Introduction to automotive linear voltage regulators

What the Designer Should Know
Introduction to Automotive Linear Voltage Regulators
Issue 2014
www.infineon.com/voltage-regulator
Product Family Portfolio
New easy to use Selection Tool
www.infineon.com/vreg-finder
All products are Automotive qualified
and RoHS compliant
2
Content
Portfolio, Key Features, Key Benefits
4
Infineon’s Automotive Linear Voltage Regulators
6
Why do we need linear voltage regulators?
7
How does a linear voltage regulator work?
7
Different types of pass element
7
Adjustable output voltage
8
Embedded Protection
9
Thermal shutdown
9
Overvoltage
9
Current limitation
10
Safe operating area
10
Reverse polarity
10
Feature Description
13
Reset
13
Watchdog
15
Enable
19
Early warning
20
Application Details
21
Thermal considerations
21
Choice of output capacitance
23
Design of input protection
24
Drop-out voltage and tracking area
25
Load transients
26
Overshoot at start-up
27
PCB layout
28
Application Schematic
29
Packages
30
Glossary
31
3
Linear Voltage Regulators
Linear Voltage Regulator
Multiple output regulators
Quiescent current < 180µA
Yes
TLE4470
TLE4471
TLE4473
TLE4476
TLE7469
No
Enable
Enable
Yes
No
No
Yes
Reset
Reset
Yes
No
No
TLE7273-22)
TLE7278-2
Yes
TLE42994GM/E
TLE4699
TLE7279-2
Reset
Yes
TLE7272-2
Yes
TLE42364
TLE42344
TLE4284
TLE42901)
Yes
Watchdog
No
TLE4268
TLE4278
Early warning
No
No
Watchdog
No
TLE4678
TLE4678-23)
Early warning
Yes
No
Watchdog
Watchdog
Yes
Reset
No
TLE42644
TLE42744
TLE4294
TLE7274-2
TLF805113)
TLE42664
TLE42764/76-2
TLE4286
TLE4296/-2
TLE7276-2
Yes
Yes
TLE4263/-2
TLE4271-2
TLE42913)
Early warning
Yes
No
Yes
No
TLE42994G
TLE42754
TLE4285
TLE42951)
TLE4675
TLE7270-2
TLE42694
TLE42794
TLF49493)
TLE4270-2
No
TLE4262
TLE4267
TLE4287
1) Power good
2) Window watchdog
3) New devices
Selection tree
Key features
„„ Standard features
–– Wide operation range up to 45V
–– Low dropout voltage
–– Wide temperature range: -40°C up to +150°C
„„ Standard protections
–– Short-circuit protection
–– Reverse polarity protection as option
–– Overload protection
–– Overtemperature protection
Enable function for main output
Low quiescent current consumption in standby
mode
Adjustable reset function
Power-on reset circuit sensing the standby
voltage
Standard and window watchdog
Early-warning comparator for sensing input
undervoltage
4
Linear Voltage Regulators
High Performance Linear Voltage Regulator
Infineon’s Future Linear Voltage Regulator Family
200mA
Output current
500mA
Enable
Enable
Yes
No
Reset
No
Reset
Yes
Yes
Reset
Reset
No
Yes
No
No
Yes
No
TLS820B0
TLS820C0
TLS820A0
TLS850A0
TLS850C0
TLS850B0
Yes
Watchdog
Watchdog
Yes
No
No
Yes
TLS820F0
TLS820D0
TLS850D0
TLS850F0
1) None contractual product proposal: for more information on product family contact sale relations
Selection tree
Key features
Key benefits
LV124
severe
cranking
Ultra Low
Drop Voltage
Suitable for very low
cranking (stop and start)
3.2V
Low Quiescent
Current
Save battery resources for
ECUs in ON-state
40µA
85°C
Excellent Line &
Load Transient
ISO2a
pulse
Design for harsh
automotive environment
5
Linear Voltage Regulators
Infineon’s Automotive Linear Voltage Regulators
Supply line
Stabilized voltage
Input
VIN
e. g. car battery /
battery supply
Power stage
Reference
Protection
Error
amplifer
Voltage regulator
6
Output
VOUT
Output
stabilization
capacitor CQ
Load, e. g.
microcontroller,
sensor
Linear Voltage Regulators
Why do we need linear voltage regulators?
In automotive ECUs, microcontrollers and other parts of the
system have to be supplied by a stable and reliable voltage
that is lower than the battery voltage (e.g. 3.3V or 5V) and
works over the entire temperature range (from -40°C to
150°C). Use of discrete solutions does not manage to fulfill
those conditions because of voltage dependency on loadcurrent (e.g. resistor divider) or on temperature (e.g. Zener
diode).
A linear voltage regulator converts a DC input voltage (e.g.
battery line) into a pre-defined lower DC output voltage
(e.g. 5V). In spite of input voltage variations, the output
voltage remains steady and stable, as long as the input
voltage is greater than the output voltage. Linear voltage
regulators are the most frequently used electronic power
supplies in automotive applications.
Pass element
Input
VI
Output
VQ
Reference
Protection
Error
amplifer
Voltage regulator
Linear voltage regulator block diagram
How does a linear voltage regulator work?
Every linear voltage regulator consists of an internal
reference voltage, an error amplifier, a feedback voltage
divider and a pass transistor. The output current is
delivered via the pass element controlled by the error
amplifier. The error amplifier compares the reference and
output feedback voltages.
If the output feedback voltage is lower than the reference,
the error amplifier allows more current to flow through the
pass transistor, hence increasing the output voltage.
On the contrary, if the feedback voltage is higher than the
reference voltage, the error amplifier allows less current
to flow through the pass transistor, hence decreasing the
output voltage.
Different types of pass element
NPN linear regulators
C
E
Conventional linear regulators use NPN
bipolar transistors as the pass element.
B
Usually the pass element is composed of
a PNP base current driver transistor and a
NPN transistor
single NPN power transistor, therefore the
drop voltage, i.e. the minimum voltage difference between
input and output, is equal to VSAT(PNP) + VBE(NPN), which
is about 1.2V. Functionalities and integrated protection are
limited and additional protection circuitries are required.
PNP linear regulators
C
E
With only a single PNP bipolar transistor as
the pass element, the drop voltage of PNP
B
regulators is about 0.5V. For this reason,
this type of regulator is called Low Drop Out PNP transistor
(LDO). This enables it to operate during a
drop in battery voltage (e.g. cranking). PNP regulators are
protected against reverse polarity faults.
NMOS linear regulators
D
S
NMOS pass transistors provide very low
drop-out voltage and minimal quiescent
G
current. A charge pump is necessary to
achieve low drop-out voltage, because the
NMOS
gate of the NMOS needs to be ~2V higher
than the voltage at source to drive the pass element open.
However, the change pump also introduces additional line
noise.
PMOS linear regulators
S
D
PMOS linear regulators provide very low
drop-out voltage and minimal quiescent
G
current. An internal charge pump is not
necessary for the PMOS pass element.
PMOS
The new control loop concept in the new
Infineon PMOS linear regulators allows a faster regulation
loop and better stability, requiring only a single 1µF output
capacitor for stable operation.
7
Linear Voltage Regulators
Adjustable output voltage
The output voltage of some linear voltage regulators can be
adjusted by an external resistor divider, connected to the
voltage adjust pin named as ADJ or VA.
Supply
I
Q
CI
LDO
VDD
R1
CQ
MCU
ADJ/VA
GND
R2
GND
For a certain output voltage, the value of the external
resistors can be easily calculated with the formula:
(
R1 + R2
R2
)
Where:
„„ R2 < 50kΩ to neglect the current flowing into
the ADJ/VA pin.
„„ Internal reference voltage Vref is device-dependent.
