View MIC5010_31752.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

MIC5010
Micrel
MIC5010
Full-Featured High- or Low-Side MOSFET Driver Not Recommended for New Designs
General Description
The MIC5010 is the full-featured member of the Micrel MIC501X driver family. These ICs are designed to drive the gate of an N-channel power MOSFET above the supply rail in high-side power switch applications. The MIC5010 is compatible with standard or current-sensing power FETs in both high- and low-side driver topologies. The MIC5010 charges a 1nF load in 60s typical and protects the MOSFET from over-current conditions. Faster switching is achieved by adding two 1nF charge pump capacitors. 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 MIC5010 has turned off the FET due to excessive current. Other members of the Micrel driver family include the MIC5011 minimum parts count 8 pin driver, MIC5012 dual driver, and MIC5013 protected 8 pin driver.
Features
* 7V to 32V operation * Less than 1A standby current in the "OFF" state * Internal charge pump to drive the gate of an N-channel power FET above supply * Available in small outline SOIC packages * Internal zener clamp for gate protection * 25s 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 Half or full H-bridge drivers
5
Package 14-pin Plastic DIP 14-pin SOIC
Typical Application
Ordering Information
Part Number MIC5010BN MIC5010BM Temperature Range -40C to +85C -40C to +85C
MIC5010
1 Inhibit 2 NC Control Input RTH 20k 3 Input 4 Thresh 5 Sense 6 Source 7 Gnd Fault 14 V+ 13 NC 12 C1 11 Com 10 C2 9 Gate 8
V+ =24V
+ 10F R=
S
SR( V
TRIP
+100mV) +100mV)
R IL - ( V
TRIP
IRCZ44 (S=2590, R=11m)
SENSE
R1=
V+SRRS 100mV (SR+R S)
RS 43
SOURCE
R TH =
2200 V
TRIP
-1000
LOAD
Note: The MIC5010 is ESD sensitive.
KELVIN
R1 4.3k
For this example: I =30A (trip current)
L
V
TRIP
=100mV
Figure 1. High-Side Driver with Current-Sensing MOSFET
Protected under one or more of the following Micrel patents: patent #4,951,101; patent #4,914,546
April 1998
5-87
MIC5010
Micrel
Absolute Maximum Ratings (Note 1, 2)
Inhibit Voltage, Pin 1 Input Voltage, Pin 3 Threshold Voltage, Pin 4 Sense Voltage, Pin 5 Source Voltage, Pin 6 Current into Pin 6 Gate Voltage, Pin 8 Supply Voltage (V+), Pin 13 Fault Output Current, Pin 14 Junction Temperature -1V to V+ -10V to V+ - 0.5 to +5V -10V to V+ -10V to V+ 50 mA -1V to 50V -0.5V to 36V -1mA to +1mA 150C
Operating Ratings (Notes 1, 2)
Power Dissipation JA (Plastic DIP) JA (SOIC) Ambient Temperature: B version Storage Temperature Lead Temperature (Soldering, 10 seconds) Supply Voltage (V+), Pin 13 1.56W 80 C/W 115C/W -40C to +85C -65C to +150C 260C 7V to 32V high side 7V to 15V low side
Pin Description (Refer to Figures 1 and 2)
Pin Number 1 3 4 Pin Name Inhibit Input Threshold Pin Function Inhibits current sense function when connected to supply. Normally grounded. Resets current sense latch and turns on power MOSFET when taken above threshold (3.5V typical). Pin 3 requires <1A to switch. Sets current sense trip voltage according to:
VTRIP =
2200 R TH +1000
where RTH to ground is 3.3k to 20k. Adding capacitor CTH increases the trip voltage at turn-on to 2V. Use CTH =10F for a 10mS turn-on time constant. 5 Sense The sense pin causes the current sense to trip when VSENSE is VTRIP above VSOURCE. Pin 5 is used in conjunction with a current shunt in the source of a 3 lead FET or a resistor RS in the sense lead of a current sensing FET. Reference for the current sense voltage on pin 5 and return for the gate clamp zener. Connect to the load side of current shunt or kelvin lead of current sensing FET. Pins 5 and 6 can safely swing to -10V when turning off inductive loads.
