Bridging Theory in Practice

1
Bridging Theory in Practice

• Transferring Technical Knowledge
• to Practical Applications

2
Protected High Side Drivers
3
Protected High Side Drivers
4
Protected High Side Drivers

• 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

5
Protected High Side Drivers

• Introduction to PROFETs
• PROFET Protection Features
• PROFET Diagnostic Features
• EMI/EMC Considerations
• System Implementation
• Frequently Asked Questions

6
MOSFET Review
MOSFET ? Metal Oxide Semiconductor Field Effect
Transistor
D
G
VGS
S
VSG
S
G
P-Channel MOSFET (Enhancement)
D
7
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.

VDS VGS-VT
VGS gt 0V N-Channel MOSFET (NMOS)
IDS
VDS
8
High Side Drive (HSD) Configuration
The switch is on the HIGH side of the load
14V
MOSFET Switch
Load
9
High Side Drive (HSD)Configuration
The switch is on the HIGH side of the load
14V
MOSFET Switch
If the MOSFET gate is pulled to a higher voltage

Load
10
PROFETs PROtected FETs
MOSFET
PROFET
11
Voltage Controlled PROFET Block Diagram
Voltage Controlled
IN
12
Current Controlled
Current Controlled
Current Controlled PROFET Block Diagram
Current Controlled PROFET Block Diagram
IN
IIN
13
Introduction to PROFETs

• Introduction to PROFETs
• PROFET Protection Features
• PROFET Diagnostic Features
• EMI/EMC Considerations
• System Implementation
• Frequently Asked Questions

14
Rugged vs. Protected

• 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
• 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
• 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

• Rugged
• MOSFETs
• Achieved through process manufacturing
  technology
• Protection Not Built in

15
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

16
Block Diagram Including Protection Features
17
ESD Protection
18
Overvoltage Protection
VAZ
19
Overvoltage Shutdown Protection and Restart
20
Undervoltage Shutdown Protection and Restart
21
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

22
Reverse Battery Protection
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.
23
Reverse Battery Protection
4) The temperature protection is not active
during reverse current operation!
24
Reverse Battery Protection
4) The temperature protection is not active
during reverse current operation!
25
ReverSave Reverse Battery Protection
In PROFETs with ReverSaveTM protection, the
MOSFET is turned on by the voltage drop across
the resistor Rbb.
Rbb
With the MOSFET conducting the reverse load
current (instead of the intrinsic diode), the
power dissipation is greatly reduced under
reverse battery conditions.
26
Inductive and Overvoltage Output Clamp Protection
27
Thermal Shutdown Protection
Input Voltage
Load Current
Junction Temperature
A
B
C
D
E
F
28
Current Limit Protection
IL(SCp)
IL(SCr)
29
Short CircuitShutdown Protection
VON(SC)
30
Short CircuitShutdown Protection
31
Inversave Inverse Current Protection
Devices with Inversave can be operated in
inverse current mode. When the device is off,
only the intrinsic diode conducts with high
power dissipation. When device on, MOSFET turns
on for lower power dissipation.
32
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

33
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
I
34
Introduction to PROFETs

• Introduction to PROFETs
• PROFET Protection Features
• PROFET Diagnostic Features
• EMI/EMC Considerations
• System Implementation
• Frequently Asked Questions

35
PROFET Diagnostic Feedback Digital vs. Analog
STATUS
ISTATUS
GND
36
Digital Diagnostic Feedback

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

14V
Input
Output
Status
Normal Operation
L
L
L
Input
H
H
L
Short Circuit to GND
L
L
L
PROFET
H
L
H
Status
Short Circuit to
Vbb
L
H
H
H
H
L
Output
Overcurrent
L
L
L
H
H
L
Overtemperature
L
L
L
H
L
H
Load
Open Load
L
H
H
H
H
L
37
Analog Diagnostic Feedback

• The type of fault is determined by a diagnostic
  truth table AND a sense ratio parameter

Normal Operation Overcurrent Short Circuit to
Ground Overtemperature Short Circuit to Vbb Open
Load
Input Current L H L H L H L H L H L H
Output Voltage L H L H L L L L H H Z H
Current IIS IIS(LL) nominal IIS(LL) IIS,FAULT IIS(
LL) IIS,FAULT IIS(LL) IIS,FAULT IIS(LL) lt
nominal IIS(LL) IIS(LH)
14V
Input
PROFET
IIS
Output
RIS
Load
38
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