The Vref value of a specific device can be found in its
datasheet.
If an output voltage equal to the reference voltage is
needed, the output pin Q has to be directly connected to
the voltage adjust pin ADJ/VA.
8
According to the datasheet
„„ Internal reference voltage Vref : typically 2.5V,
„„ Output voltage VOUT adjustable between
2.5V and 20V,
Required output voltage: VOUT = 3.3V.
The following resistors could be selected:
„„ R1 = 12kΩ, R2 = 39kΩ
It must be taken into consideration that the accuracy of the
resistors R1 and R2 adds an additional error to the output
voltage tolerance.
Application diagram
VQ = Vref ×
Example:
Selection of the external resistors for TLE42764GV/DV
1 I
Input
CI
e. g.
Ignition
Q 5
CQ
TLE42764
2
EN
VA
GND
3
Application diagram TLE42764GV/DV
Output
R1
4
Voltage
adjust
R2
Embedded Protections
Embedded Protections
Thermal shutdown
Overvoltage
Infineon’s automotive linear regulators are designed to
withstand junction temperatures up to 150°C. Package
and heat sink selections need to ensure that the maximum
junction temperature is not exceeded in any operating
condition.
High voltage transients are generated by inductive loads
(e.g. motor windings or long wire harnesses). In order to
provide sufficient protection in an automotive environment,
e.g. the load dump voltage, Infineon uses transistor
structures withstanding a continuous supply voltage VI up
to 45V. Additionally, several ICs offer protection against load
dump pulses up to 65V (e.g. TLE4270, TLE4271-2).
To prevent IC damage in fault conditions (e.g. output
continuously short-circuited), a thermal shutdown has
been integrated. The circuitry switches off the power stage
for a junction temperature higher than 151°C, typically
175°C, unless otherwise specified in the datasheet. The
device re-starts automatically after cooling down with a
typical hysteresis of 15K (e.g. with a thermal shut-down at
175°C, re-start occurs at 160°C).
Temperature above 150°C is outside the maximum ratings
of the voltage regulators and reduces the IC lifetime
significantly.
Exceeding any of these values may damage the IC
independent of pulse length. Therefore, a suppressor
diode is suggested to provide protection from overvoltage.
Moreover, transients can be buffered with an input
capacitor that takes the entire energy or some of it,
attenuating the surge at the IC input pin I.
In order to protect the voltage regulator output against
short circuits to the battery, the maximum voltage allowed
at the output Q is much higher than the nominal output
voltage. Therefore, all trackers and some voltage regulators
tolerate an output voltage up to VQ = 45V, which protects
them against shorts to battery at the output.
Tj
Tj,sd
For details please refer to “Absolute Maximum Ratings”
table in datasheet.
Tj,sdh = 15K
VI
t
e.g. 40V
VQ
Load dump transient
(suppressed)
VQ,nom
t
Thermal shutdown and hysteresis
13.5V
t
VQ
VQ,nom
t
Load dump transient
9
Embedded Protections
Current limitation
Safe operating area
In case of short-circuiting the output to GND or under
excessive load conditions, the regulator is forced to deliver
a very high output current. To protect the application as
well as the regulator itself against damage, the IC limits the
output current. Values are specified in the datasheet.
In order to avoid excessive power dissipation which cannot
be handled by the package, the voltage regulator decreases
the maximum output current (short-circuit current) at input
voltages above a certain voltage, e.g. 22V. That means that
at very high input voltages, the regulator is not able to
deliver the full (specified) output current.
During start-up, the output capacitor is charged up with
the maximum output current. Hence, the time until
nominal output voltage is reached after turning on the IC or
applying an input voltage is calculated as
tSTARTUP = VQ × CQ/IQ,MAX.
300
IQ [mA]
Two types of protection could be implemented: constant or
fold-back current limitation. Infineon linear regulators use
constant current limitation in order to overcome “latch-up”
problems with the fold-back limiting method: If the load
draws a current anywhere along the fold-back curve after
the removal of the fault condition, the output will never
reestablish its original voltage.
250
Tj = 25°C
200
Tj = 125°C
150
100
50
0
0
10
20
30
Maximum output current vs. input voltage (typical graph of TLE4678)
5
VQ [V]
50
VI [V]
6
4
Possible operation
point after removal
of fault condition
3
Constant
current
limitation
2
Foldback current
limitation
1
0
40
0
100
200
300
400
500
Reverse polarity
The following reverse polarity situations might occur in the
automotive environment:
„„ Output voltage higher than input voltage
(e.g. VI = 0V, VQ = 5V.)
„„ Input open, positive output voltage applied (i.e. VI = VQ).
„„ Input voltage negative, output tied to GND.
IQ [mA]
Current limitation
Voltage
regulator
-II
I
Negative
input
voltage
-IQ
Q
ESD
structure
CQ
GND
-IGND
Reverse current in the voltage regulator
10
Load
e.g. MCU
Embedded Protections
NPN bipolar voltage regulators (TLE4x8x)
Linear voltage regulators with an NPN pass transistor offer
no reverse polarity protection. If the input voltage is lower
than the output voltage, an unlimited current will flow
through parasitic junctions. Hence a blocking diode at the
input is needed to withstand a steady state reverse battery
condition. This series diode adds an additional drop and
must be sized to hold off the system’s maximum negative
voltage as well as the regulator’s maximum output current.
The typical reverse currents of bipolar PNP regulators are
shown in the graphs below:
20
0
VI = VQ
IQ [mA]
In reverse polarity situations, current may flow into the
GND pin of the regulator as well as into the output pin Q.
Depending on the type of the pass transistor, different
protection should be applied:
-20
VI = 0V
-40
-60
-80
TLE4275
-100
-II
Input
-IQ
0
5
10
15
20
25
VQ [V]
Output
Series
diode
Typical reverse current (TLE4275)
Reference
0
-IGND
II [mA]
-5
GND
PNP bipolar voltage regulators and trackers
(TLE4xxx except TLE4x8x)
Regulators with PNP pass transistors allow negative supply
voltage. The reverse current is limited by the PNP transistor
in reverse polarity conditions. Therefore a reverse
protection diode at the input is not needed.
-20
-25
TLE4275
-30
-40
-32
-24
-16
-8
0
VI [V]
Typical reverse current (TLE4275)
-IQ
Input
VQ = 0V
-15
Current in reverse polarity (NPN bipolar regulator)
-II
-10
Output
The reverse voltage causes several small currents to flow
into the IC, hence increasing its junction temperature.
As thermal shutdown circuitry does not work in the
reverse polarity condition, designers have to consider the
temperature increase in their thermal design.
Reference
-IGND
GND
Current in reverse polarity (PNP bipolar regulator)
11
Embedded Protections
MOSFET voltage regulators (TLE7xxx and TLF80511)
Linear voltage regulators with a MOSFET (NMOS or
PMOS) transistor as the pass element offer no reverse
polarity protection. An unlimited reverse current would
flow through the MOSFET’s reverse diode. Therefore, a
series diode at the IC input is mandatory. During normal
operation, it will be forward biased, adding an additional
drop voltage to the system. Therefore, a Schottky diode
with a low forward voltage is recommended.
