Features of the high-side family IPS70xx-P3-75V

Application Note AN- 1122
Features of the high-side family IPS70xx-P3-75V
By David Jacquinod
Table of Contents
Page
Introduction.......................................................................................... 2
Typical connection............................................................................... 2
Ground connection .............................................................................. 2
Diagnostic............................................................................................ 3
Open load detection when OFF........................................................... 3
Short circuit detection when ON .......................................................... 3
Over temperature detection when ON ................................................. 3
Protections .......................................................................................... 3
Current limitation-Temperature cycling................................................ 3
Ground loss protection ........................................................................ 4
Active clamp ........................................................................................ 4
Reverse battery ................................................................................... 6
Maximum voltage ratings..................................................................... 6
Recommended operating conditions ................................................... 6
Driving the high side for reliability ........................................................ 6
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Topics Covered
Inner Architecture
Typical connection
+Bat
+5V
• Introduction
• Diagnostic
Vcc
Rdgp
• Protections
• Active clamp and maximum inductive load
• Reverse battery
Typical Application
Dg
Control
Rdgs
V Diag
• Filament bulbs
In
R1
Out
Gnd
Rin
• Solenoids
Load
Input Signal
• Valves
Introduction
The new IPS70xx family of protected power MOSFETs
consists of five terminal high side devices based on the
3
latest IR proprietary vertical technology called P (Power
Product Platform) with 75V voltage capability. IR protected
MOSFETs are vertical power MOSFETs with integrated
protection circuitry. The new IPS70XX family features a
more efficient power MOSFET with active clamp and
integrated protections for over-temperature, current
limitation from over-current and active clamp.
IPS70xx family features a logic level input(IN), a logic
ground pin(GND) isolated from power GND and a
diagnostic pin (DG). An internal charge pump circuit allows
the MOSFET to be driven in a high side configuration
without the need of additional external components.
This application note explains the features of the high side
family, helps the designer to understand how it works and
provides suggestions on how to use these devices in the
automotive environment.
Figure 1 : Typical connection
Rin and Rdgs provide the protection for the controller
during reverse battery and negative pulses on Vbat. R1 is
required if the user want to use the open load detection.
Ground connection
+
Control
block
IN
Gnd
DG
Digital ground
-
Vcc
IPS
Out
Gnd
load
Power ground
The GND pin is the reference for the input and the DG pin
and should be connected to the digital ground of the
control block, so the load current does not flow into the
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digital ground. If the GND pin is connected to the power
ground, the load current will cause voltage difference in
the ground path and could shift the input threshold.
Diagnostic
Diagnostic features are used to communicate the status
of the IPS to the microcontroller. The IPS protects itself
against different kind of faults, such as: over current, over
temperature and open load. Once a fault condition is
detected by the IPS, the diagnostic information is made
available through a separate pin(DG). The truth table is
shown in Table1.
Operating Conditions
IN
OUT
DG pin
Normal
Normal
Open Load
(3)
Open Load
Short circuit to Gnd
Short circuit to Gnd
Over-temperature
Over-temperature
H
L
H
L
H
L
H
L
H
L
H
H
L(limiting)
L
L(cycling)
L
H
L
H
H
L
L
L
L
Protections
The IPS70xx family features protections in order to
prevent device failures during short circuit or over
temperature. After a fault condition is removed, the part
restarts automatically. During active clamp and reverse
battery there is no protection.
Current limitation-Temperature
cycling
When the output is shorted to ground, the device limits
the current by driving the MOSFET into linear mode. The
power dissipation is high in this mode, so the temperature
protection will stop the device. The device will restart
when the junction temperature cools down by 7°C.
Vin
Iout
limiting
Ilim
Thermal cycling
Table 1. Diagnosis truth table
(3)
With a pull-up resistor connected between the output
and Vcc.
Open load detection when OFF
There are cases in which the detection of an open-load is
requested also when the load is OFF. In this case the
micro-controller is aware of the open load as soon as it
happens.
The IPS can detect this condition as well, but an external
pull-up resistor is needed.
When the power MOSFET is OFF the open load condition
is detected by comparing the OUT voltage to the GND. In
the normal condition, the load is connected to GND and
no current (beside the output leakage) flows into the load.
The Source voltage will be almost zero. If the load is
disconnected, an external resistor pulls-up the output so
that the open load condition is detected by an integrated
comparator.
Tj
Tsd+
Tsd-
DG
Figure 2: Protections timing diagram
The current limitation and the over-temperature must only
be used for protection. In normal mode, these protections
must not be triggered, otherwise the reliability of the
device will be affected. For example, the inrush current of
the load must be lower than the current limit.
Short circuit detection when ON
When the part is on, the diagnostic detects a short circuit
because Vbat - Vout is higher than the short circuit
detection voltage(Vsc in the datasheet).
Over temperature detection when
ON
The over temperature condition is detected when the
input is high by a thermal sensor.
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Figure 3 : Turn on a short circuit
CH1: Input, CH3 : I load 10A/div
Ground loss protection
When the ground is disconnected, the device is
automatically switched off in order to prevent any failure.
The two parasitic bipolars between input and drain pins
and diagnostic and drain pins may turn on and current will
flow from the drain to the microcontroller. Rdgs and Rin
limit the current in order to protect the IPS and the
microcontroller.
