LT1910 Protected High Side MOSFET Driver FEATURES DESCRIPTION n The LT(R)1910 is a high side gate driver that allows the use of low cost N-channel power MOSFETs for high side switching applications. It contains a completely self-contained charge pump to fully enhance an N-channel MOSFET switch with no external components. n n n n n n n n n 8V to 48V Power Supply Range Protected from -15V to 60V Supply Transients Short-Circuit Protected Automatic Restart Timer Open-Collector Fault Flag Fully Enhances N-Channel MOSFET Switches Programmable Current Limit, Delay Time and Autorestart Period Voltage Limited Gate Drive Defaults to Off State with Open Input Available in SO-8 Package APPLICATIONS n n n n n When the internal drain comparator senses that the switch current has exceeded the preset level, the switch is turned off and a fault flag is asserted. The switch remains off for a period of time set by an external timing capacitor and then automatically attempts to restart. If the fault still exists, this cycle repeats until the fault is removed, thus protecting the MOSFET. The fault flag becomes inactive once the switch restarts successfully. The LT1910 has been specifically designed for harsh operating environments such as industrial, avionics and automotive applications where poor supply regulation and/ or transients may be present. The device will not sustain damage from supply transients of -15V to 60V. Industrial Control Avionics Systems Automotive Switches Stepper Motor and DC Motor Control Electronic Circuit Breaker The LT1910 is available in the SO-8 package. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Fault Protected High Side Switch 5V 24V OFF ON 0.50 0.45 LT1910 V+ FAULT IN SENSE TIMER 0.1F IRFZ34 GATE GND 0.40 0.01 + 10F 50V LOAD TOTAL DROP (V) 5.1k FAULT OUTPUT Switch Drop vs Load Current 0.35 0.30 0.25 0.20 0.15 0.10 1910 TA01 0.05 0 0 1 3 2 LOAD CURRENT (A) 4 5 1910 TA02 1910fa 1 LT1910 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) Supply Voltage (Pin 8) ............................... -15V to 60V Input Voltage (Pin 4) ..................... (GND - 0.3V) to 15V GATE Voltage (Pin 5)................................................ 75V SENSE Voltage (Pin 6) ........................................ V+ 5V FAULT Voltage (Pin 3) .............................................. 36V Current (Pins 1, 2, 4, 5, 6, 8) ................................ 40mA Operating Temperature Range (Note 2) LT1910E ............................................... -40C to 85C LT1910I .............................................. -40C to 125C Junction Temperature Range ................ -40C to 125C Storage Temperature Range................... -65C to 150C Lead Temperature (Soldering, 10 sec) .................. 300C TOP VIEW GND 1 8 V+ TIMER 2 7 NC FAULT 3 6 SENSE IN 4 5 GATE S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125C, JA = 150C/W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1910ES8#PBF LT1910ES8#TRPBF 1910E 8-Lead Plastic SO -40C to 85C LT1910IS8#PBF LT1910IS8#TRPBF 1910I 8-Lead Plastic SO -40C to 125C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1910ES8 LT1910ES8#TR 1910E 8-Lead Plastic SO -40C to 85C LT1910IS8 LT1910IS8#TR 1910I 8-Lead Plastic SO -40C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. V+ = 12V to 48V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX IS Supply Current (Off State) V+ = 48V, VIN = 0.8V UNITS 1.2 1.9 2.5 mA 0.8 1.2 mA IS(ON) Delta Supply Current (On State) VIN = 2V, Measure Increase in IS VINH Input High Voltage E-Grade I-Grade l l VINL Input Low Voltage E-Grade I-Grade l l IIN Input Current VIN = 2V VIN = 5V l l 15 55 30 110 CIN Input Capacitance (Note 3) VT(TH) Timer Threshold Voltage VIN = 2V, Adjust VT l 2.6 2.9 3.2 3.2 3.5 3.8 V 9 14 20 A 50 65 0.33 80 mV %/C 2 3.5 V V 0.8 0.7 V V 50 185 A A 5 VT(CL) Timer