6
Source
7 8 9, 10, 11 13 14
Ground Gate C2, Com, C1 V+ Fault Drives and clamps the gate of the power FET. Pin 8 will be clamped to approximately -0.7V by an internal diode when turning off inductive loads. Optional 1nF capacitors reduce gate turn-on time; C2 has dominant effect. Supply pin; must be decoupled to isolate from large transients caused by the power FET drain. 10F is recommended close to pins 13 and 7. Outputs status of protection circuit when pin 3 is high. Fault low indicates normal operation; fault high indicates current sense tripped.
Pin Configuration
MIC5010
1 2 3 4 5 6 7 Inhibit Fault NC Input Thresh V+ NC C1 14 13 12 11 10 9 8
Sense Com Source Gnd C2 Gate
5-88
April 1998
MIC5010
Micrel
Electrical Characteristics (Note 3) Test circuit. TA = -55C to +125C, V+ = 15V, V1 = 0 V, I4 = I5 = I14 = 0, all
switches open, unless otherwise specified.
Parameter Supply Current, I13 Logic Input Voltage, VIN Conditions V+ = 32V VIN = 0V, S4 closed VIN = VS = 32V, I4 = 200A V+ = 4.75V Adjust VIN for VGATE low Adjust VIN for VGATE high V+ Logic Input Current, I3 Input Capacitance Gate Drive, VGATE Zener Clamp, VGATE - VSOURCE Gate Turn-on Time, tON (Note 4) Gate Turn-off Time, tOFF Threshold Bias Voltage, V4 Current Sense Trip Voltage, VSENSE - VSOURCE = 15V Adjust VIN for VGATE high VIN = 0V VIN = 32V Pin 3 S1, S2 closed, VS = V+, VIN = 5V S2 closed, VIN = 5V V+ V+ = 7V, I8 = 0 = 15V, I8 = 100 A = 32V, VS = 32V 13 24 11 11 5 15 27 12.5 13 25 4 1.7 V+ = 7V, S4 closed VS = 4.9V S4 closed VS = 11.8V VS = 0V VS = 25.5V 75 70 150 140 360 350 1.6 I4 = 100 A V+ = 15V I4 = 200 A V+ = 32V I4 = 500 A Peak Current Trip Voltage, VSENSE - VSOURCE Fault Output Voltage, V14 Current Sense Inhibit, V1 S3, S4 closed, V+ = 15V, VIN = 5V VIN = 0V, I14 = -100 A VIN = 5V, I14 = 100 A, current sense tripped V1 above which current sense is disabled Minimum possible V1
Note 1 Note 2 Note 3 Note 4
Min
Typical 0.1 8
Max 10 20 2
Units A mA V V V A A pF V V
4.5 5.0 -1 1
V+ = 32V
V+ = 15V, VS = 15V V+
15 16 50 10 2.2 135 130 270 260 680 650
V V s s V mV mV mV mV mV mV V
VIN switched from 0 to 5V; measure time for VGATE to reach 20V VIN switched from 5 to 0V; measure time for VGATE to reach 1V I4 = 200 A S2 closed, VIN = 5V, Increase I5
2 105 100 210 200 520 500 2.1 0.4
5
1
V V
14
14.6 7.5 1 13
V V
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. The MIC5010 is ESD sensitive. Minimum and maximum Electrical Characteristics are 100% tested at TA = 25C and TA = 85C, and 100% guaranteed over the entire range. Typicals are characterized at 25C and represent the most likely parametric norm. Test conditions reflect worst case high-side driver performance. Low-side and bootstrapped topologies are significantly faster--see Applications Information.
April 1998
5-89
MIC5010
Micrel
Test Circuit
V+ + 1F I5 V1 1 2 3 V3 50 4 5 6 S3 I4 S4 S2 VS 500 1W 3.5k 7
MIC5010
Inhibit Fault NC Input Thresh V+ NC C1 14 13 12 11 10 9 8 1nF S1 I8 1nF 1nF I14
Sense Com Source Gnd C2 Gate
Typical Characteristics
Supply Current
12
DC Gate Voltage above Supply
14 12
SUPPLY CURRENT (mA)
VGATE - V+ (V)
10 8 6 4 2 0
10 8 6 4 2 0
0
5
10
15
20
25
30
35
0
3
6
9
12
15
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
5-90
April 1998
MIC5010
Micrel
Typical Characteristics (Continued)
High-side Turn-on Time*
350
140
High-side Turn-on Time*
120 100 80 60 40 20 CGATE =1 nF C2=1 nF
TURN-ON TIME (S)
250 200 150 100 50 0 0 3 6
CGATE =1 nF
TURN-ON TIME (S)
15
300
9
12
0
0
3
6
9
12
15
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
High-side Turn-on Time*
3.5
High-side Turn-on Time*
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 3 6 9 12 15 CGATE =10 nF C2=1 nF
TURN-ON TIME (mS)
2.5 2.0 1.5 1.0 0.5 0 0 3 6
CGATE =10 nF
TURN-ON TIME (mS)
3.0
5
9
12
15
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
CHARGE-PUMP CURRENT (mA)
CHARGE-PUMP CURRENT (A)
Charge Pump Output Current
250 VGATE =V+ 200 150 VGATE =V++5V 100 50 VS=V +-5V 0 0 5 10 15 20 25 30
Charge Pump Output Current
1.0 0.8 0.6 0.4 0.2 0 0 5 10 C2=1 nF VS=V +-5V 15 20 25 30 VGATE =V + +5V VGATE =V+
SUPPLY VOLTAGE (V)
* Time for gate to reach V+ + 5V in test circuit with VS = V+
SUPPLY VOLTAGE (V)
- 5V (prevents gate clamp from interfering with measurement).
