APPLICATION NOTE

by A. RussoB. Bancal

J. Eadie

INTRODUCTION

The ever increasing demand for costreduction and higher levels of circuitcomplexity and reliability have directed thesemiconductor manufacturer’s attentiontowards smart power technologies which

allow the production of totally integratedmonolithic 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 withmonol i th ic smart power devices 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

The VIPower technology M0 used formaking these High Side Drivers producesa monolithic silicon chip which combinescontrol and protection circuitry with a

standard power MOSFET structure wherethe power stage current flows verticallythrough the silicon.

CROSS SECTION OF MØ VIPower TM TECHNOLOGY

High Side Drivers, with their integratedextra features are power switches that canhandle high currents and work up to about40V supply voltage. They require only asimple TTL logic input and incorporate afault condition status output. They can

drive an inductive load without the need fora freewheeling diode. For completeprotection the devices have an over-temperature sensing circuit that will shutdown the chip under over-temperatureconditions. They also have an under-

SMART POWER APPROACHES

2/24

Driving circuitry

Power stage output

Enhancement and depletion NMOS

Power stage

VDMOS

APPLICATION NOTE

voltage shutdown feature. It is simple tointroduce some differences in the controllogic to produce devices with featureswh ich ca te r f o r d i f f e ren t wo rk ingenvironments.

Each application exerts an externalinfluence over the switch. A filament lampor DC motor, for example, have in-rushcurrents that any switch has to handle.Solenoids and motors have an inductiveef fec t and must lose the res idua lmagnetism when the current is turned off.This gives rise to induced voltages and theneed to remove this stored energy.External fault conditions can also stressthe drivers and their associated circuitry.The fol lowing discussion has beendesigned to explain the basic principlesinvolved in using these devices and tohelp to understand how they reactunder the influence of various applications.

Almost every electronic switch used in amodern automobile application is a highside 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 metaland 95% of the total car is ground, theshort to ground is much more commonthan short to VCC

b) - High Side Drivers cause lessp r o b l e m s w i t h e l e c t r o c h e m i c a lcorrosion. It is of primary importancein automotive systems because theelectrical components are in an adverseenvironment, specif ically adversetemperatures and humidity and thepresence of salt. For this reason theseries switch is connected between theload and the positive power source.Therefore when the electr ical

component is not powered (that is forthe greatest part of the lifetime of thecar) it is at the lowest potential andelectrochemical corrosion does not takeplace.

Integrated High Side Dr ivers of fernumerous advantages over the popularautomotive relay used in cars today.Diagnostic information output from theHigh Side Driver helps the on-boardmicrocontroller to quickly identify andisolate faults saving repair time and oftenimproving safety. High Side Drivers canreduce the size and weight of switchmodules, and where multiplexed systemsare used, dramatically reduce the size ofthe wiring harness.

Process control applications offer anotheruse for High Side Drivers. A considerableimprovement in reliability and reduction indown time can be obtained by using themin place of relays. Process controlsystems, often consisting of powerfulcomputers that control large numbers ofactuators, are perfect environments forthese dev ices. The semiconductormanufacturer has little control over thenature of the load being driven and thesecan vary - solenoids, motors, transducers,leds. In these situations, software processmonitoring by a µP can detect a faultreported by a status output and offers theoption of taking corrective action. In theunlikely event of a failure in a High SideDriver 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 powerswitches. They have the general structureas shown in figure 1. Appendix I shows atable of the devices and summarizes theirfeatures.

3/24

APPLICATION NOTE

Figure 1 : Standard current and voltage conventions

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

Figure 3 : Generic Internal Block Diagram

InputThe 5V TTL input to these High SideDrivers is protected against electrostaticdischarge. General rules concerning TTLlogic should be applied to the input. Theinput voltage is clamped internally at about6V. 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 internalpower supply. Some parts of the chip areonly active when the input is high, thestatus output and charge pump forexample. This means it is possible toconserve power when the device is idle.The internal power supply has thereforebeen designed in two parts. One sectionsupplies power to the basic functions ofthe chip all the time, even when the inputis 0V. The second section supplies poweronly when the input is high. This ensuresthat the stand-by current is limited to 50µAmaximum in the off-state.