Input
-II
Regarding the Enable (Inhibit) pin, negative voltages must
not be applied. Nevertheless, to allow negative transients
to flow, a high-ohmic resistor can be added in series to
protect the input structure. The maximum negative current
must not exceed 0.5mA.
e.g. Ignition
Negative
transient
100kΩ
100pF
EN
IREV
> 1MΩ
-IQ
ESDstructure
Output
Series
diode
Charge
pump
Battery
47µF
Reference
Logic
100nF
I
Pulldown
Voltage
regulator
GND
-IGND
Negative transients at the inhibit pin of an NMOS regulator
GND
Current in reverse polarity (NMOS regulator)
Input
-II
-IQ
Output
Series
diode
Reference
-IGND
GND
Current in reverse polarity (PMOS regulator)
12
Feature Description
Feature Description
Reset
Supply
I
CQ
LDO
CI
VDD
Q
RRO,ext4)
RO
Reset
MCU
Output undervoltage reset
The output undervoltage reset operates by sensing the
output voltage VOUT and comparing it to an internal reset
threshold voltage VRT. If the output voltage drops below
the reset threshold, the reset output is active low as long
as the low output state exists. The reset output is typically
connected to a microcontroller’s reset pin as shown in the
application circuit.
DT/RM/WM2)
RADJ,1
D1)
CD
RADJ3)
VQ
Optional
GND
RADJ,2
GND
1) Only available for the voltage regulators with RESET function in
TLE42xx series, TLE44xx series, TLE46xx series and TLF4949.
2) Only available for the voltage regulators with RESET function in
TLE72xx series and TLE7469. The name of this pin can differ
from device to device.
3) Not available for TLE4267, TLE4270-2, TLE4271-2, TLE42754, TLE4287,
TLE4473, TLE4675 and TLE72xx series.
4) The external pull-up resistor is mandatory for TLE42754, TLE42794,
TLE4290, TLE4473, TLE4675, as well as TLE72xx-2GV33/GV26 and
TLE7469GV52/GV53, optional for all other voltage regulators with
RESET function.
Reset application circuit
TLE42694/-2
TLE4270-2
TLE42754
TLE4278
TLE42794
TLE4287
TLE4291
TLE42994
Devices with digital reset
TLE7270-2
TLE7272-2
TLE7273-2
TLE7278-2
TLE7279-2
TLE7469
TLE4290
TLE4295
Power good
TLE4285
t
VD
VDL
t
VRO
t
trr
Output undervoltage reset
Devices with analog reset
TLE4262
TLE4263/-2
TLE4267/-2
TLE4268
Reset headroom
VRT
TLE4471
TLE4473
TLE4675
TLE4678
TLE4699
TLF4949
Reset reaction time
Short negative voltage spikes should not trigger an output
undervoltage reset. The undervoltage reset should only
be generated when the output voltage is below the reset
threshold for longer than the predefined reset reaction
time trr.
VQ
VRT
t < trr
VD
t
VDL
VRO
t
t
Reset reaction time
13
Feature Description
Power-on reset delay
Most control modules have a microcontroller and an
accompanying clock oscillator. When the module is turned
on, the clock oscillator requires a period of typically 1 to
10ms to reach a stable frequency. If the microcontroller
begins operating before the oscillator is stable, the
microcontroller may not initialize correctly. The power-on
reset delay prevents a microcontroller from initializing
while the oscillator is still stabilizing.
In case a power-on reset delay time trd different from the
value specified at CD = 100nF is required, the corresponding
value of the delay capacitor can be calculated as follows:
CD =
VRT
t
VD
VDU
t
VRO
trd,100nF
CD
100nF
t
× trr,d,100nF + trr,int
Digital reset timing
For the Infineon TLE72xx series linear voltage regulators,
the power-on reset delay time trd is selectable between two
predefined values through the configuration at the reset
timing selection pin DT/RM/WM (see application circuit).
Example: TLE7279-2 reset timing
Parameter
trd
× 100nF
Correspondingly, the reset reaction time trr can be
calculated with the formula:
trr =
VQ
trd
Power-on
reset delay
time
Symbol
trd
Limit values
Unit
Conditions
19.2
ms
Fast reset timing
RM = low
38.4
ms
Slow reset timing
RM = high
Min.
Typ.
Max.
12.8
16
25.6
32
Power-on reset delay
How to adjust reset timing?
Analog reset timing
For the Infineon TLE4xxx series and TLF4949 linear voltage
regulators, the power-on reset delay time trd and the reset
reaction time trr are determined by the delay capacitor CD
connected to the D pin (see application circuit).
In datasheets, the reset timing is given for a certain
capacitor, e.g. 100nF.
Example: TLE4291 reset timing
14
Parameter
Symbol
Limit values
Unit
Conditions
Min.
Typ.
Max.
Power-on reset
delay time
td,PWR,ON
8
13.5
18
ms
Calculated value;
CD = 100nF
Internal reset
reaction time
trr,int
–
9.0
15
µs
CD = 0nF
Delay capacitor
discharge time
trr,d
–
1.9
3
µs
CD = 100nF
Total reset
reaction time
trr,total
–
11.0
18
µs
Calculated value;
trr,d,100nF + trr,int;
CD = 100nF
Power good/power fail
In some Infineon voltage regulators, the power good/power
fail function is implemented. This functionality is similar to
the reset function.
In TLE4290, output voltage is supervised through a power
good circuit. This function is the same as an analog reset,
including delay timing set by a delay capacitance as
described above for analog reset timing.
In TLE4285 and TLE4295, output undervoltage is alerted by
the power fail (PF) pin. As soon as VQ falls below its power
fail switching threshold, its output PF is set to LOW. There is
no delay pin available for connecting an external capacitor
to set a reaction or delay time.
In the voltage tracker TLE4254, the power good function
not only alerts the undervoltage, but also the overvoltage,
providing an added safety feature.
Feature Description
In some linear voltage regulators, RO output is internally
pulled up to the output voltage. An external pull-up resistor
to the output Q can be added, in case a lower-ohmic
RO signal is desired. As the maximum RO sink current is
limited, a minimum value of the external resistor RRO,ext is
specified in the datasheet and must be adhered to.
Example:
TLE4291 RO internal and external pull-up resistors
Parameter
Symbol
Limit values
Min.
Typ.
Max.
Unit
Conditions
Reset output
external pull-up
resistor to Q
RRO,ext
5.6
–
–
kΩ­­
1V ≤ VQ ≤ VRT,low;
VRO = 0.4V
Reset output
internal pull-up
resistor
RRO
20.0
30
40
kΩ
Internally
connected
to Q
Watchdog
Supply
I
LDO
CI
Example: TLE42754 RO external pull-up resistor
Parameter
Reset output
external pull-up
resistor to VQ
Symbol
RRO
Limit values
Min.
Typ.
Max.
5
–
–
Unit
Conditions
kΩ­­
1V ≤ VQ ≤ VRT;
VRO = 0.4V
VDD
CQ
WO
WI
MCU
RWO,ext
Reset
I/O
WM12)
WM22)
D1)
WADJ3)
GND
CD
GND
RWADJ
1) Only available for TLE4263-2, TLE4268, TLE4271-2, TLE4291, TLE4278,
TLE4678, TLE4471, TLE4473
2) Only available for TLE7273-2, TLE7278-2, TLE7469
3) Only available for TLE4278, TLE4678
Watchdog application circuit
Devices with standard watchdog
TLE4263/-2
TLE4268
In some other regulators, there is no internal pull-up
resistor at RO to the output voltage. For those regulators
an external pull-up resistor is required. The minimum value
of the required external pull-up resistor RRO is given in the
datasheet.
Q
Optional
Tips & tricks
Pull-up at reset output RO
The reset output RO is an open collector output requiring
a pull-up resistor to a positive voltage rail (e.g. output
voltage VQ).
TLE4278
TLE4291
TLE4471
TLE4473
TLE4678
TLE7278-2
Devices with window watchdog
TLE7273-2
TLE7469
Why do we need a watchdog?
The watchdog monitors the microcontroller to ensure it is
operating normally. The function of the watchdog timer is
to monitor the timing of the microcontroller and reset it
to a known state of operation in case of an obvious timing
error. For example, a microcontroller could get stuck in a
software loop and stop responding to other inputs. If too
much time elapses between triggers, the watchdog senses
that something is wrong and sends a reset signal to the
microcontroller.
