ch7 protect high side drivers

Bridging Theory in PracticeTransferring Technical Knowledgeto Practical Applications

Protected High Side Drivers

Protected High Side DriversOvervoltage

ProtectionPower Stage

TemperatureSensor

CurrentControl

ChargePump

OvervoltageLogic

ESDProtection

OvervoltageProtection

Power OutputStage

Intended Audience:• Electrical engineers with a knowledge of simple electrical circuits• An understanding of MOSFETs and high side drivers is assumed

Topics Covered:• What is a PROFET?• What type of protection does a PROFET have?• What type of diagnostics does a PROFET have?• How does a PROFET impact system EMI?• How is a PROFET circuit implemented?• PROFET Selection Questions

Expected Time: • Approximately 90 Minutes

Protected High Side Drivers

• Introduction to PROFETs

• PROFET Protection Features

• PROFET Diagnostic Features

• EMI/EMC Considerations

• System Implementation

• Frequently Asked Questions

N-ChannelMOSFET

( Enhancement) (

MOSFET Metal Oxide Semiconductor Field Effect Transistor

GateSource Source

P-ChannelMOSFET

(Enhancement)

MOSFET Review

MOSFETRegions of Operation

• A positive (for N-Channel) or negative (for P-Channel) VGS produces a conducting channel between the Drain and Source

• The MOSFET is then able to operate in two regions:– 1) Linear region: The MOSFET behaves like a resistance.– 2) Saturation region: The MOSFET behaves like a current source.

VGS > 0V

N-ChannelMOSFET(NMOS)

VDS = VGS-VT

High Side Drive (HSD) Configuration

MOSFETSwitch

The switch is on the “HIGH”side of the load

To turn on the HSD, the MOSFETgate is pulled high

But, the maximum voltage at theMOSFET source is VG - VT

VS ~ 13V

The low value of VGS translatesinto a small ILOAD (saturation region)

VGS ~ 1V

High Side Drive (HSD)Configuration

MOSFETSwitch

The switch is on the “HIGH”side of the load

To turn on the HSD, the MOSFETgate is pulled high

The source voltage is now approximately Vsupply

VS ~ 14V

If the MOSFET gate is pulled toa higher voltage…

The high value of VGS translatesinto a large value of ILOAD

(linear region)

VGS ~ 14V

PROFETs = PROtected FETs

PROFET

MOSFETDiagnostics

Short CircuitProtection

IntegratedCharge Pump

OverVoltage

Protection

Current Limit

OverTemperature

Protection

ReverseBattery

Protection

Voltage Controlled PROFET Block DiagramVoltage Controlled

Current Controlled PROFET Block DiagramCurrent Controlled

Introduction to PROFETs

Rugged vs. ProtectedRugged

• MOSFETs• Achieved through

process & manufacturing technology

• Protection Not Built in

Protected • PROFETs• Achieved through design and

utilization of more advanced integrated circuit technologies

• Available CMOS, DMOS and Bipolar devices allow for the integration of ESD protection, active clamping, current limit, temperature sensing, etc.

• Protection Built in

PROtected FET (PROFET)Protection Features• Electrostatic Discharge (ESD) Protection• Overvoltage / Load Dump Protection• Overvoltage Shutdown Protection and Restart• Undervoltage Shutdown Protection and Restart• Reverse Battery Protection• Reversave™ Battery Protection• Inductive and Overvoltage Output Clamp Protection• Thermal Shutdown Protection• Current Limit Protection• Short Circuit Shutdown Protection• Inversave™ Inverse Current Protection• Loss of Ground Protection• Loss of Supply Voltage Protection

Block Diagram Including Protection Features

ESD Protection

Overvoltage Protection

Overvoltage Shutdown Protection and Restart

Undervoltage Shutdown Protection and Restart

Load Dump Protection

• The rated load dump voltage is a function of the generator impedance (RG) and the load resistance (RL)

• As RG and RL increase, less energy is dissipated in the PROFET, and the maximum allowable load dump voltage increases

4) The over temperature protection is not active during reverse current operation!

The PROFET will requires a 150 resistor in the GND connection to limit the reverse supply current.

Reverse Battery Protection

4) The temperature protection is not active during reverse current operation!

The reverse load current through the intrinsic drain- source diode has to be limited by the connected load. Power dissipation is higher compared to normal operating conditions due to the voltage drop across the drain-source diode.

4) The temperature protection is not active during reverse current operation!

PROFETs with ReverSaveTM

protection overcome thisproblem…

ReverSave™ Reverse Battery Protection

In PROFETs with ReverSaveTM protection, the MOSFET is turned on by the voltage drop across the resistor Rbb.

With the MOSFET conductingthe reverse load current (instead of the intrinsic diode), the power dissipation is greatly reduced under reverse batteryconditions.

Inductive and Overvoltage Output Clamp Protection

Thermal Shutdown Protection

A B C D E

InputVoltage

LoadCurrent

JunctionTemperature

Current Limit Protection

IL(SCr)

IL(SCp)

Short CircuitShutdown Protection

VON(SC)

Short CircuitShutdown Protection

Inversave™ Inverse Current Protection

Devices with Inversave™ can be operatedin inverse current mode.

When the device is off, only the intrinsic diode conducts with high power dissipation.

When device on, MOSFET turns on forlower power dissipation.

Loss of Ground Protection• With Loss of Ground Protection, Vbb, VIN, and VST are still

referenced to ground through the output• This ensures the device will be safely shut off if the ground pin

is opened

Loss of Supply Voltage Protection• All PROFETs are protected against a loss of supply voltage for

non-inductive loads• Most PROFETs are also protected against a loss of supply

voltage for inductive loads by handling the recirculation current through the GND pin

VOUT goes negative

PROFET Diagnostic Feedback Digital vs. Analog

ISTATUS

STATUS

Digital Diagnostic Feedback• The type of fault is determined by a diagnostic truth table

Normal Operation

Short Circuit to GND

Short Circuit to Vbb

Overcurrent

Overtemperature

Open Load

Output

Status

PROFET

StatusOutput

Analog Diagnostic Feedback• The type of fault is determined by a diagnostic truth

table AND a sense ratio parameter14V

PROFET

OutputRIS

Normal

Operation

Overcurrent

Short Circuit

to Ground

Overtemperature

Short Circuit

to Vbb

Open Load

Current

Output

Voltage

Current

IIS(LL)

nominal

IIS(LL)

IIS,FAULT

IIS(LL)

IIS,FAULT

IIS(LL)

IIS,FAULT

IIS(LL)

< nominal

IIS(LL)

IIS(LH)

Analog Load Current FeedbackVia IIS Current

• Under normal operation, IIS is proportional to the output current

• KILIS = IL / IIS ~ 10,000

• For example:IL = 25A

IIS ~ 2.5mA

IIS Current Sense Ratio• The accuracy of IIS improves with increasing output current

(IL / IIS)

IIS Current Sense Ratio

• The accuracy of IIS improves with increasing output current

Less Accurate

More Accurate

Status Signal Settling Time

• The Status signal is not valid during a settling time after turn-on, turn-off, or after change of load current

• This is true of PROFETs with analog or digital diagnostic feedback

Open Load DetectionThree Different PROFET strategies

• Open load detection via Sense pin on HiC (High Current) PROFETs and some PROFETs

• Open load detection while PROFET is turned on (for some PROFETS---mostly older types)

• Open load detection while PROFET is turned off (for most PROFETs---mainly newer types)

Open Load Detection – Via Sense Pin

Under an open load condition,the PROFET will maintain IIS below 1A (maximum).

CurrentSense

Open Load Detection – PROFET On

An open load is detected if the PROFET is on and the voltage across the MOSFET is

VON < RdsonIL(OL)

Open Load Detection - PROFET Off

Using an external resistor, an open load is identified if the PROFET is turned off and VOUT > 3.2V (typ.)

MOSFET High Side Drive

• Recall, the gate of the N-Channel MOSFET must be at a voltage higher than the transistor’s source to turn the MOSFET on:

• With VSUPPLY being the highest voltage in the system, where does VGATE come from?

MOSFETSwitch

VS ~ 14V

VGS ~ 12V

Charge Pump Gate Voltage• A charge pump is used to raise (pump) the gate

voltage to an acceptable level to turn on the MOSFET

Switch B

Switch A

VSUPPLY

Charge Pump Gate Voltage

• Initially, Switch A is closed, and CA is charged to VSUPPLY - VDA

Switch B

Switch A

VSUPPLY = 14V

• Next, Switch B is closed, and current flows from CA, through DB to charge CB

Switch B

Switch A

VSUPPLY = 14V

• But, CA acts like a battery in series with VSUPPLY

Switch B

Switch A

ReverseBiased

VSUPPLY = 14V

• Now, the High Side Drive MOSFET can be turned on

• The turning on and off of Switch A and Switch B, however, leads to a new problem….

MOSFET High Side Drive

MOSFETSwitch

VS ~ 14V

VGS ~ 12V

Charge Pump Electromagnetic Interference (EMI)

Frequency (MHz)

0.1 1 10 100 1000

1.0 10 1000.1

Charge pumpscan cause harmonic

emissions

Frequency (MHz)

1.0 10 1000.1

Newer, improved design reduces emissions

20 - 30 dB

PROFET’s Improved Charge Pump Reduces (EMI)

0.1 1 10 100 1000

Frequency [MHz]

BTS 736 L2ESG1

ESG2ESG3ESG4

ESG5 (DB)BMW

0.1 1 10 100 1000

Frequency [MHz]

BTS 736 L2

ESG1ESG2ESG3ESG4

ESG5 (DB)BMW

Filter solutions may be required for the charge pump

GND150

BTS736

Filtering - RC 150/4.7nF Filtering - C= 2µF

Continuous charge pump emissionContinuous charge pump emission

EMI/EMC Emissions due to PWM Operation• One source of EMI/EMC emissions is the internal charge pump as

shown on previous slides

• The other source of emissions can be PWM operation

• During PWM operation the slew rate and shape of the output voltage and current waveforms cause an increase in the emission spectra

• For slow switching applications (most Profets used at 100Hz) this results in an increase of the emission spectra below approximately 1Mhz.

Benefits of Edge Shaping• Edge shaping allows to reduce emission levels while maintaining a

slew rate which still allows for permissible power loss levels

Slew rate

control

Slew control only

Theoretical ideal

Edge shaping

Turn off edge shaping

Hi-Current Profet---EMC improvements• BTS650-Original Hi-current design with slew rate control only.• BTS6510-Same as BTS650 with longer switching times• BTS443P-Second generation with edge shaping for current turn off• BTS6143/44-Third generation with edge shaping for current turn on and offOperating point: Vs=13.5V, ILoad =5A, fs = 100Hz, resistive load

Emission Spectra:

0.1 1 10 100 1000

f / MHz

BTS650

BTS6510

BTS443

BTS6144P

Class 1 P

Class 2 P

Class 3 P

Class 4 P

Class 5 P

Device: BTS650 / BTS6510 / . BTS443 / BTS6144P0 / . BTS6144PLoad: 60W BulbO-Mode: PWM 100HzDetector: Peak

BTS 650 vs. BTS6510 vs. BTS 443 vs. BTS6144

Overvoltage Protection of Logic Functional Block

• RGND required to limit current through DAZ

• RST required to protect microcontroller input pin

• RIN may be required to protect microcontroller output pin

RINVAZ

Reverse Battery Protection• RGND required to limit current through logic zener diode

• RST required to protect microcontroller input pin

• RIN may be required to protect microcontroller output pin

• RL must limit current through power inverse diode

Reverse battery—Power Dissipation• Power dissipation during reverse battery can be higher than

normal operation due to conduction of load current through the FET body diode

• For example:– 3A load with 100mohm Fet in normal mode gives 0.9W– 3A load thru body diode in reverse battery gives 2.1W (3A*0.7V)

• The discrepancy between normal mode dissipation and reverse battery dissipation becomes worse as load current becomes higher

• Care must be take to control this dissipation to safe levels since over temperature protection is not active during reverse battery.

• This leads us to a feature where the MOSFET channel can be turned on during reverse battery operation---ReverSave

ReverSave™ Reverse Battery Protection Circuitry

• About 100mA of current must flow through the Rbb (from the IN or STATUS pins) to turn on the MOSFET in inverse mode

• Currents above 100mA in Rbb may create excessive power dissipation. Add RIN to limit

current below 100mA

IS Pin Overvoltage Protection• Overvoltage conditions greater than 67V (typ) can cause the IS pin to

exceed 5V - damaging a microcontroller input pin• The IS pin can be clamped by an external diode if necessary

PROFET Selection: Customer Questions

• How many channels?• What is the load current?• Is the load capacitive and what is the inrush current?• Is the load inductive and the inductance and/or energy during turn-off?• Will load be on/off or PWM? What is PWM frequency?• What is ambient temperature?• What type of package - surface mount or through-hole?• If surface mount, how much copper area for Vbb / tab connection?

• If through-hole, what type of heatsink will be provided for package?• What diagnostics are needed?• What application extremes will the device / system be subjected to

(reverse battery, load dump, overvoltage etc.)?

What Is the Load Current?• What is the maximum load current?• When does the maximum occur?• What is the typical load current?

• Alternative Question: What is the load resistance?

• Alternative Question: If the load is a lamp, what is it’s wattage?

• Recall, the load current is fundamental in determining an appropriate PROFET Rdson value

Is the Load Capacitive?What Is the In-rush Current?

• Recall, the in rush current for lamps and RC networks may be an order of magnitude higher than the steady state current

What Is Load Inductance or Energy During Turn-Off?

• FETs are rated for the max absorbable energy when turning off inductive loads

Will the Load Be On/Off or PWM? What is PWM frequency?

• PROFETs are often used in applications where the load is pulse width modulated – especially lighting applications

PWM Definitions• Frequency-(frequency domain) What is the rate of repetition of

a waveform?• Duty cycle-(Time domain) What is the amount of time spent on

with respect to the amount of time spent off?

T0 T1 T2 T3 T4

Period

Ton Toff

Frequency= 1/Period

Duty Cycle = Ton/(Ton+Toff)

Period = Ton + Toff

What Is the Ambient Temperature?• Minimum ambient temperatures is usually -40C

• Maximum ambient temperature ranges from 85C to 125C for most applications:

85C for most non-powertrain applications105C for some in-dashboard applications125C for most powertrain applications

What Type of Package?Surface Mount or Through-hole?• Many applications require all surface mount

components

• Surface mount components typically only have excess copper board space heatsinks

• Through-hole components can have large heatsinks for improved power dissipation

If Surface Mount - How Much Board Area Is Available for Heatsinks?

• Engineers must trade-off the cost and size of the heatsink vs. the Rdson (and hence, the cost) of the PROFET

Introduction to PROFETsOvervoltage

ProtectionPower Stage

TemperatureSensor

CurrentControl

ChargePump

OvervoltageLogic

ESDProtection

OvervoltageProtection

Power OutputStage

Thank You!www.btipnow.com

ch7 protect high side drivers

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