Application Notes

Freescale Semiconductor
Application Note
AN4269
Rev. 1.0, 8/2011
eXtreme Switch
Diagnostic, Protection Features, and Limitations
By: Laurent Guillot and Juan Romero
1
Introduction
The purpose of this document is to provide an
overview of the diagnostic features offered in our
eXtreme Switch family, specifically for our
Generation 3 Quad high side drive devices
(MC10XS3412D, MC15XS3400D, MC10XS3435D
and MC35XS3400D). A description of the
diagnostic functionality, including it’s limitations
(especially at very low or very high duty cycles), will
be further developed.
This document is thought to extend on what the
data sheet already states, so consider the data
sheet as initial information. The values to be
presented in graphs, and throughout the document,
do not replace the parameters already specified in
our documentation. They are mainly to highlight
how certain parameters behave with changes in
temperature and supply voltage.
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Diagnostic and Protection Features . . . . . . . 2
2.1 Open Load in ON State (for Bulbs). . . . . . . 3
2.2 Open Load in ON State (for LEDs) . . . . . . . 4
2.3 Open Load in OFF State . . . . . . . . . . . . . . . 5
2.4 Short-circuit to VBATT . . . . . . . . . . . . . . . . 7
2.5 Short-circuit to GND . . . . . . . . . . . . . . . . . . 7
2.6 Current Sensing . . . . . . . . . . . . . . . . . . . . . . 8
2.7 Temperature feedback. . . . . . . . . . . . . . . . . 8
2.8 Under-voltage Detection . . . . . . . . . . . . . . . 8
2.9 Over-voltage Detection . . . . . . . . . . . . . . . . 9
© Freescale Semiconductor, Inc., 2011. All rights reserved.

Diagnostic and Protection Features
2
Diagnostic and Protection Features
Table 1 summarizes the diagnostic features offered within the extreme Switch family, which is
further explained in each of the sub-sections.
Table 1. eXtreme Switch Diagnostic and Protection Duty Cycle Limitations
Diagnostic and protection
features.
Low duty cycle limitation
High duty cycle limitation
Open load ON
Open load OFF
Short-circuit to VBATT
Short-circuit to GND
Current sensing
Temperature feedback
Under-voltage
Over-voltage
3.4%
0%
0%
3.4%
3.4%
0%
0%
0%
100%
86%
96%
100%
100%
100%
100%
100%
This table applies for:
• Bulb loads (200 Hz) with default slew rate selection
• LED
• loads (400 Hz) with fast slew rate selection
• with a 22 nF decoupling cap on the output
• 11 V  VPWR  18 V
• -40 to 125 °C ambient temperature
In case of a 100 Hz switching frequency (bulb load), the diagnostic limitations are reduced by half
of what is considered in Table 1 for 200 Hz. For example, the Open load ON low duty cycle
limitation of 3.4% at 200 Hz, would actually be 1.7% low duty cycle limitation at 100 Hz, since
both represent the same amount of detection time.
Diagnostic, Protection Features, and Limitations, Rev. 1.0
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Freescale Semiconductor
Diagnostic and Protection Features
2.1
Open Load in ON State (for Bulbs)
The internal mechanism used to detect an open load condition operates basically by monitoring
the amount of current flowing through the high side switch. When it is configured for regular
bulbs, the threshold would be at a typical 300 mA value. This detection circuitry integrates a
typical 4.0 µs filter, to properly recognize an open load condition in the ON state. Due to the
output transition from OFF to ON, it is not possible to detect an open load condition for a short
output pulse (low duty cycle). In this case, the open load in OFF state diagnosis can be used to
report this fault.
360
350
Current (mA)
340
330
320
310
300
290
‐40°C
25°C
125°C
Ambient Temperature (T A)
HS0_6V
HS0_20V
Figure 1. “Bulb” Open Load Current Threshold Variation in the ON State
Across Supply Voltage and Temperature
Diagnostic, Protection Features, and Limitations, Rev. 1.0
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Diagnostic and Protection Features
2.2
Open Load in ON State (for LEDs)
In the case of an open load when the ON state diagnostic is configured for LEDs, the detection
threshold is reduced to a typical 5.0 mA value. The detection concept (patented) is based on
initiating a controlled turn-off of the power MOSFET, together with a “weak” pull-up of the output
(a current source circuit is only activated for a short period of time, typically 150 µs, while in the
ON state). The behavior of the output voltage, compared to the gate voltage of the power
MOSFET, is evaluated during this time. If the output voltage is higher than the gate voltage during
this short period, it is recognized as an open load in the ON state condition.
5.3
5.25
5.2
"LED" open 5.15
load current 5.1
thresho ld (mA) 5.05
5
4.95
4.9
‐40°C
25°C
125°C
Ambient Temperature (T A) HS0_6V
HS0_20V
Figure 2. “LED” Open load in the ON State Current Threshold Variation
Across Supply Voltage and Temperature
Diagnostic, Protection Features, and Limitations, Rev. 1.0
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Diagnostic and Protection Features
2.3
Open Load in OFF State
This diagnostic operates differently from the previous two open load ON diagnostic features.
When the detection principle used is to allow a very small current (550 µA typical) to flow through
the load, just enough to pull the voltage at the output up for a very short period of time, during
this time, the voltage is measured. If the voltage is below a pre-defined 2.3 V typical threshold,
this condition is identified as an open load condition. To perform this diagnosis mechanism, a
certain amount of time is required, thus limiting the diagnostic capabilities at very high duty
cycles.
Figure 3 and Figure 4 are shown as a reference to illustrate the behavior of the threshold and the
source current variations at different temperatures and supply voltages. These graphs represent
the average value of tests performed in one lot of devices.
