MIC5020 Micrel MIC5020 Current-Sensing Low-Side MOSFET Driver General Description Features 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. • • • • • • • 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 Load V+ +11V to +50V 10µF 150kHz max. 1 2 3 4 optional* MIC5020 VDD Gate Input Sense− Fault Sense+ CT Gnd 8 7 N-Channel Power MOSFET 6 RSENSE = 50mV I TRIP 5 RSENSE * increases time before retry Low-Side Driver with Overcurrent Trip and Retry 5-162 October 1998 MIC5020 Micrel Pin Configuration 1 VDD Gate 8 1 VDD 2 Input Sense− 7 2 Input Sense− 7 3 Fault Sense+ 6 3 Fault Sense+ 6 4 CT 4 CT Gnd 5 DIP Package (N) Gate 8 Gnd 5 SOIC Package (M) Block Diagram 6V Internal Regulator I1 Fault CT CINT 2I1 Normal Fault Q1 Sense + VDD Sense – 50mV ON OFF ↑ ONESHOT ↓ Input 10I2 I2 6V Gate 5 Transistor Count: 82 Pin Description Pin Number Pin Name 1 VDD Supply: +11V to +50V. 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 Fault Overcurrent Fault Indicator: When the sense voltage exceeds threshold, open collector output is open circuit for 5µs (tG(ON)), then pulled low for tG(OFF). tG(OFF) is adjustable from CT. 4 CT Retry Timing Capacitor: Controls the off time (tG(OFF)) of the overcurrent retry cycle. (Duty cycle adjustment.) • 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. 5 Gnd 6 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. 7 Sense – Current Sense Comparator (–) Input: Connect to the low side of the sense resistor (usually power ground). 8 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. October 1998 Pin Function Circuit Ground 5-163 MIC5020 Micrel Absolute Maximum Ratings Operating Ratings Supply Voltage (VDD) .................................................. +55V Input Voltage ................................................ –0.5V to +15V Sense Differential Voltage .......................................... ±6.5V Sense + or Sense – to Gnd .......................... –0.5V to +50V Fault Voltage ............................................................... +50V Current into Fault ....................................................... 50mA Timer Voltage (CT) ..................................................... +5.5V Supply Voltage (VDD) .................................... +11V to +50V Temperature Range SOIC ...................................................... –40°C to +85°C Plastic DIP .............................................. –40°C to +85°C Electrical Characteristics TA = 25°C, Gnd = 0V, VDD = 12V, Sense +,– = 0V, Fault = Open, CT = Open, Gate CL = 1500pF unless otherwise specificed Symbol Parameter Condition D.C. Supply Current Min Typ Max Units 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 1.4 2.0 V Input Threshold 0.8 Input Hysteresis 0.1 V 20 40 µA 0.15 0.4 V –1 0.01 +1 µA Note 2 30 50 70 mV VDD = 12V 10 11 VDD = 50V 14 15 18 V Input Pull-Down Current Input = 5V 10 Fault Output Saturation Voltage Fault Current = 1.6mA Note 1 Fault Output Leakage Fault = 50V Current Limit Threshold Gate On Voltage V tG(ON) Gate On Time, Fixed Sense Differential > 70mV 2 5 10 µs tG(OFF) Gate Off Time, Adjustable Sense Differential > 70mV, CT = 0pF 10 20 50 µs tDLH Gate Turn-On Delay Note 3 400 800 ns tR Gate Rise Time Note 4 700 1500 ns tDLH Gate Turn-Off Delay Note 5 900 1500 ns tF Gate Fall Time Note 6 500 1500 ns fmax Maximum Operating Frequency Note 7 100 150 kHz Note 1 Voltage remains low for time affected by CT. Note 2 When using sense MOSFETs, it is recommended that RSENSE < 50Ω. Higher values may affect the sense MOSFET’s current transfer ratio. 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. 5-164 October 1998 MIC5020 Micrel Typical Characteristics Supply Current vs. Supply Voltage 3.5 Turn-On Time vs. Supply Voltage 900 VIN = 5V 1.5 VIN = 0V 1.0 1100 tOFF (ns) 2.5 2.0 1200 VGATE = 4V CL = 1500pF VIN = 0 to 5V Sq. Wave 800 tON (nS) ISUPPLY (mA) 3.0 Turn-Off Time vs. Supply Voltage 1000 700 600 VGATE = 4V CL = 1500pF VIN = 0 to 5V Sq. Wave 900 800 500 INCLUDES PROPAGATION DELAY INCLUDES PROPAGATION DELAY 400 5 10 15 20 25 30 35 40 45 50 VSUPPLY (V) Input Current vs. Input Voltage 100 700 5 10 15 20 25 30 35 40 45 50 VSUPPLY (V) 1200 25.0 VGATE = 4V 1000 60 800 tON (ns) IIN (µA) VSUPPLY = 12V 80 40 600 400 20 INCLUDES PROPAGATION DELAY 0 0 5 10 15 VIN (V) 20 200 1x102 25 5 Turn-On Time vs. Gate Capacitance Shutdown Duty Cycle (%) 0.5 1x103 1x104 CGATE (pF) 10 25 30 Overcurrent Shutdown Retry Duty Cycle tON = 5µs VSUPPLY = 12V 20.0 15.0 10.0 5.0 0.0 0.1 1x105 15 20 VSUPPLY (V) 1 10 100 CT (pF) 1000 10000 Sense Threshold vs. Temperature 