April 1998
5-91
MIC5010
Micrel
Typical Characteristics (Continued)
Turn-off Time
NORMALIZED TURN-ON TIME
50
2.0 1.75 1.5 1.25 1.0 0.75 0.5 -25 0 25 50 75 100 125
Turn-on Time
TURN-OFF TIME (S)
40 30 20 10 0 0
CGATE =10 nF
CGATE =1 nF
3
6
9
12
15
SUPPLY VOLTAGE (V)
DIE TEMPERATURE (C)
Low-side Turn-on Time for Gate = 5V
1000
1000
Low-side Turn-on Time for Gate = 5V
C2=1 nF CGATE =10 nF 100 30 10 CGATE =1 nF 3 1
TURN-ON TIME (S)
300 CGATE =10 nF 100 30 10 3 1 0 3 6 9 12 15 CGATE =1 nF
TURN-ON TIME (S)
300
0
3
6
9
12
15
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
Low-side Turn-on Time for Gate = 10V
3000
3000
Low-side Turn-on Time for Gate = 10V
C2=1 nF
TURN-ON TIME (S)
TURN-ON TIME (S)
1000 300 100 30 10 3 0 CGATE =1 nF
CGATE =10 nF
1000 300 100 30 10 3 0 CGATE =1 nF CGATE =10 nF
3
6
9
12
15
3
6
9
12
15
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
5-92
April 1998
MIC5010
Micrel
A resistor RTH from pin 4 to ground sets I4, and hence VTRIP. An additional capacitor CTH from pin 4 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 14 will be high as long as the input pin 3 remains high. However, when the input is low the fault pin will also be low. Construction Hints High current pulse circuits demand equipment and assembly techniques that are more stringent than normal, low current lab practices. The following are the sources of common pitfalls encountered while prototyping:Supplies: 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 undershoot 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--especially electrolytic capacitors--with possibly catastrophic results. A 10F supply bypass capacitor at the chip is recommended.
Applications Information
Functional Description (Refer to Block Diagram) The various MIC5010 functions are controlled via a logic block connected to the input pin 3. 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 turnon 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 onchip pump capacitors capable of charging 1 nF to 5V above supply in 60S typical. With the addition of 1nF capacitors at C1 and C2, the turn-on time is reduced to 25S typical. The charge pump is capable of pumping thegate up to over twice the supply voltage. For this reason a zener clamp (12.5V typical) is provided between the gate pin 8 and the source pin 6 to prevent exceeding the VGS rating of the MOSFET at high supplies. The current sense operates by comparing the sense voltage at pin 5 to an offset version of the source voltage at pin 6. Current I4 flowing in threshold pin 4 is mirrored and returned to the source via a 1k resistor to set the offset or trip voltage. When (VSENSE - VSOURCE) exceeds VTRIP , 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 5. The latch is reset to turn the FET back on by "recycling" the input pin 3 low and then high again.
5
Block Diagram
V+ 13 C1 Com C2 11 10 9
CHARGE PUMP
500
8 Gate
Input 3
LOGIC V+
CURRENT SENSE LATCH
12.5V
MIC5010
+ I4 +
VTRIP 1k
Fault 14
Q
R S
5 Sense
TEMP SENSE
V. REG
1k
-
6 Source
7 Ground
1 Inhibit
4 Threshold
April 1998
5-93
MIC5010
Micrel
500mV (RTH = 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 (V4). The values shown in Figure 2 are designed for a trip current of 20 amperes. It is important to ground pin 6 at the current shunt RS, 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 MIC5010 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 10s 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 (RS) on top of the load. R1 and R2 add a small, additional potential to VTRIP to prevent falsetriggering 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 MIC501X drivers are
Applications Information (Continued)
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 100 m 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 under load.
