3731 High Side Drivers

8/4/2019 3731 High Side Drivers

1/24

APPLICATION NOTE

by A. RussoB. Bancal

J. Eadie

INTRODUCTION

The ever increasing demand for cost

reduction and higher levels of circuitcomplexity and reliability have directed thesemiconductor manufacturers attention

towards smart power technologies which

allow the production of totally integrated

monolithic circuit solutions that include apower stage, control, driving and protectioncircuits on the same chip.

HIGH SIDE DRIVERS

power transistor on the same chip. Thepower handling capability of this type ofstructure compares favourably with

monol i th ic smart power dev ices ofequivalent chip size which use lateral, or"U-turn" power output structures.

Vertical intelligent power, (VIPower TM) anSGS-THOMSON Microelectronics patentedtechnology, established over 7 years ago,

uses a fabrication process which allows theintegration of complete digital and/oranalog control circuits driving a vertical

1/24AN514/1092


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3/24

voltage shutdown feature. It is simple to

introduce some differences in the controllogic to produce devices with features

w h i c h c a t e r f o r d i f f e ren t w o rk i ngenvironments.

Each application exerts an externalinfluence over the switch. A filament lampor DC motor, for example, have in-rush

currents that any switch has to handle.Solenoids and motors have an inductiveef fec t and must lose the res idua l

magnetism when the current is turned off.This gives rise to induced voltages and the

need to remove this stored energy.External fault conditions can also stressthe drivers and their associated circuitry.The fo l lowing discuss ion has been

designed to explain the basic principlesinvolved in using these devices and tohelp to understand how they react

under the influence of various applications.

Almost every electronic switch used in amodern automobile application is a high

side switch. This configuration ispreferred for automotive use because:

a) - This configuration protects the loadfrom continuous operation and resultingfailure, if there is a short circuit to theground. Since the body of a car is metal

and 95% of the total car is ground, theshort to ground is much more commonthan short to V

CC

b) - High Side Drivers cause lessp rob l em s w i t h e l ec t r oc hem i c a lcorrosion. It is of primary importancein automotive systems because the

electrical components are in an adverseenvironment, specif ically adversetemperatures and humidity and the

presence of salt. For this reason theseries switch is connected between theload and the positive power source.

Therefore when the elect r ical

component is not powered (that is for

the greatest part of the lifetime of thecar) it is at the lowest potential and

electrochemical corrosion does not takeplace.

Integrated High Side Dr ivers of fer

numerous advantages over the popularautomotive relay used in cars today.Diagnostic information output from the

High Side Driver helps the on-boardmicrocontroller to quickly identify andisolate faults saving repair time and often

improving safety. High Side Drivers can

reduce the size and weight of switchmodules, and where multiplexed systems

are used, dramatically reduce the size ofthe wiring harness.

Process control applications offer anotheruse for High Side Drivers. A considerableimprovement in reliability and reduction in

down time can be obtained by using themin place of relays. Process controlsystems, often consisting of powerful

computers that control large numbers ofactuators, are perfect environments forthese dev ices . The semiconduc tor

manufacturer has little control over thenature of the load being driven and thesecan vary - solenoids, motors, transducers,

leds. In these situations, software processmonitoring by a P can detect a faultreported by a status output and offers the

option of taking corrective action. In theunlikely event of a failure in a High Side

Driver in critical processes, a seconddevice can be programmed to operateinstead.

SGS-THOMSON High Side Drivers aredesigned to provide the user with simple,self protected, remotely controlled power

switches. They have the general structureas shown in figure 1. Appendix I shows atable of the devices and summarizes their

features.

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APPLICATION NOTE


4/24

Figure 1 : Standard current and voltage conventions

THE GENERAL FEATURES OF HIGHSIDE DRIVERS.The diagram in figure 3 shows the control

and protection circuit elements and the

power stage of a basic device.

Figure 2 : High Side Drivers interfaces between control logic and power load

Some typical applications are shown in figure 2.

