The second generation of the HITFET family offers low RDS(on) and restart function in the SOT223 and D-Pak with low-input current

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1 HL Application Note BSP 76, BSP 77, BSP 78, BTS 118D, BTS 134D, BTS 142 D 1 The second generation of the HITFET family offers low RDS(on) and restart function in the SOT223 and D-Pak with low-input current drive Benno Köppl Introduction The age of Siemens Smart Power low-side switches began with the introduction of the TEMPFET (TEMperature Protected FET). By integrating further protection functions such as overvoltage and ESD protection and du/dt limiting and combining these with the familiar TEMPFET chip-on-chip technology, the HITFET family of switches with 18 mω through 100 mω and 60V V DS clamping voltage represents a logical further development in intelligent single-channel low-side switches. A distinguishing feature of the second generation of the HITFET family is the new S- smart technology that has enabled a 35% reduction in chip surface area while retaining the R DS(on). The HITFET range offered until now is being extended in the 28 mω mω range with 42V V DS clamping voltage. Switches in SOT223 and D-Pak formats are being offered as package variants. In view of the fact that the main area of application will be 12V onboard networks in automobiles, the drain source voltage range has been set to 42V. This has enabled low R DS(on) values to be achieved in small packages. During the development of the second generation, particular focus was laid on low input currents in all operating states to minimize the demands made on any µ-controller that may be used for drive purposes. As a result it has been possible to reduce the input currents from a previous maximum of 6 ma to a maximum of 300 µa on thermal shut down. The protection functions implemented as latch type in the first generation HITFET - thermal overload protection and short-circuit protection - have been implemented as an automatic restart type in the second generation. 1 The BSP75/A device is also a member of the HITFET 2 family and has mainly the same functionality. As it is based on a different technolgy, it shows different behavoir in details. A Appnote for BSP75 is available, too. APPHIT2.doc 1 HL LH TM 2-10/98

2 Drain Overvoltage prot. Gate drive Gate Power Input Drain transistor ESD Short circuit prot. Overtemp. prot. Current limit. Figure 1 Block diagram of the new HITFET family Source/ ground The advantages of the first generation, such as overvoltage and ESD protection, edge steepness limiting for the input voltage and current limitation, have been retained. The analog drive option and the logic level type have also been incorporated. Figure 1 shows a block diagram to illustrate the structure of the new HITFET family. Table 1 provides an overview of the new HITFET family. The entire HITFET family is illustrated in the Appendix. Type V DS(AZ) [V] R DS (ON) I D ISO (min) [A] I D (lim) min [A] Package [mω] BSP SOT 223 BSP SOT 223 BSP SOT 223 BTS D-Pak BTS D-Pak BTS D-Pak Table 1 Overview of the second generation single-channel HITFET family 1 Protection functions The protection functions of the new HITFET comprise protection against short circuits, overload, overtemperature and overvoltage. In addition, it has very good ESD characteristics. 1.1 Overload, short-circuit and overtemperature protection Overload protection, which includes both short-circuit and overtemperature protection, is implemented as a multi-stage function in the first generation HITFET. This means that if the internal current limiting value I D(lim) is exceeded, the Mosfet is not deactivated immedi- APPHIT2.doc 2 HL LH TM 2-10/98

3 ately. Instead, the current is limited to I D(lim). The component is operated in the analog range of the curve, leading to an increase in the drain source voltage. This operating state results in an increase in chip temperature. To prevent the maximum junction temperature from being exceeded, the Mosfet is switched off by means of a temperature sensor. This enables the component to protect itself. In principle, this behavior also applies to the second generation HITFET. However, a very high current limiting value has been selected in relation to the nominal current to avoid activation of the current limiting function when loads with a capacitive effect, such as filament lamps, are switched on. This makes it possible to switch on the load without delay. For example, a conventional 21W lamp for automotive applications can be switched with a BSP 78, without affecting its turn-on characteristics, in order to implement a rapid-reaction brake light. V GS I D (5A/div) V DS Figure 2 Switching on a 21W lamp with BSP78 at room temperature 1.2 Short-circuit protection If the Hitfet is switched on with an existing short circuit, the voltage increases above drain source. If this exceeds 2.5V, current limiting is activated. This operating mode results in a rapid temperature increase (dependent on cooling). If a chip temperature of 175 C (typ.) is reached, the component will deactivate itself. In contrast to the first generation HITFET, the new HITFET is not implemented as a "latch type" but has restart functionality on cooling. The temperature hysteresis is typically 10 K. Figure 3 illustrates this behavior when switching on with an existing short circuit. APPHIT2.doc 3 HL LH TM 2-10/98