Circuit Topologies The MIC5010 is suited for use in high- or low-side driver applications with over-current protection for both currentsensing and standard MOSFETs. In addition, the MIC5010 works well in applications where, for faster switching times, the supply is bootstrapped from the MOSFET source output. 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 10s to VGS = 1V). The choice of one topology over another is based on a combination of considerations including speed, voltage, and desired system characteristics. Each topology is described in this section. Note that IL, 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 overcurrent comparator monitors RS and trips if IL x RS exceeds VTRIP. RTH is selected to produce the desired trip voltage. As a guideline, keep VTRIP within the limits of 100mV and
V+=7 to 15V
V LOAD
MIC5010
1 Inhibit 2 NC Control Input RTH 10k Fault 14 V+ 13 RS= RTH = LOAD V
TRIP
3 Input NC 12 4 Thresh C1 11 5 Sense 6 Source 7 Gnd Com 10 C2 9 Gate 8
+ 10F
I
L
2200 V
TRIP
-1000
For this example: IRF540 I =20A (trip current) L VTRIP = 200mV RS 10m IRC 4LPW-5 (International Resistive Company)
Figure 2. Low-Side Driver with Current Shunt
5-94
April 1998
MIC5010
Micrel
Applications Information (Continued)
MIC5010
1 Inhibit 2 NC Control Input R
TH
Fault 14 V+ 13 NC 12 C1 11 Com 10 C2 9 Gate 8
+ V =24V R1= + 10F
V+ 1mA
3 Input 4 Thresh 5 Sense 6 Source 7 Gnd
R2=100 100mV+V IL 2200 V
TRIP
20k
RS = IRF541 100 R2 RS 18m IRC 4LPW-5* LOAD RTH =
TRIP
-1000
For this example: I L =10A (trip current) VTRIP =100mV
R1 24k
*International Resistive Company
Figure 3. High-Side Driver with Current Shunt
self-protected against inductive switching transients. During 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 MIC5010 source and sense pins (5 and 6) are designed to withstand this negative excursion without damage. External clamp diodes are unnecessary, but may be added to reduce power dissipation in the MOSFET. Current Shunts (RS). Low-valued resistors are necessary for use at RS.Values for RS range from 5 to 50m, at 2 to 10W. Worthy of special mention are Kelvin-sensed, "fourterminal" units supplied by a number of manufacturers. Kelvin-sensed resistors eliminate errors that are 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, 500ppm/C change will contribute as much as 10% shift in the overcurrent trip point. Most power resistors designed for current shunt service drift less than 100ppm/C. 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 specified 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. VTRIP must be less than R x IL, or else RS will become negative. Substituting a MOSFET with higher onresistance, or reducing VTRIP fixes this problem. VTRIP = 100 to 200mV is suggested. Although the load supply is limited only by MOSFET ratings, the MIC5010 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. RDS(ON) as specified on MOSFET data sheets 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 (RDS(ON) 100m) by simply halving the stated RDS(ON), or by subtracting 20 to 50m from the stated RDS(ON) for smaller MOSFETs. High-Side Driver with Current Sensing MOSFET (Figure 1). The design starts by determining the value of "S" and "R" for the MOSFET (use the guidelines described for the lowside version). Let VTRIP = 100 mV, and calculate RS for a desired trip current. Next calculate RTH and R1. The trip
5
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
April 1998
5-95
MIC5010
Micrel
Applications Information (Continued)
MIC5010
1 Inhibit 2 NC 3 Input 4 Thresh 5 Sense Fault 14 V+ 13 NC 12 C1 11 Com 10 LOAD + 10F R TH= RS = SR V
L TRIP TRIP
+ V =15V
V
LOAD
Control Input
R I -V 2200 V
TRIP
R TH 20k
-1000
6 Source C2 9 7 Gnd Gate 8
SENSE
IRCZ44 (S=2590, R=11m) RS 22
KELVIN
For this example: I =20A (trip current)
L
V
SOURCE
TRIP
=100mV
Figure 4. Low-Side Driver with Current-Sensing MOSFET