4/24

APPLICATION NOTE


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Figure 3 : Generic Internal Block Diagram

Input

The 5V TTL input to these High SideDrivers is protected against electrostaticdischarge. General rules concerning TTL

logic should be applied to the input. Theinput voltage is clamped internally at about

6V. It is possible to drive the input with ahigher input voltage using an externalresistor calculated to give a current notexceeding 10mA at the input.

Internal power supplyTo accommodate the wide supply voltagerange experienced by the logic and controlfunctions, these devices have an internal

power supply. Some parts of the chip areonly active when the input is high, the

status output and charge pump forexample. This means it is possible toconserve power when the device is idle.The internal power supply has therefore

been designed in two parts. One sectionsupplies power to the basic functions ofthe chip all the time, even when the input

is 0V. The second section supplies poweronly when the input is high. This ensuresthat the stand-by current is limited to 50Amaximum in the off-state.

THE CONTROL CIRCUIT.Under voltage lock-out.

Under-voltage protection occurs when the

supply voltage drops to a low levelspecified in the datasheet as V

USD. The

under-voltage level set at this value

ensures the device functions correctly.Inductive effects must be considered inunderstanding the function of this feature.

The di/dt is controlled by the device andnot by the external circuit. The controlledvalue is calculated for a line inductance of

5H( 5mt. of wire). Typically di/dt=0.5A/sfor a normal load and 1A/s for a shortcircuit. At turn on this generates an

opposing voltage. If this opposing voltageis too large, the apparent supply voltage

will drop below the under-voltage lock-outlevel and the device will turn off. Usingthe specified conditions, the inducedvoltage will not be large enough to reduce

the supply voltage below 6V. This isimportant in the case where the load is anear short circuit when in-rush currentoccurs, as in the case of a car headlamp

filament turning on.

* Optional feature in the VNXXAN series

5/24

APPLICATION NOTE


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Open load detection and stuck-on toV

CC.

Open load detection occurs when the load

becomes disconnected. In the VN20Nfamily open load detection only occurs in

the on-state.

An extra feature for load disconnection

detection is that open load detection duringthe off-state as well as in the on-state can

be provided. The circuit for the off-stateopen load detection requires an externalresistor between V

CCand the output pin.

Figure 4 : Equivalent Schematic for the open load detection current in off-state

Over-temperature protection

Over-temperature protection is based onsensing the chip temperature only. The

location of the sensing element on the chip

in the power stage area, ensures that

accurate, very fast, temperature detectionis achieved. The range within which

overtemperature cutout occurs is140C - 180C with 160C being a typicallevel.

Over-temperature protection acts to

protect the device from thermal damageand consequently also limits the averagecurrent when short circuits occur in the

load.

Open load detection is possible in the off-

state in the VN21 family and it conforms

to the I .S.O. norms for automotiveapplications. If an open load condition is

detected the status flag goes low. Shouldan external supply be applied to the load(output pin) or the device is externally short

circuited, the off-state open load detectioncan detect this stuck-on to V

CCcondition.

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APPLICATION NOTE


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Figure 5 : VN20N Die Layout - Note the thermal sensor inside the Power MOSFET Area

Driving the power MOSFET.The power MOSFET output stage is drivenby an internally generated gate voltage. Acharge pump provides sufficient voltage to

turn on the gate.

Turn-onAs previously explained, the High Side

Drivers are turned-on with a controlled

di/dt.

Turn-off: Normal and fast loaddemagnetizationWhen a High Side Driver turns off an

inductance a reverse potential appearsacross the load. z

Figure 6 : Inductive load demagnetization turn-off for the VN20N family

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APPLICATION NOTE


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The source of the power MOSFET

becomes more negative than the groundunti l i t reaches the demagnetization

voltage, Vdemag., of the specific device. Inthis condit ion the induct ive load isdemagnetized and its stored energy isd i ss ipa ted i n t he power MOSFET

according to the equation shown below:

VN20N VN21

In the basic High Side Driver family the

typical value of, Vdemag. is = 4V.

In the I.S.O. and industrial series,to reducethe dissipated energy, an internal circuithas be added in order to have a typical

Vdemag. = 18V.