39
IIS Current Sense Ratio

• The accuracy of IIS improves with increasing
  output current

KILIS (IL / IIS)
40
IIS Current Sense Ratio

• The accuracy of IIS improves with increasing
  output current

More Accurate
Less Accurate
41
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

42
Open Load Detection

• Three 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)

43
Open Load Detection Via Sense Pin
Under an open load condition, the PROFET will
maintain IIS below 1?A (maximum).
Current Sense
44
Open Load Detection PROFET On
An open load is detected if the PROFET is on and
the voltage across the MOSFET is VON lt
RdsonIL(OL)
45
Open Load Detection - PROFET Off
Using an external resistor, an open load is
identified if the PROFET is turned off and VOUT gt
3.2V (typ.)
46
Introduction to PROFETs

• Introduction to PROFETs
• PROFET Protection Features
• PROFET Diagnostic Features
• EMI/EMC Considerations
• System Implementation
• Frequently Asked Questions

47
MOSFET High Side Drive

• Recall, the gate of the N-Channel MOSFET must be
  at a voltage higher than the transistors source
  to turn the MOSFET on
• With VSUPPLY being the highest voltage in the
  system, where does VGATE come from?

48
Charge Pump Gate Voltage

• A charge pump is used to raise (pump) the gate
  voltage to an acceptable level to turn on the
  MOSFET

VSUPPLY
DA
DB
VOUT
Switch B
CB
CA
Switch A
49
Charge Pump Gate Voltage

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

VSUPPLY 14V
DA
DB
VOUT
Switch B
CB
CA
Switch A
13V
50
Charge Pump Gate Voltage

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

VSUPPLY 14V
DA
DB
VOUT
Switch B
CB
CA
Switch A
13V
51
Charge Pump Gate Voltage

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

26V
VSUPPLY 14V
Reverse Biased
27V
DA
DB
VOUT
Switch B
CB
CA
Switch A
13V
52
MOSFET High Side Drive

• 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.

53
Charge Pump Electromagnetic Interference (EMI)
120
Charge pumps can cause harmonic emissions
100
80
dB?V
60
40
20
0
1.0
10
100
0.1
Frequency (MHz)
54
PROFETs Improved Charge Pump Reduces (EMI)
120
Newer, improved design reduces emissions 20 - 30
dB
100
80
dB?V
60
40
20
0
1.0
10
100
0.1
Frequency (MHz)
55
Filter solutions may be required for the charge
pump
Filtering - RC 150?/4.7nF
Filtering - C 2µF
Vbb
Vbb
OUT
BTS 736
OUT
BTS 736
IN
IN
CEMI
load
CEMI
GND 150?
load
GND
GND
Continuous charge pump emission
Continuous charge pump emission
56
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.

57
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 control only
Theoretical ideal
Turn off edge shaping
58
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 off

59
Introduction to PROFETs

• Introduction to PROFETs
• PROFET Protection Features
• PROFET Diagnostic Features
• EMI/EMC Considerations
• System Implementation
• Frequently Asked Questions

60
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

VAZ
RIN
RST
RGND
61
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

RIN
RST
RL
RGND
62
Reverse batteryPower 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 (3A0.7V)
• 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

63
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

64
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

65
Introduction to PROFETs

• Introduction to PROFETs
• PROFET Protection Features
• PROFET Diagnostic Features
• EMI/EMC Considerations
• System Implementation
• Frequently Asked Questions

66
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.)?

67
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 its wattage?
• Recall, the load current is fundamental in
  determining an appropriate PROFET Rdson value

68
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

69
What Is Load Inductance or Energy During Turn-Off?

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

70
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

71
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?

72
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 applications
• 105C for some in-dashboard applications
• 125C for most powertrain applications

73
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

74
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

75
Introduction to PROFETs

• Introduction to PROFETs
• PROFET Protection Features
• PROFET Diagnostic Features
• EMI/EMC Considerations
• System Implementation
• Frequently Asked Questions

76
Introduction to PROFETs
77
Thank You!

• www.btipnow.com