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. Typical Applications Start-up into a Dead Short. If the MIC5010 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 10s. 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 10s SOA, a small inductance in series with the source can help limit di/dt to control the peak current during the 5 to 10s 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 100s can be observed at the threshold of shutdown. A 20% overdrive reduces the delay to near minimum. Incandescent Lamps. The cold filament of an incandescent 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-current trip point is set to less than 70A, the MIC5010 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 MIC5010 over-current shutdown circuit is designed to handle this situation by varying the trip point with time (see Figure 5). RTH1 functions in the conventional manner, providing a current limit of approximately twice that required by the lamp. RTH2 acts to increase the current limit at turnon to approximately 10 times the steady-state lamp current. The high initial trip point decays away according to a 20ms time constant contributed by CTH. RTH2 could be eliminated with CTH 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 RTH2/CTH network to allow for lamp start-up. Let RTH2 = (RTH1 / 10) - 1k, and choose a capacitor that provides the desired time constant working against RTH2 and the internal 1k resistor. When the MIC5010 is turned off, the threshold pin (4) appears as an open circuit, and CTH is discharged through RTH1 and RTH2. This is much slower than the turn-on time
MIC5010
1 Inhibit 2 NC RTH2 1k Control Input 3 Input 4 Thresh Fault 14 V+ 13 NC 12 C1 11
12V
+ 10F
RTH1 22k
5 Sense Com 10 6 Source C2 9 7 Gnd Gate 8
IRCZ44
CTH 22F 43 3.9k #6014
Figure 5. Time-Variable Trip Threshold
5-96
April 1998
MIC5010
Micrel
In a PWM application the chip supply is actually much higher than the system supply, which improves switching time.
Applications Information (Continued)
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 CTH. Modifying Switching Times. Do not add external capacitors to the gate to slow down the switching time. Add a resistor (1k to 51k) in series with the gate of the MOSFET to achieve this result. External capacitors can be added at C1 and C2 for faster switching times (see Block Diagram). Values of 100pF to 1nF produce useful speed increases. If component count is critical, C2 (pins 9 to 10) can be used alone with only a small loss of speed compared to using both capacitors. Bootstrapped High-Side Driver (Figure 6). The speed of a high-side driver can be increased to better than 10s by bootstrapping the supply off of the MOSFET source. This topology can be used where the load is pulse-width modulated (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 MIC5010 supply pin will fall to V+ = VDD - 1.4. Under this condition pins 5 and 6 will be held above V+ and may false trigger the over-current circuit. A larger capacitor will lengthen the maximum "on" time; 1000F 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. 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 MIC5010 is turned off.
V DD =7 to 15V
MIC5010
1 Inhibit 2 NC Control Input 3 Input 4 Thresh Fault 14 V+ 13 1N5817 1N4001 (2) + 10F
100nF NC 12 C1 11
20k 5 Sense Com 10 6 Source C2 9 7 Gnd Gate 8 100
IRF540
18m + R1= V 1mA
LOAD
Figure 6. Bootstrapped High-Side Driver
Electronic Circuit Breaker (Figure 7). The MIC5010 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
5
12V
12V
100k 100k 100nF
100k
MIC5010
10k MPSA05 20k 1 Inhibit 2 NC 3 Input 4 Thresh Fault 14 V+ 13 NC 12 C1 11
+ 10F
5 Sense Com 10 6 Source C2 9 7 Gnd Gate 8 100
IRFZ40
1N4148
22m CPSL-3 (Dale) 10k LOAD
Figure 7. 10-Ampere Electronic Circuit Breaker
April 1998 5-97
MIC5010
Micrel
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 precedence. 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 distributes the switch dissipation into multiple packages. High-Voltage Bootstrap (Figure 10). Although the MIC5010 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 MIC5010 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 MIC5010 is supplied by a charge pump. A 20kHz square wave (15Vp-p) drives the pump capacitor and delivers current to a 100F storage capacitor. A zener diode limits the supply to 18V. When the MIC5010 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 dissipation and, in the case of the MIC5010, could trip the overcurrent 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 3s dead time effectively eliminating