4 Figure 3 also shows that the current limiting function is temperature-dependent. The current increases initially to I L(SCp). This value corresponds to the current limiting value at a junction temperature (T j ) slightly higher than room temperature. The high power dissipation in the chip causes a rapid increase in chip temperature and the current limiting value approaches the value for T j =175 C. If the chip reaches 175 C, it is deactivated. The chip then begins to cool down. It is reactivated with a typical hysteresis of 10 C. The current always sets itself to the current limiting value at a junction temperature of approximately 165 C (I L(SCr) ). The time between switch-off and restart is mainly dependent on the cooling of the device. V GS I D (10A/div) V DS Figure 3 Activation of a BSP78 to an existing short circuit; Temperature behavior of current limitation (dependent on cooling) If a short circuit occurs during operation, the current increases, starting at the value of the load current previously flowing, until activation of the current limiting circuit at V DS >2.5V. Figure 4 illustrates this behavior at a battery voltage of 14V. Due to the extremely high power dissipation and rapid temperature rise in the chip, this case shows clearly the dependency of the current limiting function on temperature. The second-generation HITFET is short-circuit proof across the entire operating voltage range. To ensure that overtemperature protection works properly in all operating ranges, the protection logic is supplied via the input voltage V IN. APPHIT2.doc 4 HL LH TM 2-10/98

5 The supply threshold for the protection logic is by design lower than the threshold voltage of the DMOS. This ensures that the protection function will work effectively before the Mosfet switches on. V GS I D V DS Figure 4 Short circuit during normal operation Note: Because the current limiting is not active at V DS < 2.5V, theoretically an operating mode is possible in which short-circuit currents exceed the specified values. In practice, however, at a supply voltage of less than 2.5V, the HITFET pure resistance limits the currents to a tolerable level. Overtemperature protection is also active in these cases and deactivates the device promptly, ensuring full short-circuit protection in this voltage range as well. 1.3 Switching inductive loads - overvoltage protection For operation of inductive loads such as coils, relays and motors, the HITFET provides active Zener clamping between drain and gate, in order to protect the component against overvoltages. If a voltage of typically 47 V is exceeded when inductive loads are switched off, the Zener diode chain starts to conduct and activates the gate. In this case the possible inductiv switch off energy is many times higher than for avalanche breakdown. Figure 5 shows the switching of a solenoid valve with a clearly visible switch point (change in inductance). The active Zener clamping with U DS(AZ) > 42 V makes it possible to achieve fast switch-off times with a high di/dt without risk to the component. APPHIT2.doc 5 HL LH TM 2-10/98

6 V GS I D V DS Figure 5 Switching a solenoid valve with a BSP78 Application example: Inductive overvoltages typically occur when a relay is switched off. If the HITFET is used as a relay driver, it is not necessary to use a freewheeling diode, as V DS is limited within the component. This overvoltage protection requires no supply voltage. V BB IN HITFET D S Figure 6 HITFET as a relay driver APPHIT2.doc 6 HL LH TM 2-10/98

7 1.4 ESD protection The HITFET family offers protection against electrostatic discharge (ESD) greater than 2 kv for every pin combination. This significantly reduces the risk to components during handling. APPHIT2.doc 7 HL LH TM 2-10/98

8 2 Differences between HITFET generations 1 and 2 The following table describes the differences between the two generations. HITFET 1st generation HITFET 2nd generation R DS(on) range mohm mohm Package TO 220-3/-5 SOT 223 D-Pak Structure Chip-on-chip Monolithic Maximum current consumption < 6.0 ma < 300 µa at input (protection mode) Maximum current consumption < 6.0 ma < 300 µa at input (normal opera- tion) Overtemperature protection Latch function Restart function with 10K hysteresis V DS 60 V 42 V Current limiting I D(lim) 1.4 to 3x I D(ISO) 2.3 to 5.3x I D(ISO) Current sense available (BTS 9xx) not available Adjustable current limitation available (BTS 9xx) not available Technology m-smart S-Smart 3 Areas of application for the 2 nd -generation HITFET Its comprehensive protection functions make the HITFET 2 suitable for many different areas of application and loads such as relays, signal lamps, motor bridges, valves, etc. The following characteristics above all qualify it for the rugged automotive world: Full functionality up to Tj = 150 C in normal operation and in overload conditions (operation with current limiting) No minimum supply voltage required for the protection functions to work Good ESD characteristics Small package formats combined with low R DS(on) The high current limiting capability makes the HITFET2 particularly suitable for delay-free switching of lamps (e.g. BSP78 for 21 W brake lights). Where the HITFET is used as a high-side switch, it is merely necessary to ensure that the input-source protection circuitry is protected against currents > 2mA if 10V V in is exceeded. The simplest protection in this case is to include a resistance in the supply to the input. APPHIT2.doc 8 HL LH TM 2-10/98

9 4 Appendix Overview of the HITFET family R on in mò 500 BSP 75 Low Side Load 200 BSP BTS 117 BTS 917 BSP 77 BTS BTS 133 BTS 933 BSP 78 BTS BTS 141 BTS 941 BTS BTS 149 BTS HITFET 1 TO220 TO220 SOT SOT HITFET 2 D-Pak D-Pak 3 pins pins 5 pins pins 3 pins pins Power Semiconductors Smart Power Switches HL PS PM 2 08/98 Remark: This information describes the type of component and shall not be considered as assured charcteristics. APPHIT2.doc 9 HL LH TM 2-10/98