THE CONTROL CIRCUIT.Under voltage lock-out.Under-voltage protection occurs when thesupply voltage drops to a low levelspecified in the datasheet as VUSD. Theunder-voltage level set at this valueensures 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 of5µH( 5mt. of wire). Typically di/dt=0.5A/µsfor a normal load and 1A/µs for a shortcircuit. At turn on this generates anopposing voltage. If this opposing voltageis too large, the apparent supply voltagewill drop below the under-voltage lock-outlevel and the device will turn off. Usingthe specified conditions, the inducedvoltage will not be large enough to reducethe 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 headlampfilament turning on.

* Optional feature in the VNXXAN series

5/24

APPLICATION NOTE

Open load detection and stuck-on toVCC.Open load detection occurs when the loadbecomes disconnected. In the VN20Nfamily open load detection only occurs inthe on-state.

An extra feature for load disconnectiondetection is that open load detection duringthe off-state as well as in the on-state canbe provided. The circuit for the off-stateopen load detection requires an externalresistor between VCC and the output pin.

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

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

location of the sensing element on the chipin the power stage area, ensures thataccurate, very fast, temperature detectionis achieved. The range within whichover - tempera ture cu tou t occurs is140°C - 180°C with 160°C being a typicallevel.

Over-temperature protection acts toprotect the device from thermal damageand consequently also limits the averagecurrent when short circuits occur in theload.

Open load detection is possible in the off-state in the VN21 family and it conformsto the I .S.O. norms for automotiveapplications. If an open load condition isdetected the status flag goes low. Shouldan external supply be applied to the load(output pin) or the device is externally shortcircuited, the off-state open load detectioncan detect this “stuck-on” to VCC condition.

6/24

APPLICATION NOTE

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 toturn on the gate.

Turn-onAs previously explained, the High Side

Drivers are turned-on with a controlleddi/dt.

Turn-off: Normal and fast loaddemagnetizationWhen a High Side Driver turns off aninductance a reverse potential appearsacross the load. z

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

7/24

APPLICATION NOTE

The source of the power MOSFETbecomes more negative than the grounduntil it reaches the demagnetizationvoltage, Vdemag., of the specific device. Inthis condit ion the inductive load isdemagnetized and its stored energy isd i ss ipa ted in the power MOSFETaccording to the equation shown below:

VN20N VN21

In the basic High Side Driver family thetypical 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 typicalVdemag. = 18V.

In this condition the stored energy isremoved rapidly and the power dissipationin the power MOSFET is reduced - seeequation. Figure 7a/b compares thewaveforms of the normal and fastdemagnetization techniques.

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

[Vcc +Vdemag.]Pdemag.= 0.5 Lload [Iload]² ⋅ ------------------- ⋅ 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, thecurrent in the load rises linearly to amaximum. At turn-off the current decreaselinearly, 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 Driverw i t h n o s p e c i a l f e a t u r e f o r f a s tdemagnetization, the turn-off takes up to 5times longer than the VN21. Note that thestatus 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 thermalenvironment, is a function of the loadcurrent for a f ixed VCC, Vdemag. andswitching 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 loadcurrent for devices meet ing I .S.O.r e q u i r e m e n t s , a s s u m i n g a c h i ptemperature of 160°C at turn-off and asupply voltage of 13V. The values are fora single pulse with 85°C case temperature.Note that the devices are not protectedagainst overtemperature during turn-off.

APPLICATION NOTE

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

Additional Features of the High SideDriversHigh Side Drivers are designed for use invarious market segments, the preciserequirements of the drivers varying a littlewith the application. There are additionalf e a t u r e s t o a c c o m m o d a t e t h e s erequirements.

To reduce the on-state quiescent currentfor some applications, particularly industrialones, the open load detection circuit is notincluded. There will consequently also be alower power dissipation, an important pointwhen similar, multiple High Side Driversare mounted on one board. It can meansthe difference between using or not usinga heatsink.

9/24

CONDITIONS: VCC = 13V TC = 85°C

APPLICATION NOTE

The operating voltage range can vary e.g.5.5V to 26V for automotive applicationsand 7V to 36V for process control. Somedevices 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 filteredHigh Side Drivers is that the status outputfiltering circuit provides a continuous signalfor 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 5msdoes not affect the status output. Equally,any re-connection during a disconnectionof less than 5ms duration does not affectthe status output. No delay occours for thestatus to go low in case of overtemperatureconditions. From the falling edge of theinput signal the status output initially low infault condition (overtemperature or openload) will go back high with a delay tPOVL incase of overtemperature condition and adelay tPOL in case of open load. Thesefeatures fully comply with InternationalStandards Office, (I.S.O.), requirements forautomotive High Side Drivers.

ABNORMAL LOAD CONDITIONS:

Load short circuitsShould 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 andbegins 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 linearregion. When the silicon temperaturereaches about 160°C the over temperaturedetection operates and the switch is turnedoff. Passive cooling of the device occursuntil the reset temperature is reached andthe device turns back on again. The cycleis 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.

10/24

APPLICATION NOTE

Even in this configuration, the devicecontrols the di/dt. Figure 9 shows astart-up when there is a short circuited loaddriven by a VN05N. The initial peak currentis 30A for this 180mΩ device.

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

on-state, the power MOSFET gate isalready at a high voltage, about VCC+ 8V,so the gate is hard on. Hence the shortcircuit 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 inthe 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 upuntil 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.

11/24

APPLICATION NOTE

It is important to evaluate the average andRMS current during short circuit conditions.This is required in order to determine thetrack dimensions for printed circuit boardsand the correct value for any fuse used.In all practical situations there is no dangerto pcb tracks from these high peak currentfor track designed to handle the nominalload current.

Evaluating the Average currentIn steady state conditions the junctiontemperature osc i l la tes between T j(shutdown) and Tj (reset).

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

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, IRMS, generates heat inthe copper track on PCBs during shortcircuits.

T

I(RMS)2 = 1/T 0 I2(t)dt

I(RMS) = I(PK) x √Θ /T, where Θ/T is the duty cycle.

T

with I(AV) = 1/T 0 I(t)dt = I(PK) x Θ/T

I(RMS) = √ (I(PK) x I(AV))

Note that Iaverage does not depend on thepeak current I(PK) .

Example:VN21 with Tcase = 85°C has an averagecurrent, I(AV) = 3.85A, at Rthj-case = 1°C/W and VCC = 13VThe average current is independent of thepeak current.Generally, a current limiter does notdecrease the average current.

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

Θ

∫

12/23

∫

APPLICATION NOTE

Θ

The RMS current increases proportionallyto 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 deviceheating. I f you want to detect anoverload, i.e a damaged load, the chipmust be allowed to heat up so that thethermal sensor located on the chip isactivated. This leads to the followinggeneral 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 2Ω,- VN20N - RDS(on) at 25°C = 50mΩ- 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 150°C = 100mΩ(see datasheet) hence:

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

Rthj-a should be dimensioned for

Θthermal shutdown - ΘAmbient < PD x Rthj-a.

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

The effects of load disconnection.When a load becomes disconnected therecan 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 becomesdisconnected, the current changes at arate determined by the time taken for theload to disconnect. This controls di/dt .

APPLICATION NOTE

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

PROTECTION AGAINST GROUNDDISCONNECTIONThere are a number of distinct situationsthat can occur when one of the groundconnections is broken in circuits using theHigh Side Drivers.

The first case, shown in fig. 15a, is whenthe GND pin of the High Side Driver is

In this present case, there is virtually noinductance in the supply line. Hence noover-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 thatthe ove r -vo l tage may exceed thebreakdown voltage of the device. It is awise precaut ion where the supp ly

14/24

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

APPLICATION NOTE

disconnected while the µC and the loadare connected to ground. In this case inthe I.S.O. and industrial High Side Driversnothing 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) ⋅ ILOADusually very low. In these conditions thediagnostic is not functioning.