24V
Applications Information (Continued)
15V 33k 33pF 100k MPSA05 10mA Control Input 4N35 100k 1k To MIC5010 Input
Figure 8. Improved Opto-Isolator Performance
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 MIC5010 has no special input slew rate requirement, the lethargic transitions provided by an opto-isolator may cause oscillations 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 MIC5010 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 MIC5010 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
24V
MIC5010
100k ON CR2943-NA102A (GE) OFF 20k 1 Inhibit 2 NC 3 Input 4 Thresh 5 Sense 6 Source 7 Gnd Fault 14 V+ 13 NC 12 C1 11 Com 10 C2 9 Gate 8 100 5m 330k 15k LVF-15 (RCD) LOAD
+ 10F
IRFP044 (2)
Figure 9. 50-Ampere Industrial Switch
5-98 April 1998
MIC5010
Micrel
Applications Information (Continued)
15V
1N4003 (2) 1 33k 33pF 100k 4N35 100k
MIC5010
Inhibit 2 NC 3 NC 12 Input MPSA05 4 C1 11 Thresh 6.2k 5 Sense Com 10 6 C2 9 Source 7 Gnd Gate 8 Fault 14 V+ 13 1N4746 + 100F 90V 1nF IRFP250
10mA Control Input
1k
10m KC1000-4T (Kelvin) 1/4 HP, 90V 5BPB56HAA100 (GE)
100nF 200V 15Vp-p, 20kHz Squarewave
1N4003
M
Figure 10. High-Voltage Bootstrapped Driver
cross conduction. Both the top- and bottom-side drivers are protected, so the output can be shorted to either rail without damage. The top-side driver is based on the bootstrapped circuit of Figure 6, and cannot be switched on indefinitely. The bootstrap capacitor (1F) 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 Hbridge 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 22m current-sensing resistor. Time-Delay Relay (Figure 12). The MIC5010 forms the basis of a simple time-delay relay. As shown, the delay commences when power is applied, but the 100k/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 3 to ground. Motor Driver with Stall Shutdown (Figure 13). Tachometer 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 MIC5010 input ON. If the motor slows down, the tach output is reduced, and the MIC5010 switches OFF. Resistor "R" sets the shutdown threshold. If the output current exceeds 30A, the MIC5010 shuts down and remains in that condition until the momentary "RESET" button is pushed. Control is then returned to the START/RUN/STOP switch.
5
April 1998
5-99
MIC5010
Micrel
Applications Information (Continued)
15V
MIC5010
1N4148 1 Inhibit 2 NC 220pF 20k 3 Input 4 Thresh 5 Sense 6 Source 7 Gnd Fault 14 V+ 13 C1 11 Com 10 C2 9 Gate 8
1N5817 1N4001 (2) + 1F
100nF NC 12
22k
IRF541 100 22m CPSL-3 (Dale) 15k
PWM INPUT
15V
M 10A Stalled MIC5010
1 Inhibit 2 NC 3 Input 4 Thresh 10k 2N3904 5 Sense 6 Source 7 Gnd Fault 14 V+ 13 NC 12 C1 11 Com 10 C2 9 Gate 8 + 10F
12V,
10k 22k 1nF
IRF541 22m CPSL-3 (Dale)
Figure 11. Half-Bridge Motor Driver
5-100
April 1998
MIC5010
Micrel
Applications Information (Continued)
MIC5010
1 Inhibit 2 NC 1N4148 3 Input 4 Thresh 5 Sense Fault 14 V+ 13 NC 12 C1 11 Com 10
12V
100k
+ 10F
20k
6 Source C2 9 7 Gnd Gate 8 100F + 10k 100
IRCZ44 OUTPUT (Delay=5S) 43 4.3k
Figure 12. Time-Delay Relay with 30A Over-Current Protection
1N4148 RESET
330k
5
12V
MIC5010
1 Inhibit 2 NC 330k 20k 3 Input 4 Thresh Fault 14 V+ 13 NC 12 C1 11
+ 10F
R 330k
5 Sense Com 10 6 Source C2 9 7 Gnd Gate 8
IRCZ44
43 1N4148 100nF 4.3k
T
12V START RUN STOP
M
Figure 13. Motor Stall Shutdown
April 1998
5-101
MIC5010
Micrel
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 MIC5010 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 lowside drivers since the chip supply is boosted well above the drain at turn-on.
Applications Information (Continued)
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 MOSFET off. Q6 is turned off when the MIC5010 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
V
+
Q3 Q1 125pF C1 C1 100 kHz OSCILLATOR OFF ON Q2 Q4 COM C2 125pF C2
Q5
G 500 GATE CLAMP ZENER
12.5V
Q6 S
Figure 14. Gate Control Circuit Detail
5-102
April 1998

▲Up To Search▲

Price & Availability of MIC5010

	To Download MIC5010 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .