Freescale Semiconductor Application Note Document Number: AN4858 Rev. 1.0, 2/2014 Inductive Switching for Dual 24 and 36 V High-side Switch Families 1 Introduction Contents This application note describes the behavior of the SMARTMOS Dual 24 – 36 V high-side switch devices (Table 1), at switch OFF when driving inductive loads. These intelligent high-side switches are designed to be used in 24 V systems such as trucks and busses (XS4200). They can be used in industrial (XSD200) and 12 V applications as well. The low RDS(on) channels can control incandescent lamps, LEDs, solenoids, or DC motors. Control, device configuration, and diagnostics are performed through a 16-bit SPI interface, allowing easy integration into existing applications. For a complete feature description, refer to the individual data sheets. Table 1. eXtreme Switch Core XS4200 Family XSD200 Family MC06XS4200 MC06XSD200 MC10XS4200 MC10XSD200 MC20XS4200 MC16XSD200 © Freescale Semiconductor, Inc., 2014. All rights reserved. 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 24 and 36 V eXtreme Switch Inductive Switching2 2.1 Clamped Inductive Switching (CIS) . . . . . . 2 2.2 Inductive Switching with External Clamp > -2.0 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.3 Inductive Switching with External Clamp < -2.0 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Revision History. . . . . . . . . . . . . . . . . . . . . . . . . . 6 24 and 36 V eXtreme Switch Inductive Switching 2 24 and 36 V eXtreme Switch Inductive Switching This paragraph explains dual high-side switch behavior during turn off, when the output is connected to an inductive load. 2.1 Clamped Inductive Switching (CIS) Figure 1. XS4200 and XSD200 Clamped Inductive Switching Schematic When turning off high-side switches on inductive loads, inductance polarity inverts and device output goes below ground to continue driving current. In the case of the 24 and 36 V eXtreme switch devices, the resulting negative voltage clamps to VCL (negative output voltage protection) via the internal clamping circuitry. This kind of inductive switching with no freewheeling diode is called the Clamped Inductive Switching (CIS). Load current is demagnetized by the internal power MOSFET only. The maximum load energy that can be drained is limited by device energy capability ECL. The energy dissipated in the MOSFET (ECL) during turn off depends on the load energy (Eload), on the power supply voltage and on the negative output voltage protection VCL. A simplified expression of ECL is given here: ECL= Eload * (1+ VPWR/|VCL|) = L * I²/2 * (1+ VPWR/|VCL|) Knowing that the energy dissipated in the MOSFET is higher than the load energy is important to consider when designing the module. However, for loads with L > 20µH, it is highly recommended to use a freewheeling diode. 2 Inductive Switching for Dual 24 and 36 V High-side Switch Families, Rev. 1.0 Freescale Semiconductor 24 and 36 V eXtreme Switch Inductive Switching 2.2 Inductive Switching with External Clamp > -2.0 V When turning off 24 and 36 V eXtreme switches on inductive loads >20 µH, using a freewheeling diode to drain the load current is highly recommended. Special care should be taken when designing the freewheeling path. As long as the output voltage of the device (VHS) is greater than -2.0 V (equivalent to the difference of the internal MOSFET threshold voltage with the forward voltage of the diode in gate driver clamping circuitry), current will flow through the freewheeling path. However, if the output voltage goes below -2.0 V, expect different behavior. Figure 2. XS4200 and XSD200 Inductive Switching with a Freewheeling Diode where VHS > -2.0 V 2.3 Inductive Switching with External Clamp < -2.0 V For high inductive loads, it is tempting to pull the device output down to help discharge the load more rapidly. Using additional devices in the freewheeling circuitry may allow this faster load demagnetization, but this can lead to higher energy through the MOSFET. When extra voltage is added in the freewheeling path, such as VHS < -2.0 V, the output voltage drops and the gate source voltage of the power die increases, creating a current path through the MOSFET. In this case, during turn off, load current is shared between the power MOSFET and the freewheeling circuitry. Special care should be taken when choosing components for the external circuitry, to limit energy in the power device to its maximum rating, indicated in the datasheet as ECL. Inductive Switching for Dual 24 and 36 V High-side Switch Families, Rev. 1.0 Freescale Semiconductor 3 24 and 36 V eXtreme Switch Inductive Switching Figure 3. XS4200 and XSD200 Inductive Switching with a Freewheeling Path where VHS < -2.0 V 4 Inductive Switching for Dual 24 and 36 V High-side Switch Families, Rev. 1.0 Freescale Semiconductor References 3 References Document Number and Description URL MC06XS4200 Dual 24 V High-side Switch (6.0 m) Data Sheet http://www.freescale.com/files/analog/doc/data_sheet/MC06XS4200.pdf MC10XS4200 Dual 24 V High-side Switch (10 m) Data Sheet http://www.freescale.com/files/analog/doc/data_sheet/MC10XS4200.pdf MC20XS4200 Dual 24 V High-side Switch (20 m) Data Sheet http://www.freescale.com/files/analog/doc/data_sheet/MC20XS4200.pdf MC06XSD200 Dual 36 V High-side Switch (6.0 m) Data Sheet http://www.freescale.com/files/analog/doc/data_sheet/MC06XSD200.pdf MC10XSD200 Dual 36 V High-side Switch (10 m) Data Sheet http://www.freescale.com/files/analog/doc/data_sheet/MC10XSD200.pdf MC16XSD200 Dual 36 V High-side Switch (16 m) Data Sheet http://www.freescale.com/files/analog/doc/data_sheet/MC16XSD200.pdf Inductive Switching for Dual 24 and 36 V High-side Switch Families, Rev. 1.0 Freescale Semiconductor 5 Revision History 4 6 Revision History Revision Date 1.0 2/2014 Description of Changes Initial release Inductive Switching for Dual 24 and 36 V High-side Switch Families, Rev. 1.0 Freescale Semiconductor How to Reach Us: Information in this document is provided solely to enable system and software implementers to use Freescale products. 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