current sensing. The current from the current source is approximately proportional to the current through the power source, but much smaller. A current sensing ratio (I I
) is provided by the MOSFET manufacturer.
SENSE
SOURCE
Figure 3. Using a Current Sensing MOSFET
The MOSFET current source is used to develop a voltage across a sense resistor. This voltage is monitored by the MIC5020 (SENSE + and SENSE – pins) to identify an overcur­rent condition.
The value of the sense resistor can be estimated with:
R
SENSE
= (r V
TRIP
R
DS(ON)
) / (I
LOAD RDS(ON)
– V
TRIP
)
where:
R V r = manufacturer’s current sense ratio: (I R I
LOAD
= external “sense” resistor
SENSE
= 50mV (0.050V) for the MIC5020
TRIP
= manufacturer’s power source on resistance
DS(ON)
= load current (power source current)
SOURCE/ISENSE
The drain to source voltage under different fault conditions affects the behavior of the MOSFET current source; that is, the current source will respond differently to a slight over­current condition (V (where V
is approximately equal to the supply voltage).
DS(ON)
very small) than to a short circuit
DS(ON)
Adjustment of the sense resistor value by experiment starting from the above formula will provide the quickest selection of R
SENSE
.
Refer to manufacture’s data sheets and application notes for detailed information on current sensing MOSFET character­istics.
Figure 3 includes values which can be used to demonstrate circuit operation. The IRCZ24 MOSFET has a typical sense ratio of 780 and a R
of 0.10Ω. A large 3Ω wirewound
DS(ON)
load resistor will cause inductive spikes which should be suppressed using a diode (using the same configuration as figure 2).
/
5
)
Page 7
MIC5020 Micrel
+
+
Faster MOSFET Switching
The MIC5020’s GATE current can be multiplied using a pair of bipolar transistors to permit faster charging and discharg­ing of the external MOSFET’s gate.
+40V max.
Load
Gate
Gnd
2N3904 8 7 6 5
2N3906
N-Channel Power MOSFET (IRF540)
+11V to +50V
150kHz max.
10µF
1 2 3 4
MIC5020
V
DD
Input Fault C
T
Sense− Sense+
Figure 4. Faster MOSFET Switching Circuit
NPN and PNP transistors are used to respectively charge and discharge the MOSFET gate. The MIC5020 gate current is multiplied by the transistor β.
Remote Overcurrent Limiting Reset
In circuit breaker applications where the MIC5020 maintains an off condition after an overcurrent condition is sensed, the CT pin can be used to reset the MIC5020.
For test 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 MIC5020AJB (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 MIC5020AJB includes low temperatures (–40°C to –55°C), add an external
2.2MΩ resistor as shown in Figures 6a or 6b. 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.
V+
Load
11V to +50V
10µF
1 2 3 4
MIC5020
V
DD
Input Fault C
T
Gate Sense Sense
Gnd
8 7
R
2.2M
SENSE
6 5
Figure 6a. Gate-to-Source Pull Down
The gate-to-source configuration (refer to Figure 6a) is ap­propriate for resistive and inductive loads. This also causes the smallest decrease in gate output voltage.
V+
Load
+11V to +50V
Retry (H)
Maintained (L)
TTL input
74HC04
(example)
10µF
10k to
100k
Q1 2N3904
1 2 3 4
MIC5020
V
DD
Input Fault C
T
Gate Sense− Sense+
Gnd
8 7 6 5
N-Channel Power MOSFET
R
Figure 5. Remote Control Circuit
Switching Q1 on pulls CT low which keeps the MIC5020 GATE output off when an overcurrent is sensed. Switching Q1 off causes CT to appear open. The MIC5020 retries in about 20µs and continues to retry until the overcurrent condition is removed.
SENSE
V+
Load
11V to +50V
10µF
1 2 3 4
MIC5020
V
DD
Input Fault C
T
Gate Sense Sense
Gnd
8 7 6 5
2.2M
R
SENSE
Figure 6b. Gate-to-Ground Pull Down
5-168 October 1998
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