In this condition the stored energy is

removed rapidly and the power dissipationin the power MOSFET is reduced - seeequation. Figure 7a/b compares thewaveforms of the normal and fast

demagnetization techniques.

Figure 7a/b : VN20N-VN21 Driving an Inductive Load

[Vcc

+Vdemag.

]P

demag.= 0.5 L

load[I

load] ------------------- f

Vdemag.

where f is the switching frequency and

Vdemag.

the demagnetization voltage.

Figure 7b shows the VN21 driving aninductive load. During the on period, the

current in the load rises linearly to amaximum. At turn-off the current decrease

linearly, but, at a sufficiently fast rate forfast demagnetization of the load. Thereis no fault output from the status pin. Inthe VN20N, the basic High Side Driver

w i t h no s pec i a l f ea t u re f o r f as tdemagnetization, the turn-off takes up to 5times longer than the VN21. Note that the

status output will pulse at turn on becausethe internal circuit detects a very shortduration open load, see figure 7a.

The maximum inductance which causes

8/24

the chip temperature to reach the shutdown temperature in a specified thermal

environment, is a function of the loadcurrent for a f ixed V

CC, V

demag.and

switching frequency. This is the maximumra te a t wh ich the d r i ve rs can bedemagnetized. Figure 8 shows themaximum inductance for a given load

current for dev ices meet ing I .S.O.requ i r em en t s , as s um i ng a c h i ptemperature of 160C at turn-off and a

supply voltage of 13V. The values are fora single pulse with 85C case temperature.Note that the devices are not protected

against overtemperature during turn-off.

APPLICATION NOTE


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Figure 8 : Max inductance which produces a temperature of 160C at turn off with Vcc = 13V.The values are for a single pulse with Tc = 85C

Additional Features of the High SideDriversHigh Side Drivers are designed for use in

various market segments, the preciserequirements of the drivers varying a littlewith the application. There are additional

f ea t u res t o ac c om m oda t e t hes erequirements.

To reduce the on-state quiescent currentfor some applications, particularly industrialones, the open load detection circuit is not

included. There will consequently also be alower power dissipation, an important pointwhen similar, multiple High Side Drivers

are mounted on one board. It can meansthe difference between using or not usinga heatsink.

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CONDITIONS: VCC = 13V TC = 85C

APPLICATION NOTE


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The operating voltage range can vary e.g.

5.5V to 26V for automotive applicationsand 7V to 36V for process control. Some

devices have fast demagnetization of theload, ground disconnection protection,on- and off- state open load detection and5ms filtering of the status output.

Status output and status output signalfiltering.The difference in electrical behaviourbetween the non-filtered and the filtered

High Side Drivers is that the status outputfiltering circuit provides a continuous signal

for the fault condition after an initial delayof about 5ms in the filtered version. Thismeans that a disconnection during normaloperation, with a duration of less than 5ms

does not affect the status output. Equally,any re-connection during a disconnectionof less than 5ms duration does not affect

the status output. No delay occours for thestatus to go low in case of overtemperatureconditions. From the falling edge of the

input signal the status output initially low in

fault condition (overtemperature or openload) will go back high with a delay t

POVLin

case of overtemperature condition and adelay t

POLin case of open load. These

features fully comply with InternationalStandards Office, (I.S.O.), requirements for

automotive High Side Drivers.

ABNORMAL LOAD CONDITIONS:

Load short circuits

Should a load become short circuited,various effects occur and certain stepsneed to be taken to deal with them,

particularly choosing the correct heatsink.Two clear cases of short circuit occur:

1. The load is shorted at start-up.

2. The load becomes short during

the on-state.

Start-up with the load short circuited.At turn-on the gate voltage is zero and

begins to increase. Short circuit currentstarts to flow and power is dissipated in theHigh Side Driver according the formula:

Pd

= VDS

x ID

The effect is to cause the silicon to heatup. The power MOSFET stays in the linear

region. When the silicon temperaturereaches about 160C the over temperaturedetection operates and the switch is turned

off. Passive cooling of the device occursuntil the reset temperature is reached andthe device turns back on again. The cycle

is repetitive and stops when the power isremoved, the input taken low or the shortcircuit is removed.

Figure 9 : Automatic Thermal cycle at start - up with the load short - circuited.

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APPLICATION NOTE


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Even in this configuration, the device

controls the di/dt. Figure 9 shows astart-up when there is a short circuited load

driven by a VN05N. The initial peak currentis 30A for this 180m device.

A short circuit occurring during the on-state.When a short circuit occurs during the

on-state, the power MOSFET gate is

already at a high voltage, about VCC

+ 8V,so the gate is hard on. Hence the short

circuit di/dt is higher than in the first case,and only controlled by the load itself. Afterthe steady state thermal condition isreached, thermal cycling is the same as in

the previous case.

Figure 10 : Automatic thermal cycle for a short circuit occouring during the on - state

The thermal cycling in overload conditionsproduces repetitive current peaks. Thedevice switches on, the silicon heats up

until the over-temperature sensing acts to

Figure 11 : Automatic Thermal cycle in overload condition

Automatic thermal cycle.turn the device off. The rate of passivecooling depends on the thermal capacity ofthe thermal environment. This, in turn,

determines the length of the off-stateduring thermal cycling.

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APPLICATION NOTE


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It is important to evaluate the average andRMS current during short circuit conditions.This is required in order to determine the

track dimensions for printed circuit boardsand the correct value for any fuse used.In all practical situations there is no danger

to pcb tracks from these high peak currentfor track designed to handle the nominalload current.

Evaluating the Average current

In steady state conditions the junctiontemperature osc i l la tes between T j

(shutdown) and Tj (reset).

Tj(av.)=(Tj(shutdown)+Tj(reset))/2 135C

Dissipated power:

PD

= I(AV)

x VCC

For a specific package

PD

= (TJ(AV)

- Tcase

) / Rthj-case

I(AV)

=(TJ(AV)

- Tcase

) / (Rthj-case

x VCC

)

Evaluating the RMS currentThe RMS current, I

RMS, generates heat in

the copper track on PCBs during shortcircuits.

T

I(RMS)

2 = 1/T0

I2(t)dt

I(RMS)

= I(PK)

x/T, where /T is the duty cycle.

T

with I(AV)

= 1/T0

I(t)dt = I(PK)

x /T

I(RMS)

= (I(PK)

x I(AV)

)

Note that Iaverage

does not depend on thepeak current I

(PK).

Example:

VN21 with Tcase

= 85C has an average

current, I(AV)

= 3.85A,

at Rthj-case = 1C/W and VCC = 13VThe average current is independent of thepeak current.Generally, a current limiter does not

decrease the average current.

Figure 12 : Average current during an hard short - circuit test

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APPLICATION NOTE


13/24

The RMS current increases proportionally

to the square root of the peak current -->+40% if I

(PK)is doubled. Schemes to limit

the current do not decrease the RMScurrent significantly.

Heatsink requirements.Overload protection is based on device

heat ing. I f you want to detect anoverload, i.e a damaged load, the chip

must be allowed to heat up so that thethermal sensor located on the chip isactivated. This leads to the following

general rules for sizing heatsinks for theVN High Side Drivers.

1.Do not use a too big heatsink.2.Do not use a VN device which has

RON

much lower than that which

the application requires.

This example illustrates a specific case.

Situation:

- a supply voltage of 14V,

- a load resistance of 2,- VN20N - R

DS(on)at 25C = 50m

- load current = 7A

To detect an over current of 20A,

Figure 13 : RMS current during an hard short-circuit test

13/24

assuming that RDS(on)

at 150C = 100m

(see datasheet) hence:

PD

= (20)2 x 100 x 10-3 = 40W

Rthj-a

should be dimensioned for

thermal shutdown

- Ambient

< PD

x Rthj-a

.

For example 160C - 25C < 40W x Rthj-a

The effects of load disconnection.When a load becomes disconnected there

can be over-voltages caused by thechange of load current. Figures 14a/bsummarizes the likely effects. Figure 14a,

shows a load driven by a VN21. The supplyto the VN21 has a very low parasiticinductance. When the load becomes

disconnected, the current changes at arate determined by the time taken for theload to disconnect. This controls di/dt .

APPLICATION NOTE


14/24

Figure 14a/b : Example of possibles situations during a load disconnection

Figure 14c : Behaviour of a VN21 during a load disconnection

connection pins are likely to have someinductance, to use a 56V zener diode or a

capacitor close to the supply pin of theswitch. Figure 14c shows a test madeusing a zener clamp to overcome line

inductance.

PROTECTION AGAINST GROUNDDISCONNECTION

There are a number of distinct situationsthat can occur when one of the groundconnections is broken in circuits using the

High Side Drivers.

The first case, shown in fig. 15a, is when

the GND pin of the High Side Driver is

In this present case, there is virtually noinductance in the supply line. Hence no

over-voltage is generated and Vcc

isunaffected. The status pin goes low toindicate an open-load state

In the second case illustrated, figure 14b,

the supply line has parasitic inductanceand capacitance. When the load isdisconnected an over-voltage is generated,

(Vover-voltage

= L di/dt). The di/dt is notcontrolled by the device but by how fastthe load is disconnected. It is possible that

the over -vo l t age may exceed thebreakdown voltage of the device. It is aw ise precaut ion where the supply

14/24

TEST CONDITIONS: LINE INDUCTANCE +++++ 46 VOLTS CLAMPING DEVICE

APPLICATION NOTE


15/24

disconnected while the C and the loadare connected to ground. In this case inthe I.S.O. and industrial High Side Drivers

nothing happens and the device remainsoff. In the VN20N family a voltage of about

2V appers on the load and conseguentlythere is a power dissipation:

PD

= (VCC

- 2) ILOAD

usually very low. In these conditions thediagnostic is not functioning.

Figure 15a : Possible ground disconnection occurring when a High Side Driver is connected toa Controller (case 1)

state at VCC

. In the VN20N family a voltage

of about 4V appears on the load andconseguently there is a power dissipation:

PD = (VCC - 4) ILOADIf P

Dis excessive with respect to the

heatsink capability, destruction may occurs

since the protections are not functioning.The load is permanently activated.

The second case, shown in fig. 15b, iswhen both the GND pins of the High SideDriver and of the C are disconnected

while the load is connected to ground. Inthis situation the signal GND rises up toV

CC. In the I.S.O. and industrial High Side

Drivers nothing happens up to VCC


16/24

Another practical case is when an external

component supplies current to the HighSide Driver GND pin which is disconnected

from the ground. This might occur if theVN device is mounted on a local PCB withother devices and has a local ground whilethe load may be grounded to the frame or

body of the equipment, figure 16. Also, inthis case, for internally protected devices,the output remains off up to the pointwhere the voltage on the GND pin is 18Vwith reference to real ground at 0V. Thiswill reduce the maximum V

CCthe High Side

Driver is able to withstand before turningon with the control circuit in-operative.

One solution to this problem is to insert a

resistor and diode in between the deviceGND pin and the output pin. The series

resistor, Rs, must be calculated so that thesum of the current, Is, of the High SideDriver chip connected to the GND node

plus the current drawn by the externalelements, produces a voltage drop of lessthan 18V across Rs + Ds + R

loadfor I.S.O.

or industrial High Side Drivers and lessthan 2V for STD devices.

CONCLUSION

The VN series of High Side Drivers offersdesigners a highly attractive method of

controlling a variety of inductive andresistive loads. The option to use aselection of extra features such as fast

demagnetization or status filtering makesthem equally suitable for general orspecialised use, typically in the automotive

environment.

Figure 16 :Ground disconnection occuring when an equivalent resistor supplies current on the GND pin.

16/24

APPLICATION NOTE


17/24

60V B(BR)DSS

HIGH SIDE DRIVERS PRODUCT RANGE

VIPower

VN02NVN05N

VN20NVN30N

VN03

VN06VN21VN31

DEVICE RDS(on)

@ 25C(mohm)

400

1805030

500180

5030

VCC

Range(V)

7 - 267 - 267 - 26

7 - 26

5.5 - 26

5.5 - 265.5 - 265.5 - 26

Pentawatt/PowerSO-10TM

"""

PACKAGE

Pentawatt/PowerSO-10"

""

EXTRAFEATURES

35050

7 - 367 - 36

Pentawatt/PowerSO-10"

VN02ANVN20AN

200100

60

6 - 26

6 - 26

6 - 26

Heptawatt/PowerSO-10"

Pentawatt/PowerSO-10

VN02H(*) 400 5 - 36 Pentawatt/PowerSO-10

VND05B(*)

VND10B(*)

VN16B(*)

(*) Application information as described in the Note apply also to these devices

Open load detection off state + stuck-on to VCC

Fast demagnetization & ground disconnection protection

5msec STATUS FILTERING (ISO STANDARD)

17/24

Double channel

APPLICATION NOTE


18/24

SCHEMATIC

COMPONENT

VN03

VN06

VN21

VN31

REXT

Ifthelineinductanceisnot

zeroanddi/dtcausedby

disconnectionoftheload

ishigh,anovervoltageE

=Ldi/dtappearsonVCC,

TheV(BR)DSS

oftheoutput

powerMOSFETcouldbe

exceeded.

D4orC1

D4orRLIM

Itisnecessarytosetthe

currentthatfixes

the

voltage,VLOAD,intheoff

state.WhenRLOAD

fails-

goes

open

or

high

resistance-VLOADincreases

andaninternalcomparator

triggersthestatusflagtogo

low.

COMMENT

RLOAD


19/24

19/24

VSS=GND

Nocurrentaccross

input

ADCcurrentflows

inthe

Iftheloadisaninductancewith

aparallelfreewheeling

diode,

theusersees2forwardbiased

diodesbetweenGROUN

Dand

Donotexceedimaxto

Ifthebatteryisshortcircu

itedby

3x2seriesdiodes(typic

allyan

alternatordiodeconfigu

ration)

CC,

is

clampedtoabout-3Vandno

damageoccurstotheVN

device.

forthedeviceis-13V.To

preventdamagetothedevice

use

either

a

bipol

ar

or

diodeinserieswiththeg

round

pinconnection.UseR

1and

R2tolimitthenegativec

urrent

intheinputandstatuspins

becausetheinternalg

round

SCHEMATIC

COMPONENT

COMMENT

NOTES

ALL

*VCC

>1V

MGND"ON"

Normalcase

*-4VSS1

VIL

andVIH

shiftedby(VSS2

-

VSS1).R1limitsa

nynegative

currentwhenthe

Controller

takesI/O

toground.Onthe

statuspinthezerocorresponds

totheVF

ofD2,V

USD

andVOL

beingincreasedby(VSS2-GND).

R

2,D2

Usingadiodetoprotectthe

Cagainstreversedbattery.

VSS1=/=VSS2.

VSS2VCC.

AcurrentwillflowoutofGND

pin,possiblydamagingthe

bonding.

ALL

D1

High

voltages

can

be

generatedifthebatteryis

disconnected

when

the

generatorisrunninginacar.

Damagingeffectscanbe

overcome

by

using

a

clampingdiodewithatleast

VBR

>

26V

as

2

x

12V

batteriesareoftenusedto

jumpstartcars.Thisfor

overvoltagetransienthigher

thanspecifiedindatasheets.

Protectionagainstover-voltages

are

efficientifconnected

betweenpin3(V

CC)andpin1

(ground).

ALL

Insert

a

resistance,

R1

(suggestedvalue

47),inthe

groundpintolim

ittheground

currentandavoid

damagingthe

bonding.

DEVICE

Load

dump:

battery

disconnectionwhilstthe

alternatorisworking

16

VLOAD

>VCC

(Bridgecircuit)

17

SYMPTOM

NOTES

APPLICATION NOTE


24/24

APPLICATION NOTE

24/24

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3731 High Side Drivers