VWI
VWO
Missing
trigger pulse
t
t
Standard watchdog
15
Feature Description
VWI
VWI,high
VWI,low
dVWI/dt
Outside spec
No positive
VWI edge
VD
tWI,tr
1/fWI
tWI,p
t
tWI,p
VDW,high
VDW,low
Reset condition
Charge/discharge curve of
CD timing defined by CD
tWD,low
t
tWD,low
VWO
VWO,low
t
Watchdog timing (analog implementation)
Watchdog timing – analog implementation1)
Positive edges at the watchdog input pin “WI” are expected
within the watchdog trigger timeframe tWI,tr, otherwise a
low signal at pin “WO” is generated and it remains low for
tWD,low. All watchdog timings are defined by charging and
discharging capacitor CD at pin “D”. Thus, the watchdog
timing can be programmed by selecting CD.
In the datasheet, reset timing is given for a certain
capacitor, e.g. 100nF.
Example: TLE4678 watchdog timing
Parameter
Symbol
Limit values
Unit
Conditions
Min.
Typ.
Max.
Watchdog
trigger time
tWI,tr,100nF
25
36
47
ms
Calculated value;
CD = 100nF
Watchdog
output low
time
tWD,low,100nF
13
18
23
ms
Calculated value;
CD = 100nF
VQ > VRT,low
Watchdog
period
tWD,p,100nF
38
54
70
ms
Calculated value;
tWI,tr,100nF + tWD,low,100nF
CD = 100nF
In case a watchdog trigger time period tWI,tr different
from the value specified at CD = 100nF is required, the
corresponding value of the delay capacitor value can be
derived as follows:
CD = 100nF ×
tWI,tr
tWI,tr,100nF
Watchdog output low time tWD,low and watchdog period
tWD,p can be derived using:
tWD,low = tWD,low,100nF ×
1) Applicable to TLE4263-2, TLE4268, TLE4271-2, TLE4291, TLE4278, TLE4678,
TLE4471, TLE4473
16
tWD,p = tWI,tr + tWD,low
CD
100nF
Feature Description
Watchdog timing – digital implementation 1)
WM1
L
L
H
H
WM2
L
H
L
H
Watchdog mode
Fast
Slow
Fast
Off
Reset mode
Fast
Slow
Slow
Slow
The watchdog uses an internal oscillator as its time base.
The watchdog time base can be adjusted using the pins
WM1 and WM2.
Reset
Trigger during
closed window
Symbol
Ignore window
time
tOW
Watchdog
period
tWD,p
Limit values
No trigger during
open window
Ignore
window
Always
Trigger
Example: TLE7273-2 watchdog timing
Parameter
Always
Unit
Conditions
Min.
Typ.
Max.
25.6
32
38.4
ms
Fast watchdog
timing
51.2
64
76.8
ms
Slow watchdog
timing
25.6
32
38.4
ms
Fast watchdog
timing
51.2
64
76.8
ms
Slow watchdog
timing
Window watchdog 2)
For safety-critical applications a more advanced watchdog
called window watchdog is provided for higher security of
the system. The window watchdog operates in a similar
manner to the standard watchdog except a trigger must
occur within a certain window or time slot. If a trigger
occurs outside of the window or does not occur at all within
the designated window, the window watchdog will reset
the microcontroller. When an unintentional trigger occurs,
the standard watchdog is not able to decipher if this trigger
is valid. The window requirement enables the window
watchdog to detect unintentional triggers.
Closed
window
Open
window
No trigger
Window watchdog
Load-dependent watchdog activation
If a microcontroller is set to sleep mode or to low power
mode, its current consumption is very low and it might
not be able to send any watchdog pulses to the voltage
regulator’s watchdog input “WI”. In order to avoid
unwanted wake-up signals due to missing edges at
pin “WI”, the watchdog function of some linear voltage
regulators can be activated dependent on the regulator’s
output current.
The load-dependent watchdog activation feature is
available on TLE4268, TLE4278, TLE4678, TLE7273-2 and
TLE7278-2.
On voltage regulators TLE4268, TLE7273-2 and TLE7278-2,
watchdog activation and deactivation thresholds are fixed.
On voltage regulators TLE4278 and TLE4678, the watchdog
can be permanently activated or deactivated, or enabled/
disabled by defining a current threshold through the
external resistor at the WADJ pin:
„„ An external resistor at WADJ to GND determines the
watchdog activation threshold.
„„ Connect WADJ directly to GND to permanently deactivate
the watchdog.
„„ Connect WADJ to the output Q via a 270kΩ resistor to
permanently activate the watchdog.
1) Applicable to TLE7273-2, TLE7278-2, TLE7469
2) The window watchdog is available for voltage regulators TLE7273-2 and TLE7469.
17
Feature Description
Vi/V
VQ/V
VRT
IQ/A
VRO/V
trd
trr
Normal operation
trd
trd
Wnd
Ingnore
window
WDI/V
Don’t care WDI
during IW
1. Long
OW
CW
OW
CW
1. Long
OW
OW
1. Correct
trigger
CW
(Wrong) Trigger
in CW
No trigger in OW
tWD,p
Watchdog timing (window watchdog)
Disadvantage of a standard watchdog
It is possible that the microcontroller could become
trapped in a routine of only emitting the pulses. The
standard watchdog is not capable of detecting this
potential program error and would interpret this signal as
valid. The solution in this case would be to use the window
watchdog.
VWI
VWO
Unwanted
trigger pulse
Missing
trigger pulse
Window watchdog
To further reduce the potential risk of program errors, a
more advanced watchdog called window watchdog has
been implemented. It offers higher system security. A
window watchdog monitors not only the minimum pulse
period, but also the maximum pulse period. A watchdog
pulse must occur within a certain window or time slot. If a
pulse occurs outside of the window or does not occur at all
within the designated window, the window watchdog will
reset the microcontroller.
VWI
t
Standard watchdog
VWO
Unwanted
trigger pulse
t
Window watchdog
t
t
Disadvantage of standard watchdog
18
Missing
trigger pulse
Advantage of window watchdog
Feature Description
Tips & tricks
Watchdog deactivation
In some applications, the microcontroller software is
stored in an external non-volatile memory and needs to
be downloaded to the microcontroller after every start-up.
During this download, the microcontroller is not able to
send any watchdog pulses. To skip unwanted watchdog
alerts due to missing WI-input edges, the watchdog
function should be deactivated.
The watchdog function can be easily deactivated by
connecting WADJ directly to GND for those regulators with
an adjustable watchdog activation threshold (TLE4278 and
TLE4678).
Enable
Supply
I
Output
Q
CI
CQ
LDO
e. g. Ignition
EN/INH
GND
Enable application circuit
Devices with enable
For other linear regulators, the watchdog function could
be deactivated by connecting the D pin to the output Q via
a pull-up resistor to compensate the discharge current of
the watchdog. The pull-up resistor can be determined by
referring to the delay capacitor discharge current specified
in the datasheet.
Example: watchdog deactivation for TLE4263-2
Parameter
Discharge current
Symbol
ID,wd
Limit values
Min.
Typ.
Max.
4.40
6.25
9.40
Unit
Conditions
µA
VD = 1.0V
Formula to apply:
RPU,D ≤ (VQ – VD)/ID,wd,max = (5.0V – 1.0V)/9.40µA = 425kΩ
Taking some headroom for tolerances, a 390kΩ pull-up
resistor could be recommended for deactivating the
watchdog function on the TLE4263-2.
TLE42364
TLE4262
TLE4263/-2
TLE4266-2
TLE42664
TLE4267/-2
TLE4276-2
TLE42764
TLE4286
TLE4287
TLE4291
TLE4296/-2
TLE42994
TLE4471
TLE4473
TLE4476
TLE4699
TLE7272-2
TLE7273-2
TLE7276-2
TLE7278-2
TLE7279-2
TLE7469
Why do we need enable?
Many linear voltage regulators can be turned off with an
enable control input. In some automotive and batteryrun applications, it is necessary to significantly reduce
the quiescent current when the module is off. This can be
accomplished by turning off the linear voltage regulator
with low-logic signal (0V) applied to the EN pin. To turn on
the regulator again, a high-logic signal (e.g. 5V) is applied to
the EN pin.
This function is also called inhibit and the corresponding
pin is called INH in some older voltage regulators.
If the enable/inhibit function is not used, the EN or INH pin
must be connected to the input I.
Example: TLE42994 current consumption
VI = 13.5V; Tj = -40°C < Tj < 150°C
Parameter
Symbol
Limit values
Min.
Typ.
Max.
Unit
Conditions
Current consumption;
Iq = II - IQ
Iq
–
65
1051)
µA
Enable HIGH1);
IQ ≤ 1mA1);
Tj < 85°C
Current consumption;
Iq = II - IQ
Iq
–
–
12)
µA
VEN = 0V 2);
Tj = 25°C
1) Though no output current is flowing, the regulator is still supplying the nominal
output voltage and consumes some current.
2) The output voltage is switched off by EN/INH, the regulator consumes only very
low stand-by current.
19
Feature Description
Tips & tricks
TLE4267 inhibit/hold function
In microcontroller supply systems, enable/inhibit might
be controlled by the ignition key. Microcontrollers must
be able to store data in case the ignition key is turned
off. The additional HOLD pin of the TLE4267 allows
microcontrollers to control the turn-off sequence. The
voltage regulator remains on after inhibit is turned off as
long as the microcontroller keeps the HOLD pin active low.
The microcontroller can then release the HOLD signal when
it is ready to be switched off, and then the voltage regulator
will be turned off.
VBAT
I
Q
VDD
TLE4267
Ignition
INH
MCU
HOLD
I/O
its start-up state when it powers up again and the reset is
released.
The early warning function is generally an integrated and
independent comparator with a status output, which can
compare any external voltage with the internal reference
voltage. Besides the input voltage, this function can be
used to sense any voltage rail on the board, sending a high/
low status signal to a logic-IC or a microcontroller. For this
reason, this function is also called the sense function.
Early warning function
The early warning function monitors the input voltage
by comparing a divided sample of the input voltage to a
known reference voltage. When the voltage at the sense
input (SI) VSI drops below the sense low threshold VSI,low an
active low warning signal is generated at the sense output
(SO) pin.
Sense input
voltage
VSI,high
TLE4267 inhibit/hold function
VSI,low
Early warning
High
Supply
I
CI
Q
LDO
RSI1
SI
RSI2
VDD
CQ
MCU
RSO1)
SO
t
GND
GND
Early warning function
Devices with early warning
TLE4699
TLE7469
The desired threshold voltage for the input voltage is
adjustable through the external voltage divider:
VI,TH = VSI ×
Early warning application circuit
TLE7279-2
TLF4949
Why do we need early warning?
The purpose of the early warning function is to alert the
micro­controller that the supply voltage is dropping and a
reset signal is imminent. This allows the microcontroller
to perform any “house cleaning” chores like saving RAM
values into EEPROM memory so it can resume operation at
20
Low
I/O
1) The external pull-up resistor is mandatory for TLE42794,
TLE72xx-2GV33/GV26 and TLE7469GV52/GV53,
optional for all other voltage regulators with Early Warning function.
TLE42694
TLE42994
t
Sense output
(
RSI1 + RSI2
RSI2
)
VI,TH: desired threshold triggering the early warning.
VSI: given in the datasheet by VSI,low and VSI,high.
Example: TLE42694 early warning thresholds
Parameter
Symbol
Limit values
Min.
Typ.
Max.
Unit
Sense threshold high
VSI,high
1.24
1.31
1.38
V
Sense threshold low
VSI,low
1.16
1.22
1.28
V
Sense switching hysteresis
VSI,hy
20
90
160
mV
Application Details
Application Details
Thermal considerations
The maximum junction temperature allowed for most
Infineon automotive linear voltage regulators is 150°C.
The thermal shutdown protection can prevent the device
from direct damage caused by an excessively high junction
temperature. Moreover, exceeding the specified maximum
junction temperature reduces the lifetime of the device.
A proper design must ensure that the linear regulator is
always working beneath the allowed maximum junction
temperature as specified in the datasheet of the device.
The maximum an acceptable thermal resistance RthJA can
then be calculated:
RthJA,max = (Tj,max – Ta)/PD
Based on the above calculation the proper PCB type and
the necessary heat sink area can be selected with reference
to the thermal resistance table in the regulator’s datasheet.
Below is an example of the thermal consideration for an
application with TLE42754G.
Example: TLE42754G thermal resistance
Thermal resistance
Thermal resistance is the temperature difference across
a structure in the presence of a unit of power dissipation.
It reflects to the capacity of the package to conduct heat
outside the device. It is the key parameter to be considered
in the thermal design. The most useful thermal resistance
for thermal calculation is the junction-to-ambient thermal
resistance RthJA. In most datasheets, junction-to-ambient
thermal resistance RthJA is specified in accordance with
JEDEC JESD51 standards defining PCB types and heat sink
area.
1.5mm
70µm Cu
Parameter
Symbol
Limit values
Unit
Conditions
–
k/W
–
Min.
Typ.
Max.
3.7
Junction to
case1)
RthJC
–
Junction to
ambient
RthJA
–
22.0
–
k/W
2)
–
70.0
–
k/W
Footprint only 3)
–
42.0
–
k/W
300mm2 heatsink
area on PCB 3)
–
33.0
–
k/W
600mm2 heatsink
area on PCB 3)
1) Not subject to production test, specified by design.
2) Specified RthJA value is according to Jedec JESD51-2, -5, -7 at natural convection
on FR4 2s2p board; The product (chip + package) was simulated on a
76.2 x 114.3 x 1.5 mm3 board with 2 inner copper layers (2 x 70µm Cu, 2 x 35µm Cu).
Where applicable a thermal via array under the exposed pad contacted the first
inner copper layer.
3) Specified RthJA value is according to JEDEC JESD 51-3 at natural convection on
FR4 1s0p board; The product (chip + package) was simulated on a
76.2 x 114.3 x 1.5 mm3 board with 1 copper layer (1 x 70µm Cu).
70µm Cu
1.5mm
Cross section JEDEC 1s0p board
70µm Cu
35µm Cu
35µm Cu
70µm Cu
Cross section JEDEC 2s2p board
Thermal calculation
Knowing the input voltage, the output voltage and the load
profile of the application, the total power dissipation can
be calculated:
PD = (VIN – VOUT) × IOUT + VIN × Iq
Example: Thermal calculation for TLE42754G
Application conditions:
VIN = 13.5V
VOUT = 5V
IOUT = 200mA
Ta = 85°C
Determination of RthJA:
PD
= (VIN – VOUT) × IOUT + VIN × Iq
= (13.5V – 5V) × 250mA + 13.5V × 10mA
= 2.125W + 0.135W = 2.26W
RthJA,max = (Tj,max – Ta)/PD = (150°C – 85°C)/2.26W = 28.76K/W
As a result, the PCB design must ensure a thermal
resistance RthJA lower than 28.76K/W. Referring to the
thermal resistance table of the TLE42754G, only a FR4 2s2p
board could be used.