Clamp Voltage VIN = 0.8V IT Timer Charge Current VIN = VT = 2V VSENSE Drain-Sense Threshold Voltage Temperature Coefficient (Note 3) pF V 1910fa 2 LT1910 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. V+ = 12V to 48V unless otherwise noted. SYMBOL PARAMETER CONDITIONS ISENSE Drain Sense Input Current V+ = 48V, VSENSE = 65mV Gate Voltage Above Supply V+ = 8V V+ = 12V l V+ = 24V E-Grade I-Grade V+ = 48V E-Grade I-Grade VGATE - V+ MIN VF(TH) FAULT Output High Threshold Voltage FAULT Output Low Threshold Voltage VIN = 2V, IF = 1mA, Adjust VT VFOL FAULT Output Low Voltage IF = 1mA tON Turn-On Time tOFF Turn-Off Time tOFF(CL) Current Limit Turn-Off Time V+ = 24V, VGATE = 32V, CGATE = 1nF V+ = 24V, VGATE = 2V, CGATE = 1nF V+ = 24V, (V+ - VSENSE)0.1V, CGATE = 1nF TYP MAX 0.5 1.5 A 4 7 4.5 8.5 6 10 V V l l 10 10 12 12 14 15 V V l l 10 10 12 12 14 15 V V 3.1 3.0 3.4 3.3 3.7 3.6 V V 0.07 0.4 V 220 400 s 25 100 s 20 50 s l Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT1910E is guaranteed to meet performance specifications from 0C to 70C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation 100 UNITS with statistical process controls. The LT1910I is guaranteed to meet performance specifications over the full -40C to 125C operating temperature range. Note 3: Guaranteed but not tested. TYPICAL PERFORMANCE CHARACTERISTICS Input Voltage vs Temperature Supply Current vs Supply Voltage 3.6 Supply Current vs Temperature 5.0 TA = 25C 3.4 1.8 ON STATE 2.8 2.6 2.4 2.2 OFF STATE 2.0 1.8 INPUT VOLTAGE (V) 4.0 SUPPLY CURRENT (mA) SUPPLY CURRENT (mA) 3.2 3.0 3.5 3.0 ON STATE 2.5 OFF STATE 2.0 1.5 1.0 1.6 1.6 VINH 1.4 VINL 1.2 1.0 0.5 1.4 1.2 2.0 V+ = 48V 4.5 0 10 30 40 20 SUPPLY VOLTAGE (V) 50 1910 G01 0 -50 -25 25 50 75 0 TEMPERATURE (C) 100 125 1910 G02 0.8 -50 -25 75 0 25 50 TEMPERATURE (C) 100 125 1910 G03 1910fa 3 LT1910 TYPICAL PERFORMANCE CHARACTERISTICS Timer Threshold Voltage vs Temperature Input Current vs Temperature 3.2 TIMER THRESHOLD VOLTAGE (V) 180 INPUT CURRENT (A) 160 140 VIN = 5V 120 100 80 60 40 VIN = 2V 3.8 VIN = 2V 3.1 TIMER CLAMP VOLTAGE (V) 200 Timer Clamp Voltage vs Temperature 3.0 2.9 2.8 2.7 VIN 0.8V 3.7 3.6 3.5 3.4 3.3 20 25 50 75 0 TEMPERATURE (C) 100 2.6 -50 125 -25 75 0 25 50 TEMPERATURE (C) 1910 G04 Drain Sense Threshold Voltage vs Temperature 90 DRAIN SENSE THRESHOLD VOLTAGE (mV) VIN = VT = 2V TIMER CHARGE CURRENT (A) 18 16 14 12 10 8 -50 75 0 25 50 TEMPERATURE (C) -25 100 V+ = 24V 85 80 75 70 65 60 55 50 45 40 -50 125 -25 25 50 75 0 TEMPERATURE (C) 1910 G07 FAULT THRESHOLD VOLTAGE (V) MOSFET GATE DRIVE CURRENT (A) 3.7 TA = 25C V+ = 8V 1 V+ = 12V V+ 24V 0.1 0 2 4 6 8 10 VGATE - V+ (V) 12 14 16 1910 G10 0 25 50 75 TEMPERATURE (C) 100 100 125 3.6 MOSFET Gate Voltage Above V+ (VGATE - V+) vs Supply Voltage 16 14 TA = 25C TA = 125C 12 TA = -40C 10 8 6 4 2 0 5 0 10 15 20 25 30 35 40 45 50 SUPPLY VOLTAGE (V) LTC1266 * F04 Fault Output Low Voltage vs Temperature 0.20 VIN = 2V IF = 1mA 3.5 FAULT HIGH THRESHOLD 3.4 3.3 3.2 FAULT LOW THRESHOLD 3.1 3.0 -50 125 1910 G06 Fault Threshold Voltage vs Temperature 10 -25 1910 G08 MOSFET Gate Drive Current vs VGATE - V+ 100 3.2 -50 125 1910 G05 Timer Charge Current vs Tempeature 20 100 MOSFET GATE VOLTAGE ABOVE V+ (VGATE - V+) (V) -25 FAULT OUTPUT LOW VOLTAGE (V) 0 -50 IF = 1mA 0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 -25 0 25 50 75 TEMPERATURE (C) 100 125 1910 G11 0 -50 -25 25 50 75 0 TEMPERATURE (oC) 100 125 1910 G012 1910fa 4 LT1910 TYPICAL PERFORMANCE CHARACTERISTICS Turn-On Time vs Temperature 400 100 300 250 200 AUTOMATIC RESTART PERIOD (ms) TURN-OFF TIME (Ms) TURN-ON TIME (Ms) 1000 V+ = 24V 90 VGATE = 2V CGATE = 1nF 80 V+ = 24V VGATE = 32V 350 CGATE = 1nF 70 60 50 40 30 NORMAL 20 150 CURRENT LIMIT 10 100 -50 Automatic Restart Period vs Temperature Turn-Off Time vs Temperature -25 75 0 25 50 TEMPERATURE (oC) 100 125 0 -50 -25 25 50 75 0 TEMPERATURE (oC) 1910 G13 100 125 1910 G014 V+ = 24V CT = 3.3F CT = 1F 100 CT = 0.33F CT = 0.1F 10 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C) 1910 G15 PIN FUNCTIONS GND (Pin 1): Common Ground. TIMER (Pin 2): A timing capacitor, CT , from the TIMER pin to ground sets the restart time following overcurrent detection. Upon detection of an overcurrent condition, CT is rapidly discharged to less than 1V and then recharged by a 14A nominal current source back to the 2.9V timer threshold, whereupon the restart is attempted. Whenever TIMER pulls below 2.9V, the GATE pin pulls low to turn off the external switch. This cycle repeats until the overcurrent condition goes away and the switch restarts successfully. During normal operation the pin clamps at 3.5V nominal. FAULT (Pin 3): The FAULT pin monitors the TIMER pin voltage and indicates the overcurrent condition. Whenever the TIMER pin is pulled below 3.3V at the onset of a current limit condition, the FAULT pin pulls active LOW. The FAULT pin resets HIGH immediately when the TIMER pin ramps above 3.4V during autorestart. The FAULT pin is an open-collector output, thus requiring an external pull-up resistor and is intended for logic interface. The resistor should be selected with a typical 1mA pull-up at low status and less than 2mA under worst-case conditions. IN (Pin 4): The IN pin threshold is TTL/CMOS compatible and has approximately 200mV of hysteresis. When the IN pin is pulled active HIGH above 2V, an internal charge pump is activated to pull up the GATE pin. The IN pin can be pulled as high as 15V regardless of whether the supply is on or off. If the IN pin is left open, an internal 75k pull-down resistor pulls the pin below 0.8V to ensure that the GATE pin is inactive LOW. GATE (Pin 5): The GATE pin drives the power MOSFET gate. When the IN pin is greater than 2V, the GATE pin is pumped approximately 12V above the supply. It has relatively high impedance (the equivalence of a few hundred k) when pumped above the rail. Care should be taken to minimize any loading by parasitic resistance to ground or supply. The GATE pin pulls LOW when the TIMER pin falls below 2.9V. SENSE (Pin 6): The SENSE pin connects to the input of a supply-referenced comparator with a 65mV nominal offset. When the SENSE pin is taken more than 65mV below supply, the MOSFET gate is driven LOW and the timing capacitor is discharged. The SENSE pin threshold has a 0.33%/C temperature coefficient (TC), which closely matches the TC of the drain-sense resistor formed from the copper trace of the PCB. For loads requiring high inrush current, an RC timing delay can be added between the drain-sense resistor and the SENSE pin to ensure that the current-sense comparator does not false trigger during start-up (see Applications 1910fa 5 LT1910 PIN FUNCTIONS Information). A maximum of 10k can be inserted between a drain-sense resistor and the SENSE pin. If current sensing is not required, the SENSE pin is tied to supply. V+ (Pin 8): In addition to providing the operating current for the LT1910, the V+ pin also serves as the Kelvin connection for the current-sense comparator. The V+ pin must be connected to the positive side of the drain-sense resistor for proper current-sensing operation. BLOCK DIAGRAM V+ 14A - 3.3V FAULT + V+ TIMER 2.9V + - + 65mV + - - SENSE + 1.4V 75k IN + - GATE 1.4V OSCILLATOR AND CHARGE PUMP - 75k 250 1910 BD OPERATION (Refer to the Block Diagram) The LT1910 GATE pin has two states, off and on. In the off state it is held LOW, while in the on state it is pumped to 12V above the supply by a self-contained 750kHz charge pump. The off state is activated when either the IN pin is below 0.8V or the TIMER pin is below 2.9V. Conversely, for the on state to be activated, the IN pin must be above 2V and the TIMER pin must be above 2.9V. The IN pin has approximately 200mV of hysteresis. If it is left open, the IN pin is held LOW by a 75k resistor. Under normal conditions, the TIMER pin is held a diode drop above 2.9V by a 14A pull-up current source. Thus the TIMER pin automatically reverts the GATE pin to the on state if the IN pin is above 2V. The SENSE pin normally connects to the drain of the power MOSFET, which returns through a low value drain-sense resistor to supply. In order for the sense comparator to accurately sense the MOSFET drain current, the V+ pin must be connected directly to the positive side of the drain-sense resistor. When the GATE pin is on and the MOSFET drain current exceeds the level required to generate a 65mV drop across the drain-sense resistor, the sense comparator activates a pull-down NPN which rapidly pulls the TIMER pin below 2.9V. This in turn causes the timer comparator to override the IN pin and set the GATE pin to the off state, thus protecting the power MOSFET. When the TIMER pin is pulled below 3.3V, the fault comparator 1910fa 6 LT1910 OPERATION also activates the open-collector NPN to pull the FAULT pin LOW, indicating an overcurrent condition. When the MOSFET gate voltage is discharged to less than 1.4V, the TIMER pin is released. The 14A current source then slowly charges the timing capacitor back to 2.9V where the charge pump again starts to drive the GATE pin HIGH. If a fault condition still exists, the sense comparator threshold will again be exceeded and the timer cycle will repeat until the fault is removed. The FAULT pin becomes inactive HIGH if the TIMER pin charges up successfully above 3.4V (see Figure 1). OFF NORMAL OVERCURRENT NORMAL IN 0V V+ 12V GATE TIMER 0V 3.5V 2.9V 3.4V 0V 5V FAULT 0V 1910 F01 Figure 1. Timing Diagram APPLICATIONS INFORMATION Input/Supply Sequencing There are no input/supply sequencing requirements for the LT1910. The IN pin may be taken up to 15V with the supply at 0V. When the supply is turned on with the IN pin set HIGH, the MOSFET turn-on will be inhibited until the timing capacitor charges up to 2.9V (i.e., for one restart cycle). Isolating the Inputs Operation in harsh environments may require isolation to prevent ground transients from damaging control logic. The LT1910 easily interfaces to low cost optoisolators. The network shown in Figure 2 ensures that the input will be pulled above 2V, but not exceed the absolute maximum rating for supply voltages of 12V to 48V over the entire 2k The LT1910 uses supply referenced current sensing. One input of the current-sense comparator is connected to a drain-sense pin, while the second input is offset 65mV below the supply inside the device. For this reason, Pin 8 of the LT1910 must be treated not only as a supply pin, but also as the reference input for the current-sense comparator. Figure 3 shows the proper drain-sense configuration for the LT1910. Note that the SENSE pin goes to the drain end of the sense resistor, while the V+ pin is connected 5V 100k FAULT OUTPUT LT1910 4 LOGIC GROUND Drain-Sense Configuration 24V 12V TO 48V LOGIC INPUT temperature range. The optoisolator must have less than 20A of dark current (leakage) at hot in order to maintain the off state (see Figure 2). INPUT IN R1 5.1k 3 RS 0.02 (PTC) LT1910 8 V+ FAULT 6 4 IN SENSE 5 2 TIMER GATE Q1 IRFZ34 GND 51k GND 1 1 1910 F02 CT 1F + C1 100F 50V 24V 2A SOLENOID POWER GROUND 0V Figure 2. Isolating the Input 1910 F03 Figure 3. Drain-Sense Configuration 1910fa 7 LT1910 APPLICATIONS INFORMATION to the supply at the same point as the positive end of the sense resistor. The drain-sense threshold voltage has a positive temperature coefficient, allowing PTC sense resistors to be used (see Printed Circuit Board Shunts). The selection of RS should be based on the minimum threshold voltage: RS = 50mV/ISET Thus the 0.02 drain-sense resistor in Figure 3 will yield a minimum trip current of 2.5A. This simple configuration is appropriate for resistive or inductive loads that do not generate large current transients at turn-on. Automatic Restart Period The timing capacitor, CT , shown in Figure 3 determines the length of time the power MOSFET is held off following a current limit trip. Curves are given in the Typical Performance Characteristics to show the restart period for various values of CT . For example, CT = 0.33F yields a 50ms restart period. Defeating Automatic Restart Some applications are required to remain off after a fault occurs. When the LT1910 is being driven from CMOS logic, this can be easily implemented by connecting resistor R2 between the IN and TIMER pins as shown in Figure 4. R2 supplies the sustaining current for an internal SCR which latches the TIMER pin LOW under a fault condition. The FAULT pin is set active LOW when the TIMER pin falls below 3.3V. This keeps the MOSFET gate from turning on and the FAULT pin from resetting HIGH until the IN pin has been recycled. CT is used to prevent the FAULT pin from glitching whenever the IN pin recycles to turn on the MOSFET unsuccessfully under an existing fault condition. Inductive vs Capacitive Loads Turning on an inductive load produces a relatively benign ramp in MOSFET current. However, when an inductive load is turned off, the current stored in the inductor needs somewhere to decay. A clamp diode connected directly across each inductive load normally serves this purpose. If a diode is not employed, the LT1910 clamps the MOSFET gate 0.7V below ground. This causes the MOSFET to resume conduction during the current decay with (V+ + VGS + 0.7V) across it, resulting in high dissipation peaks. Capacitive loads exhibit the opposite behavior. Any load that includes a decoupling capacitor will generate a current equal to CLOAD * (V/t) during capacitor in-rush. With large electrolytic capacitors, the resulting current spike can play havoc with the power supply and false trip the current-sense comparator. Turn-on V/t is controlled by the addition of the simple network shown in Figure 5. This network takes advantage of the fact that the MOSFET acts as a source follower during turn-on. Thus the V/t on the source can be controlled by controlling the V/t on the gate. CURRENT LIMIT DELAY NETWORK V+ SENSE 5V FAULT OUTPUT 5V ON = 5V CMOS LOGIC OFF = 0V R2 2k 4 2 RS 0.01 6 LT1910 V/t CONTROL NETWORK 1N4148 FAULT IN LT1910 TIMER GND CT 1F 1N4148 CD RD (10k) R1 5.1k 3 8 24V GATE GND 1 1 C2 50F 50V 5 + R1 100k R2 100k C1 + Q1 IRFZ34 15V 1N4744 1910 F05 1910 F04 Figure 4. Latch-Off Configuration (Autorestart Defeated) CLOAD Figure 5. Control and Current Limit Delay 1910fa 8 LT1910 APPLICATIONS INFORMATION The turn-on current spike into CLOAD is estimated by: IPEAK = CLOAD * VG - VTH R1* C1 RD and CD delay the overcurrent trip for drain currents up to approximately 10 * ISET, above which the diode conducts and provides immediate turn-off (see Figure 7). To ensure proper operation of the timer, CD must be CT . where VTH is the MOSFET gate threshold voltage. VG is obtained by plotting the equation: VGATE R1 on the graph of Gate Drive Current (IGATE) vs Gate Voltage (VGATE) as shown in Figure 6. The value of VGATE at the intersection of the curves for a given supply is VG. For example, if V+ = 24V and R1 = 100k, then VG = 18.3V. For VTH = 2V, C1 = 0.1F and CLOAD = 1000F, the estimated IPEAK = 1.6A. The diode and the second resistor in the network ensure fast current limit turn-off. When turning off a capacitive load, the source of the MOSFET can "hang up" if the load resistance does not discharge CLOAD as fast as the gate is being pulled down. If this is the case, a 15V zener may be added from gate to source to prevent VGS(MAX) from being exceeded. 