AN4858, Inductive Switching for Dual 24 and 36 V High-side Switch Families - Application Note

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
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© 2014 Freescale Semiconductor, Inc.
Document Number: AN4858
Rev. 1.0
2/2014
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