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

state at VCC. In the VN20N family a voltageof about 4V appears on the load andconseguently there is a power dissipation:PD = (VCC - 4) ⋅ ILOADIf PD is excessive with respect to theheatsink capability, destruction may occurssince 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 µC are disconnectedwhile the load is connected to ground. Inthis situation the signal GND rises up toVCC. In the I.S.O. and industrial High SideDrivers nothing happens up to VCC<18Vand the diagnostic output remains in high

Figure 15b : Possible ground disconnection occurring when a High Side Driver is connected toa µController (case 2)

15/24

APPLICATION NOTE

Another practical case is when an externalcomponent supplies current to the HighSide Driver GND pin which is disconnectedfrom 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 orbody 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 VCC the High Side

Driver is able to withstand before turningon with the control circuit in-operative.One solution to this problem is to insert aresistor and diode in between the deviceGND pin and the output pin. The seriesresistor, Rs, must be calculated so that thesum of the current, Is, of the High SideDriver chip connected to the GND nodeplus the current drawn by the externalelements, produces a voltage drop of lessthan 18V across Rs + Ds + Rload for 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 ofcontrolling a variety of inductive andresistive loads. The option to use aselection of extra features such as fastdemagnetization or status filtering makesthem equally suitable for general orspecialised use, typically in the automotiveenvironment.

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

16/24

APPLICATION NOTE

60V B(BR)DSS HIGH SIDE DRIVERS PRODUCT RANGE

VIPower

VN02NVN05NVN20NVN30N

VN03VN06VN21VN31

DEVICE RDS(on)@ 25°C(mohm)

4001805030

5001805030

VCCRange

(V)

7 - 267 - 267 - 267 - 26

5.5 - 265.5 - 265.5 - 265.5 - 26

Pentawatt/PowerSO-10TM

"""

PACKAGE

Pentawatt/PowerSO-10"""

EXTRAFEATURES

35050

7 - 367 - 36

Pentawatt/PowerSO-10"

VN02ANVN20AN

20010060

6 - 266 - 266 - 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

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ion

reve

rsed

;co

rrec

t co

nnec

tion

of

the

Hig

h S

ide

Driv

er d

evic

es.

the

su

pp

ly

volt

ag

e,V

D1

or D

2A

LLH

igh

Sid

e D

river

rev

erse

conn

ecte

d w

ith th

e ba

ttery

corr

ectly

con

nect

ed.

VC

C

Sch

ottk

y

drop

s to

VC

C.

SY

MP

TO

M

4S

uppl

y re

vers

al

5S

uppl

y re

vers

al -

cas

e 1

Sup

ply

reve

rsal

- c

ase

26

DE

VIC

E

APPLICATION NOTE

SC

HE

MA

TIC

CO

MP

ON

EN

T

RIN

PU

TD

rivi

ng

th

e

inp

ut

fro

m

avo

ltage

gre

ater

than

6V

R1

R2

Driv

ing

an in

duct

ive

load

, thi

ski

nd o

f di

scon

nect

ion

has

the

sam

e el

ectr

ical

effe

cts

as V

CC r

ever

sal.

CO

MM

EN

T

ALL

To

driv

e th

e in

put

from

a l

ine

volta

ge >

6V

ins

ert

a se

ries

resi

stor

to li

mit

the

inpu

t cur

rent

I IN m

ax <

10m

A

ALL

1) R

esis

tive

load

- n

o pr

oble

mof

dam

age.

VN

03V

N06

VN

21V

N31

VN

02A

NV

N20

AN

An

exte

rnal

com

pone

nt,R

eq,

supp

lies

curr

ent

to t

he H

igh

Sid

e D

river

GN

D p

in.

The

loca

l gro

und

is s

epar

ate

from

the

load

gro

und.

Th

e

de

vice

s a

re

inte

rna

llypr

otec

ted

(out

put

stag

e of

f) i

fth

e vo

ltage

on

the

GN

D p

in is

≤18

V w

ith r

efer

ence

to

the

real

grou

nd a

t Ø

V.

To

avoi

d th

eH

igh

Sid

e D

river

to

turn

-on

ifG

ND

is

over

18V

is

poss

ible

inse

rt R

s an

d D

s as

sho

wn

infig

ure.

Cho

ose

Rs

so t

hat

V1<

18V

SY

MP

TO

M

Inpu

t driv

ing.

Pin

dis

conn

ectio

n -

VC

C8

Pin

dis

conn

ectio

n -

Gro

und

97

20/24

2) In

duct

ive

load

- V

CC r

ever

sal

occ

urs

. If

cu

rre

nt

an

din

duct

ance

of

le

ads

are

to

oh

igh

th

e

de

vice

m

ay

be

dam

aged

but

th

e

safe

tym

argi

n is

wid

e -

up t

o 10

0mH

and

8A fo

r th

e V

N21

In t

his

case

, in

put

and

stat

uspi

ns a

re p

ulle

d to

a n

egat

ive

volta

ge s

o it

is r

ecom

men

ded

to in

sert

resi

stor

s in

ser

ies

with

thes

e pi

ns i

n or

der

to p

rote

ctth

eµC

.

NO

TE

SD

EV

ICE

APPLICATION NOTE

SC

HE

MA

TIC

CO

MP

ON

EN

T

ALL

Vol

tage

rang

e fo

r all H

igh

Sid

eD

river

s is

def

ined

bet

wee

nV

CCan

d V

SS

2 (V

Nxx

GN

D).

All

volta

ges

VIL

, V

IH,

VU

SD a

rere

fere

d to

VS

S2.

NO

TE

S

If V

SS

1 an

d V

SS

2 ar

e di

ffere

nt,

reca

lcul

ate

VIL

, V

IH,

VU

SD a

ndbe

war

e of

app

licat

ion

bugs

.(S

ee p

oint

s 11

/12/

13/1

4)

CO

MM

EN

T

ALL

D2

Usi

ng

p

ow

er

dio

de

to

with

stan

d re

vers

ed b

atte

ry.

Cas

e 1:

VS

S1

= V

SS

2 =

/= G

ND

with

VS

S1

> G

ND

Vol

tage

loss

es in

pow

er d

iode

.In

put

and

sta

tus

leve

ls a

ren

ot

eff

ect

ed

. U

nd

er-

volt

ag

esh

utdo

wn

leve

l in

crea

sed

bydi

ode

VF.

Off-

stat

e op

en lo

ad le

vel,

VR

EF,

incr

ease

d by

VF.

A g

ener

al r

ule

is:

leve

l sh

ift i

s(V

SS

2 -

GN

D).

D2

ALL

Usi

ng a

dio

de to

pro

tect

the

Hig

h

Sid

e

Dri

ver

ag

ain

stre

vers

ed b

atte

ry.

(See

poi

nt 6

abo

ve)

VS

S1

= V

SS

2 =

/= G

ND

with

VS

S1

> G

ND

Th

e

inp

ut

an

d

sta

tus

are

unaf

fect

ed.

VU

SD =

(V

SS

2 - G

ND

)+

VU

SD

o. O

ff-s

tate

ope

n lo

adle

vel,

VR

EF, i

s in

crea

sed

by (V

SS

2-

GN

D).

No

t su

ita

ble

if

th

eµC

on

tro

ller

use

s a

n

an

alo

gtr

ansd

ucer

ref

erre

d to

gro

und.

SY

MP

TO

M

Gro

und

pote

ntia

ldi

ffere

nces

10

Gro

und

pote

ntia

ldi

ffere

nces

- c

ase

111

Gro

und

pote

ntia

ldi

ffere

nces

- c

ase

212

DE

VIC

E

APPLICATION NOTE

21/24

22/24

SC

HE

MA

TIC

CO

MP

ON

EN

T

R1,

D2

CO

MM

EN

T

Usi

ng a

dio

de t

o pr

otec

t th

eH

igh

S

ide

D

rive

r a

ga

inst

reve

rsed

bat

tery

.

VS

S1

=/=

VS

S2.

VS

S2

> V

SS

1

VIL

and

VIH

shi

fted

by (

VS

S2

-V

SS

1).

R1

limits

any

neg

ativ

ecu

rren

t w

hen

the

µC

ontr

olle

rta

kes

I/O

to g

roun

d .O

n th

est

atus

pin

the

zero

cor

resp

onds

to t

he V

F o

f D

2, V

US

D a

nd V

OL

bein

g in

crea

sed

by (V

SS

2 - G

ND

).

R2,

D2

Usi

ng a

dio

de t

o pr

otec

t th

eµC

aga

inst

reve

rsed

bat

tery

.

VS

S1

=/=

VS

S2.

VS

S2

< V

SS

1

In f

ault

cond

ition

s th

e de

vice

pulls

the

sta

tus

pin

dow

n t

oV

SS

2 and

the

µCon

trol

ler s

ees

ane

gativ

e vo

ltage

- (

VS

S1 -

VS

S2)

.T

here

is a

risk

of l

atch

up

for t

heµC

ontr

olle

r CM

OS

out

put.

Add

R2

to

limit

the

curr

ent.

Und

ervo

ltage

and

off-

stat

e op

enlo

ad le

vels

are

not

shi

fted.

R1,

R2,

D2,

D7.

Rec

omm

ende

d sc

hem

e* c

omm

on g

roun

d fo

rµC

ontr

olle

r a

nd V

N d

evic

e*

Rev

erse

d ba

ttery

pro

tect

ion

-

Sch

ottk

y di

ode

* S

erie

s re

sist

or f

or in

put

and

s

tatu

s pi

ns*

Ove

r-vo

ltage

pro

tect

ion

- bi

-

dire

ctio

nal Z

ener

Gro

und

pote

ntia

ldi

ffere

nces

- c

ase

3

Gro

un

d

po

ten

tia

ldi

ffere

nces

- c

ase

4

13 14

Sum

mar

y

of

the

influ

ence

of

grou

nddi

ffere

nces

, pi

ndi

scon

nect

ions

and

over

vol

tage

pro

tect

ion.

15

ALL

ALLALL

NO

TE

SD

EV

ICE

SY

MP

TO

M

APPLICATION NOTE

23/24

SC

HE

MA

TIC

CO

MP

ON

EN

TC

OM

ME

NT

R1

In f

ull

bri

dg

e a

pp

lica

tion

sdu

ring

the

dem

agne

tizat

ion

phas

e V

LOA

D >

VC

C.

A c

urre

nt w

ill fl

ow o

ut o

f GN

Dpi

n, p

ossi

bly

dam

agin

g th

ebo

ndin

g.

ALL

D1

Hig

h

volt

ag

es

can

b

ege

nera

ted

if th

e ba

ttery

is

dis

con

ne

cte

d

wh

en

th

ege

nera

tor i

s ru

nnin

g in

a c

ar.

Da

ma

gin

g e

ffe

cts

can

be

ove

rco

me

b

y u

sin

g

acl

ampi

ng d

iode

with

at l

east

VB

R

>

26

V

as

2

x 1

2V

batte

ries

are

ofte

n us

ed t

oju

mp

st

art

ca

rs.

Th

is

for

over

volta

ge tr

ansi

ent h

ighe

rth

an s

peci

fied

in d

atas

heet

s.

Pro

tect

ion

agai

nst o

ver-

volta

ges

are

e

ffic

ien

t if

co

nn

ect

ed

betw

een

pin

3 (V

CC)

and

pin

1(g

roun

d).

ALL

Inse

rt

a

resi

sta

nce

, R

1(s

ugge

sted

val

ue 4

7Ω),

in

the

grou

nd p

in t

o lim

it th

e gr

ound

curr

ent a

nd a

void

dam

agin

g th

ebo

ndin

g.

DE

VIC

E

Lo

ad

d

um

p:

b

att

ery

disc

onne

ctio

n w

hils

t th

eal

tern

ator

is w

orki

ng

16

VLO

AD >

VC

C(B

ridge

circ

uit)

17

SY

MP

TO

MN

OT

ES

APPLICATION NOTE

APPLICATION NOTE

24/24

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequencesof use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license isgranted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication aresubject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics productsare not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.

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