21
Application Details
Transient thermal resistance
Thermal resistance constant RthJA reflects the steady-state
condition of the power dissipation. In other words, the
amount of heat generated in the junction of the device
equals the heat conducted away. In some applications, the
worst case conditions for power dissipation occur during
the transient state. The duration in transient could be far
shorter than steady-state.
Thermal impedance curves characterize delta temperature
rise (between junction and ambient) versus power
dissipation as a function of time. In this case, the junction
temperature will be a function of time:
Tj(t) = ZthJA(t) × PD(t) + Ta
45
40
Zth-JA/C [K/W]
35
30
Zth-JA 1s0p with
600m2 cooling area
Zth-JA 1s0p with
300m2 cooling area
Zth-JA 2s2p
Zth-JC,bottom
Tips & tricks
Calculation example in transient based on TLE42754G. The
following load current profile is applied.
IQ
IQ1
IQ2
IQ,steady
t1
Application conditions:
VIN = 13.5V
VOUT = 5V
Ta = 85°C
PCB: JEDEC 2s2p
t2
t
Load current:
IQ1 = 400mA
IQ2 = 250mA
IQ,steady = 100mA
t1 = 10ms
t2 = 10s
25
20
15
10
5
0
10-5 10-4 10-3 10-2 10-1 100 101 102 103 104
t [s]
Thermal impedance curve of TLE42754 in PG-TO263 package
Determination of junction temperature Tj:
P1
= (VI – VQ) × IQ1 + VI × Iq1
= (13.5V – 5V) × 400mA + 13.5V × 25mA
= 3.74W
Tj,t1
= Ta + P1 × RthJA,10ms
= 85°C + 3.5K/W × 3.74W = 85°C + 13.1°C
= 98.1°C < 150°C
P2
= (VI – VQ) × IQ2 + VI × Iq2
= (13.5V – 5V) × 250mA + 13.5V × 10mA
= 2.26W
Tj,t2
= Ta + P2 × RthJA,10s
= 85°C + 10.5K/W × 2.26W
= 108.7°C < 150°C
Psteady = (VI – VQ) × IQ,steady + VI × Iq,steady
= (13.5V – 5V) × 100mA + 13.5V × 1.5mA
= 0.87W
Tj,steady = Ta + Psteady × RthJA
= 85°C + 22K/W × 0.87W
= 104.1°C < 150°C
The calculation result shows that the junction temperature
of TLE42754G never exceeds the maximum threshold of
150°C. This is a valid thermal design.
22
Application Details
Choice of output capacitance
An output capacitor is mandatory for the stability of
linear voltage regulators. A linear voltage regulator can
be described as a simple control system and the output
capacitor is a part of the control system. Like all control
systems, the linear voltage regulator has regions of
instability. These regions depend to a great extent on two
parameters of the system: the capacitance value of the
output capacitor and its equivalent serial resistance ESR.
VSupply
I
Q
VDD
Linear voltage
regulator
CQ
There are some older linear voltage regulators (see the list
below) which require a small amount of ESR at the output
capacitor for stability. Those regulators were designed
some time ago when tantalum capacitors were widely
used. So, it is recommended to connect an additional series
resistor to the capacitor if a ceramic capacitor is used.
Load
ESR
10
9
GND
8
ESR [Ω]
GND
Most Infineon linear voltage regulators are designed to be
stable with extremely low ESR capacitors. According to the
automotive requirements, ceramic capacitors with X5R or
X7R dielectrics are recommended.
Application diagram
7
6
5
4
The requirement for the output capacitor is specified in the
datasheet of each linear voltage regulator.
Stable region
3
2
Example: TLE42754 output capacitor requirements
Parameter
Symbol
Output
capacitor‘s
requirements
for stability
Limit values
Unit
Conditions
–
µF
The minimum output
capacitance requirement is
applicable for a worst case
capacitance tolerance of 30%
3
Ω
Relevant ESR value at f = 10kHz
Min.
Max.
CQ
22
ESR (CQ)
–
1
0
0.2
Typically an ESR versus output current plot can be found
in the datasheet of Infineon voltage regulators showing the
stability region.
100
101
IQ [mA]
102
500
Stability graph with minimum ESR requirement (TLE4271-2)
Devices requiring small amount of ESR at CQ
TLE42344
TLE42364
TLE4263/-2
TLE4268
TLE4270-2
TLE4271-2
TLE4278
TLE4285
TLE4290
TLE4294
TLE4295
TLE4296
TLE4471
TLF4476
103
ESR (CQ) [Ω]
10
It is very important to comply with the requirements of
the output capacitor as specified in the datasheet during
selection. If the specified requirements are not fulfilled, the
voltage regulator can be unstable and the output voltage
can oscillate.
CQ = 22µF
Tj = -40 … 150°C
VI = 6 … 28V
2
Unstable
region
101
100
Stable
region
10-1
10-2
0
100
200
300
400
500
IQ [mA]
Stability graph without minimum ESR requirement (TLE42754)
23
Application Details
Tek
Stopped
1794 Acqs
26 Jun 13 10:19:36
Design of input protection
4 Reverse polarity diode
(recommended)
1 Input capacitor
(recommended)
I
Line
Battery
2
< 40V
10µF…
470µF
100nF…
470nF
VQ
Q
Linear
voltage
regulator
GND
VDD
CQ
Load
GND
2 Input buffer
3 Overvoltage
suppressor
(recommended)
diode (optional)
Ch2 100mV
M 400µs 500KS/s 2.0µs/pt
A Ch1 / 1.0V
Stable output with CQ and ESR (CQ) according to the datasheet
Tek
Stopped
65 Acqs
26 Jun 13 10:22:15
Design of input protections
The figure above shows the typical input circuitry for
a linear voltage regulator. Though input filtering is not
mandatory for the stability of a linear regulator, some
external devices and filtering circuits are recommended
in order to protect the linear voltage regulator against
external disturbances and damage.
1 A ceramic capacitor at the input in the range of 100nF
to 470nF is recommended to filter out the high frequency
disturbances imposed by the line, e.g. ISO pulses 3a/b. This
capacitor must be placed very close to the input pin of the
linear voltage regulator on the PCB.
2
VQ
An aluminum electrolytic capacitor in the range of 10µF
to 470µF is recommended as an input buffer to smooth out
high energy pulses, such as ISO pulse 2a. This capacitor
should be placed close to the input pin of the linear voltage
regulator on the PCB.
2
Ch2 100mV
M 4.0µs 50.0MS/s 20.0ns/pt
A Ch1 / 1.0V
Oscillation with too high ESR (CQ)
Tek
Stopped
60 Acqs
26 Jun 13 10:13:08
An overvoltage suppressor diode can be used to further
suppress any high voltage beyond the maximum rating of
the linear voltage regulator and protect the device against
any damage due to overvoltage.
3
For linear voltage regulators with an NPN bipolar or a
MOSFET power stage, a reverse polarity diode is mandatory
to protect the device from damage due to reverse polarity.
Though the regulators with a PNP power stage have
internal reverse polarity protection, a reverse polarity
diode is still recommended in order to avoid damage due
to excessively high reverse voltage, e.g. the ISO pulse 1. The
reverse polarity diode can be put anywhere on the module
between the battery and the input pin of the regulator. It
can also be shared with other elements on the module.
4
2
VQ
Old voltage regulator only
Ch2 100mV
Oscillation with too low ESR (CQ)
24
M 400µs 500KS/s 2.0µs/pt
A Ch1 / 1.0V
Application Details
Drop-out voltage and tracking area
Drop-out voltage
Drop-out voltage is the minimum voltage differential
between the input and output required for regulation.
Regarding Infineon’s datasheet definition, it is determined
when output voltage has dropped 0.1V from its nominal
value.
500
IQ = 400mA
450
The graph below illustrates the tracking and regulating
area of a linear regulator while the input voltage rises
slowly during the start-up.