Input current into the Microcontroller
Dg
Vcc
In
Out
Gnd
Vclamp
L
5V
Vin
0V
Vout
Rem :
During active
clamp, Vload
is negative
+
14V
-
R
Iout
+Bat
Vcc
+5V
Figure 5 : Active clamp circuitry
Micro
Rdgp
Rdgs
Dg
In
Gnd
Out
Rin
Load
Active clamp methodology
One way to control the VDS of a MOSFET is by driving it
in the linear region. A feedback loop inside the IPS,
allows regulation of VDS to the targeted active clamp
voltage by adjusting the output MOSFET gate voltage
independently of the load current. The internal circuitry
consists of a zener diode connected between drain and
gate and a resistor from gate to ground. Note that during
active clamp the output MOSFET is driven in the linear
region and the power dissipation does not depend on the
RDSON.
T clamp
Vin
Figure 4 : Ground loss protection
Active clamp
During active clamp, the current is controlled by the load.
So no protection ( temperature or current ) is active
during this mode. The designer must check such that in
the worst condition of current and temperature, the power
dissipated during the turn off is within the SOA of the IPS.
Purpose of the active clamp
When switched OFF, an inductive load generates a
voltage across its terminal whose amplitude depends on
the current slope and the inductance value. In a high side
configuration the over voltage across the inductance will
make the drain-to-source voltage rise above the battery
voltage. This would cause the body diode to go into
avalanche, if no external zener clamps or freewheeling
diodes are used, as shown in figure 5.
The purpose of the active clamp is to limit the voltage
across the MOSFET to a value below the body diode
break down voltage to reduce the amount of stress on the
device during switching.
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Ids
Vcc
Vds
Vds clamp
Figure 6 : Active clamp waveforms
Energy consideration when using active clamp
Active clamp allows faster recirculation compared to free
wheeling techniques, and it does not require the use of
external devices. The drawback of the active clamp
technique is that the energy is dissipated by the IPS. The
energy must be evaluated to ensure safe operation of the
IPS. Energy dissipation calculations are shown in the
following section:
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Energy dissipated by the IPS:
EIPS =
VCLAMP
1
⋅ L ⋅ I2 ⋅
2
VCLAMP − VBATT
100
Energy dissipated by the load:
1
⋅ L ⋅ I2
2
Since VCLAMP must be higher than VBATT the IPS dissipates
more energy than the load. This is due to the fact that
during active clamp some energy is taken from the
battery.
In order to minimize the energy dissipation on the IPS the
VCLAMP must be as high as possible, compatibly with the
breakdown voltage of the technology. The IPS70XX
family has a typical active clamp voltage of 70V.
The energy dissipated by the IPS is proportional to the
load inductance and the square of the load current.
Curves similar to figure 7 are given in the data sheet.
They allow the estimation of the maximum load
inductance vs. the load current, based on the amount of
energy that can be dissipated by the IPS.
Note that the load ‘parasitic resistance’ provides a
limitation to the load current. Maximum load current must
be calculated in the worst possible supply conditions. For
example with a 100uH load, the curve shows a maximum
Iload = 12A. If the worst-case VBATTERY is 18V, the
inductor minimum series resistance must be 18V/12A=
1.5 Ohm, according to figure 7.
10
1
0.001
0.01
0.1
1
10
Figure 7 : Max. Output current (A) vs.
inductive load (mH)
Temperature increase during active clamp
The energy dissipation during active clamp will cause the
junction temperature to increase.
The temperature increase during active clamp can be
estimated as follows:
∆ Tj = PCL ⋅ Z TH ( t CLAMP )
Where: Z TH ( t CLAMP ) is the thermal impedance at tCLAMP
and can be read from the thermal impedance curves
given in the data sheets.
PCL = VCL ⋅ ICLavg : Power dissipation during active clamp
VCL = 70V : Typical VCLAMP value for the IPS70xx
ICLavg =
t CL =
ICL : Average current during active clamp
2
ICL : Active clamp duration
di
dt
di VBattery − VCL : Demagnetization current
=
dt
L
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The temperature increase during active clamp must be
limited by design to avoid damaging the IPS.
Reverse battery
In the reverse battery condition, the designer should be
aware that no other protection is available. So in the
worst case condition of temperature and voltage, the over
temperature threshold should not be reached. The current
will flow from In, Dg, Gnd and Out pin to Vcc pin.
Current path in reverse battery
+Bat
Vcc
+5V
Rdgp
Rdgs
Maximum voltage ratings
Maximum Vcc voltage
This is the maximum voltage before the breakdown of IC
process.
Maximum continuous Vcc voltage
This is the voltage used during the qualification.
Recommended operating
conditions
These are the operating conditions for the key
specifications, under which the device is recommended to
be operated. Typically, the recommended operating
conditions define limits for device operation under steady
state conditions. The absolute maximum rating provide
the limits for worst case conditions, such as transient.
Driving the high side for reliability
Dg
In
Gnd
Out
Rin
Load
Figure 8: Current paths in reverse battery
conditions
The reliability rules for the IPS are the same as for a
MOSFET. A high variation of junction temperature
decreases the life expectancy. During thermal cycling, the
variation of the junction temperature is 7°C. But if the
system switches off the device for a long time before
restarting it, the junction temperature variation will be
higher.
If autorestart is required, the controller should maintain
the device in thermal cycling. If the controller must switch
off, the number of retries must be limited to guarantee a
high level of reliability.
Current through the output pin
The current would normally flow through the load into the
body diode of the MOSFET during reverse battery. The
power dissipation in the IPS can be estimated as
Pd IPS = V f ⋅
VBATT
RLOAD
where Vf is the forward voltage drop of the MOSFET
body diode (typical 0.7V).
Current through In and Diag
Resistors in series with the terminals (In and Diag) will
limit the current in the IPS. A typical value for these
resistors is 7.5KΩ.
Current through GND
Current through the GND terminal can be very high since
no external components can be placed on this terminal. A
schottky diode should be inserted in the positive Vcc line.
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