80 Input VOLTAGE (mV) 70 60 Gate 50 Sense +, – Differential 40 TTL (H) 0V 15V (max.) 0V 50mV 0V Off Fault 30 Timing Diagram 1. Normal Operation 20 -60 -30 0 30 60 90 120 150 TEMPERATURE (°C) 5µs Input Gate Sense +, – Differential 20µs 5µs TTL (H) Input 0V 15V (max.) 0V Gate 50mV Sense +, – Differential 0V Off Fault TTL (H) 0V 15V (max.) 0V 50mV 0V Off Fault On Timing Diagram 2. Fault Condition, CT = Open October 1998 On On Timing Diagram 3. Fault Condition, CT = Grounded 5-165 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 CINT upon power up. An optional 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 CINT in a short time. When CINT is discharged, the INPUT is disabled, which turns off the GATE output; the FAULT output is enabled; 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 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 A 50mV comparator is provided for current sensing. The low level trip point minimizes I2R losses when power resistors are used for current sensing. Flexibility in choosing drain or 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 MIC5020 Micrel Lamp Driver Application Incandescent lamps have a high inrush current (low resistance) when turned on. The MIC5020 can perform a “soft start” by pulsing the MOSFET (overcurrent condition) until the filament is warm enough for its current to decrease (resistance increases). The sense resistor is selected so the voltage across the sense resistor drops below the sense threshold (50mV) as the filament becomes warm. The MOSFET is no longer pulsed to limit current and the lamp turns completely on. 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 (ISOURCE/ ISENSE) is provided by the MOSFET manufacturer. V+ (+13.2V, > 4.4A) V+ Load (+11V to +12V) Incandescent Lamp (#1157) 10µF 1 2 TTL Input (0V/5V) 3 4 MIC5020 VDD Gate Input Sense− Fault Sense+ CT Gnd +11V to +50V (+13.2V) 10µF N-Channel Power MOSFET (IRF540) 8 7 TTL Input (0V/5V) 6 5 V+ Solenoid +11V to +50V TTL Input 2 3 4 MIC5020 VDD Gate Input Sense− Fault Sense+ CT Gnd 8 7 Diode N-Channel Power MOSFET 6 5 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 3 MIC5020 VDD Gate Input Sense− Fault Sense+ CT Gnd 8 7 N-Channel Current Sensing Power MOSFET (IRCZ24) 6 5 RSENSE (10Ω) “( )” values apply to demo circuit. See text. 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. 1 2 4 RSENSE (0.041Ω) “( )” values apply to demo circuit. See text. 10µF 1 (3Ω, > 60W) 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: RSENSE = (r VTRIP RDS(ON)) / (ILOAD RDS(ON) – VTRIP) where: RSENSE = external “sense” resistor VTRIP = 50mV (0.050V) for the MIC5020 r = manufacturer’s current sense ratio: (ISOURCE/ISENSE) RDS(ON) = manufacturer’s power source on resistance ILOAD = load current (power source current) 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 (VDS(ON) very small) than to a short circuit (where VDS(ON) is approximately equal to the supply voltage). Adjustment of the sense resistor value by experiment starting from the above formula will provide the quickest selection of RSENSE. 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 RDS(ON) of 0.10Ω. A large 3Ω wirewound load resistor will cause inductive spikes which should be suppressed using a diode (using the same configuration as figure 2). 5-167 5 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. Load +40V max. 2N3904 +11V to +50V 10µF 1 2 150kHz max. 3 VDD Gate Input Sense− Fault Sense+ CT Gnd N-Channel Power MOSFET (IRF540) 8 7 6 2N3906 V+ 5 Load 4 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. MIC5020 +11V to +50V 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. The switched circuit voltage can be increased above 40V by selecting transistors with higher ratings. 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. 1 10µF 2 3 4 VDD Gate Input Sense Fault Sense CT Gnd 8 7 6 2.2M 5 RSENSE 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+ +11V to +50V 10µF TTL input Retry (H) Maintained (L) 1 2 3 10k to 100k 4 MIC5020 VDD Gate Input Sense− Fault Sense+ CT Q1 2N3904 Gnd 8 7 Load Load V+ +11V to +50V N-Channel Power MOSFET 10µF MIC5020 1 2 3 6 4 5 RSENSE VDD Gate Input Sense Fault Sense CT Gnd 8 7 6 5 2.2M RSENSE 74HC04 (example) 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. Figure 6b. Gate-to-Ground Pull Down The gate-to-ground configuration (refer to Figure 6b) is appropriate for resistive, inductive, or capacitive loads. This configuration will decrease the gate output voltage slightly more than the circuit shown in Figure 6a. 5-168 October 1998