800 GATE DRIVE CURRENT (A) 700 600 V+ = 48V V+ = 24V TRIP DELAY TIME (1 = RDCD) IGATE = 10 1 0.1 0.01 1 10 100 MOSFET DRAIN CURRENT (1 = SET CURRENT) 1910 F07 Figure 7. Current Limit Delay Time Printed Circuit Board Shunts The sheet resistance of 1oz copper clad is approximately 5 * 10-4/square with a temperature coefficient of 0.39%/C. Since the LT1910 drain-sense threshold has a similar temperature coefficient (0.33%/C), this offers the possibility of nearly zero TC current sensing using the "free" drain-sense resistor made out of PC trace material. 500 V+ = 12V 400 V+ = 8V IGATE = VGATE/105 300 200 100 0 A conservative approach is to use 0.02" of width for each 1A of current for 1oz copper. Combining the LT1910 drain sense threshold with the 1oz copper resistance results in a simple expression for width and length: Width (1oz Cu) = 0.02" * ISET 0 10 20 40 30 GATE VOLTAGE (V) 50 60 1910 F06 Figure 6. Gate Drive Current vs Gate Voltage Adding Current Limit Delay When capacitive loads are being switched or in very noisy environments, it is desirable to add delay in the drain current-sense path to prevent false tripping (inductive loads normally do not need delay). This is accomplished by the current limit delay network shown in Figure 5. Length (1oz Cu) = 2" The width for 2oz copper would be halved while the length would remain the same. Bends may be incorporated into the resistor to reduce space; each bend is equivalent to approximately 0.6 * the width of a straight length. Kelvin connection should be employed by running a separate trace from the ends of the resistor back to the LT1910's V+ and SENSE pins. See Application Note 53 for further information on printed circuit board shunts. 1910fa 9 LT1910 APPLICATIONS INFORMATION between the V+ and GND pins is highly recommended. An RC snubber with a transient suppressor are an absolute necessity. Note however that resistance should not be added in series with the V+ pin because it will cause an error in the current-sense threshold. Low Voltage/Wide Supply Range Operation When the supply is less than 12V, the LT1910's charge pump does not produce sufficient gate voltage to fully enhance the standard N-channel MOSFET. For these applications, a logic-level MOSFET can be used to extend the operating supply down to 8V. If the MOSFET has a maximum VGS rating of 15V or greater, then the LT1910 can also operate up to a supply voltage of 60V (absolute maximum rating of the V+ pin). Low Side Driving Although the LT1910 is primarily targeted at high side (grounded load) switch applications, it can also be used for low side (supply connected load) switch applications. Figures 8a and 8b illustrate the LT1910 driving low side power MOSFETs. Because the LT1910 charge pump tries to pump the gate of the N-channel MOSFET above the supply, a clamp Zener is required to prevent the VGS (absolute maximum) of the MOSFET from being exceeded. Protecting Against Supply Transients The LT1910 is 100% tested and guaranteed to be safe from damage with 60V applied between the V+ and GND pins. However, when this voltage is exceeded, even for a few microseconds, the result can be catastrophic. For this reason it is imperative that the LT1910 is not exposed to supply transients above 60V. A transient suppressor, such as Diodes Inc.'s SMAJ48A, should be added between the V+ and GND pins for such applications. 