2.45
2.4
Open load OFF threshold (V)
2.35
2.3
2.25
2.2
‐40°C
25°C
125°C
Ambient Temperature (T A)
HS0_6V
HS0_20V
Figure 3. Open Load in the OFF State Threshold Variation Due to Temperature and Supply Voltage
Diagnostic, Protection Features, and Limitations, Rev. 1.0
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5
Diagnostic and Protection Features
58.0
058
57.5
058
57.0
057
057
56.5
Open load OFF 056
56.0
detection
55.5
056
source Current 055
55.0
(µA)
055
54.5
054
54.0
054
53.5
053
53.0
‐40°C
25°C
125°C
Ambient Temperature (TA) HS0_6V
HS0_20V
Figure 4. Open Load in the OFF State Detection Source Current Variation
Due to Temperature and Supply Voltage
Diagnostic, Protection Features, and Limitations, Rev. 1.0
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Diagnostic and Protection Features
2.4
Short-circuit to VBATT
To detect this condition, the voltage at the output is monitored in the OFF state. If the voltage is
higher than the pre-defined VOSD(THRES) threshold voltage, the output is reported to be a
short-circuit to VBATT. Since this measurement is done in the OFF state, the output needs to
remain in this state for a short time to be able to perform this diagnostic measurement. By using
this feature, it is possible to distinguish between a short-circuit to VBATT and an open load in the
OFF state.
Figure 5 shows in more detail how the VOSD(THRES) typical value varies with temperature and
supply voltage on each of the different outputs.
0.92
0.9
0.88
Output short to 0.86
Vpwr detection 0.84
voltage (VBatt‐ 0.82
voltage shown)
0.8
0.78
0.76
‐40°C
25°C
125°C
Ambient Temperature (T A)
HS0_6V
HS0_20V
Figure 5. VOSD(THRES) Variation Due to Ambient Temperature and Supply Voltage Variations
The voltage shown in Figure 5 is the voltage difference between VBATT and the output.
2.5
Short-circuit to GND
Detecting a short-circuit to GND is done by monitoring the high side MOSFET current. This
information is used to detect both a severe short-circuit condition or an overload of the high side
switch. This detection circuitry has a typical time filter of 3.0 µs, meaning that the output needs
to be turned ON for a minimum duration for this condition to be detected.
2.5.1
Severe Short-circuit to GND
During the OFF to ON transition of the output, the load impedance is compared to an internal
reference. Where the impedance is smaller than the internal reference, the output is turned OFF
without allowing the current to reach it’s maximum possible level. In this way, the thermal stress
inside the device is minimized.
This RSHORT value is guaranteed by design.
Diagnostic, Protection Features, and Limitations, Rev. 1.0
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Diagnostic and Protection Features
The duration of the OFF to ON transition depends on the characteristics of the short-circuit
(inductance, resistance, and ground shift).
2.5.2
Overload Current on the High Side MOSFET
The current monitored through the high side switch is compared with a level that changes
according to a selected over-current protection profile, and also with the amount of time the load
has been turned ON. This is explained in more detail in the application note AN4049.
2.6
Current Sensing
The current sensing functionality is explained in more detail in the AN3848 (MC15XS3400) and
the AN3853 (MC35XS3400) application notes.
2.7
Temperature feedback
In addition to the temperature sensors located on each of the different power MOSFETs, these
devices contain an additional temperature sensor, located on the “control die” and positioned on
top of the main ground terminal. This temperature is accessible to be read through the CSNS pin.
Different from the behavior of the current sense feedback, a proportional current to the load
current comes out of the CSNS pin. For temperature feedback, the output is a voltage that can
be directly read by an A/D pin from the MCU.
2.8
Under-voltage Detection
These devices contain a monitoring circuit for the supply voltage. If this voltage drops below a
pre-defined 3.85 V typical threshold, due to a long input line and severe-short circuit condition,
the outputs are automatically turned OFF before reaching the over-current level. The outputs are
automatically latched-OFF, in cases of an under-voltage condition.
Figure 6 shows the variation of the under-voltage threshold and it’s behavior vs. temperature.
Diagnostic, Protection Features, and Limitations, Rev. 1.0
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Diagnostic and Protection Features
4.10
004
4.05
004
4.00
004
3.95
004
Vpwr 3.90
004
undervoltage (V)
3.85
004
3.80
004
004
3.75
3.70
004
‐40°C
25°C
125°C
Ambient Temperature (TA)
Vpwr undervoltage lower level (Detection) VPWR(UV)
Vpwr undervoltage detection Upper level (Exit undervoltage condition) VPWR(UV)_Up
Figure 6. Under-voltage Detection Behavior Versus Temperature Variation.
2.9
Over-voltage Detection
If the supply voltage goes above a predefined 32 V typical threshold, the outputs are turned OFF.
The outputs will remain OFF until the over-voltage condition is removed (considering the defined
hysteresis of the detection circuit).
Figure 7 shows the variation of the over-voltage threshold and it’s behavior vs. temperature.
31.5
032
31.0
031
30.5
031
Vpwr overvoltage (V) 030
30.0
29.5
030
29.0
029
‐40°C
25°C
125°C
Ambient Temperature (TA) Vpwr overvoltage upper level (Detection) Vpwr(ov)
Vpwr overvoltage detection lower level (Exit overvoltage condition) [Vpwr(ov) ‐ Vpwr(ovhys)]
Figure 7. Over-voltage Detection Behavior Versus Temperature Variation
Diagnostic, Protection Features, and Limitations, Rev. 1.0
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AN4269
Rev. 1.0
8/2011
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