Vdr [mV]
400
350
Tracking area
When the input voltage is below the required minimum
voltage, the linear regulator is not able to regulate the
output voltage at its nominal value. However, as long as the
input voltage is beyond a switching voltage threshold to
turn the device off, the linear regulator is trying to maintain
the output voltage. The output voltage is equal to VI – Vdr.
This input voltage range is known as the tracking area,
since the output voltage is following the input.
IQ = 300mA
300
250
VI
200
IQ = 100mA
150
Tracking area:
VQ follows VI
100
IQ = 10mA
50
0
-40
0
40
80
Vdr = (VI - VQ)
@ (VQ,nom - 0.1V)
Regulation area:
VQ stabilized to VQ,nom
120
160
Tj [°C]
VQ,nom
Drop out voltage:
Vdr = VI - VQ
within tracking area,
measured @ VQ,nom - 0.1V
Typical drop-out voltage graphs (TLE42754)
Minimum input voltage
To regulate the output voltage at its nominal value, linear
regulators require a minimum input voltage which is
the nominal output voltage plus the maximum drop-out
voltage (VQ,nom + Vdr,max).
For example, consider a 5V regulator with a drop-out
voltage of max. 0.5V. The minimum input voltage required
for the 5V output is 5.5V.
In the datasheet this value is specified as the minimum
value for the input voltage and can be found under
functional range.
Example: TLE42754 input voltage range
Parameter
Input voltage
Symbol
VI
Limit values
Min.
Max.
5.5
42
Unit
V
t
Tracking
Regulating
Tracking area and drop-out voltage
Extended input voltage range
The newest Infineon linear voltage regulators start
tracking at as low as 3.3V, which meets the requirement
of cold cranking for automotive applications. The whole
input voltage range, including the tracking area and the
regulation area, is now specified as “Extended Input
Voltage Range” in the datasheet.
Example: TLF80511 input voltage range
Conditions
–
Parameter
Symbol
Limit values
Min.
Max.
Unit
Conditions
Input voltage range
for normal operation
VI
VQ, nom + Vdr
40
V
–
Extended input
voltage range
VI,ext
3.3
40
V
1)
1) Between min. value and VQ.nom + Vdr : VQ = VI − Vdr.
Below min. value: VQ = 0V
25
Application Details
Load transients
Every linear voltage regulator has an integrated control
loop regulating output voltage. Different concepts of
control loop can be implemented depending on the
application. However, every regulation loop has a certain
reaction time to adapt to load current variations. In a
short period of time, the control loop is not able to react.
It takes a minimum time for the voltage regulator to react
and to set the output voltage back to its nominal value
by adjusting the output current. In other words, voltage
variations at the regulator’s output are inevitable for a
short time during current transient.
Typical application case: supply for a microcontroller
The current consumption of a microcontroller is usually
less than 1mA in standby mode and from several 10mA
up to a few 100mA in normal operating mode. In its
application, the microcontroller is triggered from standby
mode to normal operating mode or vice versa. A fast
current transient is respectively rising or falling in 1µs at the
voltage regulator’s output.
The typical behavior of a linear voltage regulator at these
current transients is shown in the figures below.
IQ
Potential risks of big voltage variations are:
„„ Triggering an unwanted reset.
„„ Malfunction of the supplied microcontroller by exceeding
its operating range.
„„ Damage of load by exceeding its maximum ratings.
To avoid big output voltage variations, basically two
solutions are possible:
„„ Avoid big load current transients whenever possible.
The designer should first of all try to avoid big current
transients within the application.
„„ Increase the value of the output capacitor to buffer the
voltage regulator’s output voltage.
In case big load current transients are not avoidable,
increasing the output capacitance can lower the voltage
variations at load current transients and avoid the risks.
The following pictures show the output voltage deviation
of the TLE42754 at a load current transient from 1mA to
200mA with 22µF and 100µF output capacitors. Whereas
a voltage drop of 180mV has been recorded with a 22µF
output capacitor, the drop is reduced to only 85mV with a
100µF output capacitor.
Tek
Run
Hi Res
19 Jun 13 15:44:34
70mA
CQ = 22µF
2
1mA
VQ
t [µs]
Max. voltage
∆V
5V
200mA
t [µs]
Reaction time
IQ
3
70mA
IQ
1mA
Ch3 200mV
1mA
Ch2 100mV
M 40.0µs 125MS/s 8.0ns/pt
A Ch3 / 104mV
t [µs]
VQ
5V
TLE42754 output voltage deviation at load transient with a
22µF output capacitor
∆V
Min. voltage
Reaction time
Output voltage deviation at load transient
26
∆VQ = 180mV
VQ
t [µs]
Application Details
Tek
Run
Hi Res
19 Jun 13 16:01:13
CQ = 100µF
2
The overshoot level during the start-up is dependent on the
load current and the output capacitor.
The effect of the output capacitor on the voltage overshoot
is shown in the following graphs:
VQ
∆VQ = 85mV
Tek
Run
Hi Res
21 Jun 13 13:57:03
14V
200mA
3
IQ
VQ,peak = 5.47V
1mA
3
Ch3 200mV
Ch2 100mV
VI
0V
M 40.0µs 125MS/s 8.0ns/pt
A Ch3 / 104mV
TLE42754 output voltage deviation at load transient with a 100µF output
capacitor
2
VQ
CQ = 22µF
To dimension the output capacitor reasonably, the
following steps are recommended:
„„ Check for worst-case current transients within the
application.
„„ Define max. allowed voltage variation ΔVmax during
current transient.
„„ Determine the voltage variation ΔV of the voltage
regulator at the worst-case current transient with the
minimum output capacitance fulfilling the requirement
for stability.
„„ If ΔV is higher than ΔVmax, try with a bigger output
capacitance.
„„ Choose an output capacitor which ensures the voltage
variation ΔV is within the allowed range.
„„ Verify the selected output capacitor on the application
hardware.
Ch3 5.0V
Ch2 1.0V
M 200µs 25.0MS/s 40.0ns/pt
A Ch3 / 2.8V
TLF42754 output voltage deviation at load transient with a 22µF output
capacitor
Tek
Stopped
1 Acqs
21 Jun 13 13:48:04
14V
VQ,peak = 5.25V
3
2
VI
0V
VQ
CQ = 100µF
Overshoot at start-up
During the start-up, i.e. while the input voltage is powered
on, the linear voltage regulator is driving the maximum
output current to charge the output capacitor and raise
the output voltage to the nominal value. When the nominal
output voltage is reached, the control loop of the linear
voltage regulator needs a few microseconds to react.
During these few microseconds, the regulator is still
charging the output cap, leading to a further increase of the
output voltage. After those few microseconds, the regulator
starts regulating the output voltage to the nominal voltage.
Ch3 5.0V
Ch2 1.0V
M 200µs 25.0MS/s 40.0ns/pt
A Ch3 / 2.8V
TLF42754 output voltage deviation at load transient with a 100µF output
capacitor
To smooth out voltage overshoot on start-up, two measures
are recommended:
„„ Increase the capacitor value at the input to slow down
the slope of the input voltage.
„„ Increase the output capacitor value to slow down the
slope of the output voltage.
27
Application Details
PCB layout
Below is an example of a good PCB layout design:
The PCB layout design is important for the performance of
a linear voltage regulator. A good PCB layout can optimize
the performance, whereas a poor one may impact on the
stable operation of the regulator and introduce various
disturbances in the system.
Here are some general recommendations for the PCB
design with a linear voltage regulator:
„„ Place the output capacitor as close as possible to the
regulator’s output and GND pins and on the same side of
the PCB as the regulator.