12V TO 48V 5V FAULT OUTPUT 2 IN SENSE TIMER GATE GND 1 CT 1F 0V RS 0.01 (PTC) 8 6 + C1 100F 100V 4A LOAD 5 Q1 IRFZ44 15V 1N4744 1910 F08a Figure 8a. Low Side Driver with Load Current Sensing 8V TO 24V 5V V+ FAULT LT1910 When the operating voltage approaches the 60V absolute maximum rating of the LT1910, local supply decoupling INPUT 4 INPUT For proper current sense operation, the V+ pin is required to be connected to the positive side of the drain-sense resistor (see Drain-Sense Configuration). Therefore, the supply should be adequately decoupled at the node where the V+ pin and drain sense resistor meet. Several hundred microfarads may be required when operating with a high current switch. FAULT OUTPUT R1 5.1k 3 R1 5.1k 3 LT1910 8 V+ FAULT 6 4 IN SENSE 5 2 TIMER GATE HV HV LOAD 51 Q1 IRF630 15V 1N4744 GND 1 + 2N2222 CT 1F RS 0.02 LT1006 C1 + - 10F 50V 51 1910 F08b Figure 8b. Low Side Driver for Source Current Sensing 1910fa 10 LT1910 APPLICATIONS INFORMATION The LT1910 gate drive is current limited for this purpose so that no resistance is needed between the GATE pin and Zener. Current sensing for protecting low side drivers can be done in several ways. In the Figure 8a circuit, the supply voltage for the load is assumed to be within the supply operating range of the LT1910. This allows the load to be returned to supply through current-sense resistor, RS, providing normal operation of the LT1910 protection circuitry. the current sense must be moved to the source of the low side MOSFET. Figure 8b shows an approach to source sensing. An operational amplifier (must common mode to ground) is used to level shift the voltage across RS up to the drainsense pin. This approach allows the use of a small sense resistor which could be made from PC trace material. The LT1910 restart timer functions the same as in the high side switch application. If the load cannot be returned to supply through RS, or the load supply voltage is higher than the LT1910 supply, PACKAGE DESCRIPTION S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 - .197 (4.801 - 5.004) NOTE 3 .045 p.005 .050 BSC 8 .245 MIN 7 6 5 .160 p.005 .150 - .157 (3.810 - 3.988) NOTE 3 .228 - .244 (5.791 - 6.197) .030 p.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 - .020 s 45o (0.254 - 0.508) .008 - .010 (0.203 - 0.254) 3 4 .053 - .069 (1.346 - 1.752) .004 - .010 (0.101 - 0.254) 0o- 8o TYP .016 - .050 (0.406 - 1.270) NOTE: 1. DIMENSIONS IN 2 .014 - .019 (0.355 - 0.483) TYP INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm) .050 (1.270) BSC SO8 0303 1910fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 11 LT1910 TYPICAL APPLICATION Protected 1A Automotive Solenoid Driver with Overvoltage Shutdown 8V TO 24V OPERATING 32V TO 60V SHUTDOWN 5V FAULT OUTPUT R1 5.1k 3 INPUT 30V 1N6011B Q1 MTD3055EL GND 1N4148 R2 10k RS 0.03 (PTC) LT1910 8 V+ FAULT 6 4 IN SENSE 5 2 TIMER GATE 1 2N3904 R3 5.1k CT 1F POWER GROUND + C1 10F 100V 24V 1A SOLENOID 1910 TA03 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC 1153 Autoreset Electronic Circuit Breaker Programmable Trip Current, Fault Status Output LTC1155 Dual High Side Micropower MOSFET Driver Operates from 4.5V to 18V, 85A On Current, Short-Circuit Protection LT1161 Quad Protected High Side MOSFET Driver 8V to 48V Supply Range, Individual Short-Circuit Protection LTC1163 Triple 1.8V to 6V High Side MOSFET Driver 0.01A Standby Current, Triple Driver in SO-8 Package LTC1255 Dual 24V High Side MOSFET Driver Operates from 9V to 24V, Short-Circuit Protection (R) LTC1477 Protected Monolithic High Side Switch Low RDS(ON) 0.07 Switch, 2A Short-Circuit Protected LTC1623 SMBus Dual High Side Switch Controller 2-Wire SMBus Serial Interface, Built-In Gate Charge Pumps LTC1693 Family High Speed Single/Dual N-Channel/P-Channel MOSFET Drivers 1.5A Peak Output Current, 4.5V VCC 13.2V, SO-8 Package LTC1710 SMBus Dual Monolithic High Side Switch Two Low RDS(ON) 0.4/300mA Switches in 8-Lead MSOP Package LTC4412 Low Loss PowerPathTM Controller Implements "Ideal Diode" Function, ThinSOTTM Package PowerPath and ThinSOT are trademarks of Linear Technology Corporation. 1910fa 12 Linear Technology Corporation LT 0409 REV A * PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com (c) LINEAR TECHNOLOGY CORPORATION 2009