„„ Place the ceramic input capacitor (e.g. 100nF) as close
as possible to the regulator’s input pin and on the same
side of the PCB as the regulator.
„„ Place the larger input buffer capacitor (e.g. 10µF) on the
same PCB.
„„ Traces connected to the regulator’s input and output
should be sized according to the current flowing through
it.
„„ Ensure a good GND connection.
„„ For 4 or more layer PCBs, use one middle layer for GND
and place sufficient number of vias to GND layer.
„„ For a 1 or 2 layer PCB, place a sufficient GND plane.
The PCB layout design is also crucial to the thermal
performance. Here are some recommendations for a good
thermal design:
„„ Ensure good thermal connection.
„„ Place sufficient cooling area depending on the power
dissipation.
„„ For 4 or more layer PCBs, place sufficient number of
thermal vias to the thermal layer.
„„ Put other heat sources on the board as far away as
possible from the position of the linear voltage regulator.
28
GND plane
GND vias
Output capacitor
Input capacitor
3
1
4
Input pin
Output pin
3
3
2
1
2
4
LDO
Thermal vias
5
6
PCB layout example
Application Schematic
Application Schematic
VBAT
Linear voltage regulator
I
e.g.
Ignition EN
Q
Regulated output voltage
R1
RRA1
RRO
RWO
RSO
VA
Internal
supply
CQ
Load
(e. g.
Microcontroller)
RO
RSI1
Protection
circuits
CI
Bandgap
reference
Reset
and
watchdog
generator
WO
WI
RADJ
SO
SI
GND
RSI2
D
R2
CD
GND
RRA2
General application schematic for bipolar voltage regulators with analog reset and watchdog timing control
Linear voltage regulator
VBAT
Q
I
e.g.
Ignition EN
Regulated output voltage
R1
Internal
supply
CQ
Protection
circuits
RSO
Bandgap
reference
Reset
and
watchdog
generator
WO
WI
WM1/2
SO
SI
RSI2
RWO
Load
(e. g.
Microcontroller)
RO
RSI1
CI
RRO
VA
GND
R2
GND
General application schematic for MOSFET voltage regulators with digital reset and watchdog timing control
29
Packages
Packages
30
PG-DSO-8
PG-DSO-8 (Exposed Pad)
PG-DSO-14
PG-DSO-20
PG-DSO-20 (Power-SO)
SCT595
SOT223
PG-SSOP-14EP
PG-TO252-3 (DPAK)
PG-TO252-5 (DPAK-5-leg)
PG-TO263-3 (TO220-3 (SMD))
PG-TO263-5 (TO220-5 (SMD))
PG-TO263-7 (TO220-7 (SMD))
TSON-10
Glossary
Glossary
ADJ
CD
CI
CQ
D
EN
ESR
I
ID,wd,max
INH
Iq
IQ,MAX
Iq,steady
Adjustable output
Delay capacitor
Input capacitor
Output capacitor
Delay capacitor pin for reset and watchdog
Enable pin
Equivalent series resistance
Input pin
Maximum watchdog discharge current
Inhibit pin (ref. EN)
Quiescent current
Maximum output current
Steady state quiescent current
PD
Power dissipation
Psteady Steady state power
Q
Output pin
QADJ
Adjustable output pin
R1
Output voltage adjust resistor 1
R2
Output voltage adjust resistor 2
RADJ
Reset threshold adjust pin
RADJ,1
Reset threshold adjust resistor 1
RADJ,2
Reset threshold adjust resistor 2
RO
Reset output pin
RPU,D
Pull-up resistor at D pin for watchdog
Deactivation
RRO
Reset output internal pull-up resistor
RRO,ext Reset output external pull-up resistor
RSI1
Sense input voltage divider resistor 1
RSI2
Sense input voltage divider resistor 2
RthJA
Junction to ambient thermal resistance
RthJC
Junction case thermal resistance
RWO,ext Watchdog output external pull-up resistor
SI
Sense input pin
SO
Sense output pin
Ta
Ambient temperature
Tj
Junction temperature
Tj,max
Maximum junction temperature
Tj,sd
Thermal shutdown junction temperature
Tj,shd
Thermal shutdown junction temperature
Hysteresis
Tj,steady Steady state junction temperature
trd
Power-on reset delay time
trd,100nF Power-on reset delay time with 100nF
Capacitor
trr
Reset reaction time
trr,d,100nF Reset reaction time delay with 100nF
Capacitor
trr,int
Internal reset reaction time
tSTARTUP Start-up time
tWD,low
VA
VBAT
VD
VDD
VDL
VDU
VI
VI,TH
VQ
VQ,nom
Vref
VRO
VRT
VSI
VWI
VWO
WI
WM1
WM2
WO
ZthJA
Low watchdog time
Voltage adjust pin
Battery voltage
Voltage at D pin
Supply pin of microcontroller
Delay capacitor lower threshold
Delay capacitor upper threshold
Input voltage
Threshold trigger the early warning
Output voltage
Nominal output voltage
Internal reference voltage
Reset output voltage
Reset threshold
Sense input voltage
Watchdog input voltage
Watchdog output voltage
Watchdog input pin
Watchdog mode Selection Pin 1
Watchdog mode Selection Pin 2
Watchdog output
Junction ambient thermal impedance
31
Ask Infineon. Get connected with the answers.
Infineon offers its toll-free 0800/4001 service hotline as one central number,
available 24/7 in English, Mandarin and German.
Our global connection service goes way beyond standard switchboard
services by offering qualified support on the phone. Call us!
„„ Germany ................... 0800 951 951 951 (German/English)
„„ China, mainland ....... 4001 200 951 (Mandarin/English)
„„ India .......................... 000 800 4402 951 (English)
„„ USA ............................ 1-866 951 9519 (English/German)
„„ Other countries ......... 00* 800 951 951 951 (English/German)
„„ Direct access ............. +49 89 234-0 (interconnection fee, German/English)
* Please note: Some countries may require you to dial a code other than “00” to access this international number,
please visit www.infineon.com/service for your country!
Where to Buy
Infineon Distribution Partners and
Sales Offices:
www.infineon.com/WhereToBuy
Stay connected
www.facebook.com/infineon
Mobile Product Catalog
Mobile app for iOS and Android.
www.google.com/+infineon
www.twitter.com/infineon
www.infineon.com/linkedin
www.infineon.com/xing
www.youtube.com/infineon
Infineon Technologies – innovative semiconductor solutions for energy efficiency, mobility and security.
Published by
Infineon Technologies AG
85579 Neubiberg, Germany
© 2014 Infineon Technologies AG.
All Rights Reserved.
Visit us:
www.infineon.com
Order Number: B124-H9919-X-X-7600
Date: 07 / 2014
Attention please!
The information given in this document shall in no event
be regarded as a guarantee of conditions or characteristics
(“Beschaffenheitsgarantie”). With respect to any examples
or hints given herein, any typical values stated herein and/
or any information regarding the application of the device,
Infineon Technologies hereby disclaims any and all warranties and liabilities of any kind, including without limitation
warranties of non-infringement of intellectual property
rights of any third party.
Information
For further information on technology, delivery terms and
conditions and prices please contact your nearest Infineon
Technologies Office (www.infineon.com).
Warnings
Due to technical requirements components may contain
dangerous substances. For information on the types in
question please contact your nearest Infineon Technologies
Office. Infineon Technologies Components may only be
used in life-support devices or systems with the express
written approval of Infineon Technologies, if a failure of
such components can reasonably be expected to cause
the failure of that life-support device or system, or to affect
the safety or effectiveness of that device or system. Life
support devices or systems are intended to be implanted in the human body, or to support and/or maintain and
sustain and/or protect human life. If they fail, it is reasonable
to assume that the health of the user or other persons may
be endangered.