LinkSwitch-TN2
Family
for Automotive
Highly Energy Efficient Switcher IC with Integrated System
Level Protection for Low Component-Count Power Supplies
Product Highlights
Highest Performance and Design Flexibility
•
•
•
•
•
•
•
•
•
•
•
•
Supports buck, buck-boost and flyback topologies
Wide input voltage 30 VDC to 550 VDC
Excellent load and line regulation
66 kHz operation with accurate current limit
•
Allows the use of low-cost off-the-shelf inductors
• Reduces size and cost of magnetics and output capacitor
Frequency jittering reduces EMI filter complexity
Pin-out simplifies PCB heat sinking
AEC-Q100 qualified
Fab and assembly are IATF16949 certified
FB
BP/M
S
30 - 550
VDC
+
LinkSwitch-TN2
D
DC
Output
+
PI-7841l-061522
Enhanced Safety and Reliability Features
Figure 1.
Auto-restart for short-circuit and open loop faults
Output overvoltage protection (OVP)
Hysteretic over-temperature protection (OTP)
Extended creepage between DRAIN pin and all other pins improves
field reliability
• 750 V MOSFET rating for excellent surge withstand
Typical Buck Converter Application (See Application Examples
Section for Other Circuit Configurations).
EcoSmart
™
– Extremely Energy Efficient
•
•
•
•
Standby supply current <100
μA
On/Off control provides constant efficiency over a wide load range
Easily meets all global energy efficiency regulations
No-load consumption <50 mW
Figure 2.
Package Option G: SMD-8C.
Application
• Auxiliary power supplies for automotive HVAC, climate control,
DC/DC converter, and onboard charger
• Emergency power supply for traction inverter
Output Current Table
1
Product
2
LNK3206GQ
LNK3209GQ
30 VDC
270 mA
650 mA
400 VDC
360 mA
850 mA
Description
The LinkSwitch™-TN2 family of ICs for automotive power supplies
provide significant reduction in component count compared to
traditional discrete solutions making it highly reliable. The device family
supports buck, buck-boost and flyback converter topologies. Each
device incorporates a 750 V power MOSFET, oscillator, On/Off control, a
high-voltage switched current source for self-biasing, frequency jittering,
fast (cycle-by-cycle) current limit, hysteretic thermal shutdown, and
output and overvoltage protection circuitry onto a monolithic IC.
LinkSwitch-TN2 ICs consume very little current in standby resulting in
power supply designs that meet <50 mW no-load input at 400 VDC
input. A full suite of protection features enable safe and reliable power
supplies protecting the device and the system against input and output
overvoltage faults, device over-temperature faults, lost regulation, and
power supply output overload or short-circuit faults.
Table 1.
Output Current Table.
Notes:
1. Typical output current in a non-isolated buck converter with devices operating
at default current limit and adequate heat sinking. Output power capability
depends on respective output voltage and thermal requirements.
2. Package: G: SMD-8C.
www.power.com
June 2022
This Product is Covered by Patents and/or Pending Patent Applications.
LinkSwitch-TN2
BYPASS
(BP/M)
REGULATOR
5.0 V
I
FBSD
I
FB
5.2 V
AUTO-RESTART
COUNTER
CLOCK
RESET
5.0 V
4.5 V
FAULT
PRESENT
BYPASS PIN
CAPACITOR
DETECT
+
-
DRAIN
(D)
OVL
BYPASS PIN
UNDERVOLTAGE
CURRENT LIMIT
COMPARATOR
+
-
VI
LIMIT
JITTER
CLOCK
DC
MAX
OSCILLATOR
THERMAL
SHUTDOWN
S
FEEDBACK
(FB)
2.0 V -V
T
R
Q
Q
LEADING
EDGE
BLANKING
OVP
DETECT
SOURCE
(S)
PI-7879-020819
Figure 3.
Functional Block Diagram.
Pin Functional Description
DRAIN (D) Pin:
Power MOSFET drain connection. Provides internal operating current
for both start-up and steady-state operation.
BYPASS (BP/M) Pin:
This pin has multiple functions:
• It is the connection point for an external bypass capacitor for the
internally generated 5.0 V supply.
• It is a mode selector for the current limit value, depending on the
value of the capacitance added. Use of a 0.1
μF
capacitor results
in the standard current limit value. Use of a 1
μF
capacitor results
in the current limit being reduced, allowing design with lowest cost
surface mount buck chokes.
•
It provides a shutdown function. When the current into the BYPASS
pin exceeds I
BP(SD)
for a time equal to 2 to 3 cycles of the internal
oscillator (f
OSC
), the device enters auto-restart. This can be used to
provide an output overvoltage protection function with external
circuitry.
FEEDBACK (FB) Pin:
During normal operation, switching of the power MOSFET is
controlled by the FEEDBACK pin. MOSFET switching is terminated
when a current greater than I
FB
(49
μA)
is delivered into this pin. Line
overvoltage protection is detected when a current greater than I
FB(SD)
is delivered into this pin for 2 consecutive switching cycles.
SOURCE (S) Pin:
This pin is the power MOSFET source connection. It is also the
ground reference for the BYPASS and FEEDBACK pins.
G Package (SMD-8C)
BP/M
FB
1
2
8
7
6
D
4
5
S
S
S
S
PI-5910b-102319
Figure 4.
Pin Configuration.
2
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Rev. D 06/22
LinkSwitch-TN2
PI-3660-081303
LinkSwitch-TN2 Functional Description
LinkSwitch-TN2 combines a high-voltage power MOSFET switch with
a power supply controller in one device. Unlike conventional PWM
(pulse width modulator) controllers, LinkSwitch-TN2 uses a simple
ON/OFF control to regulate the output voltage. The LinkSwitch-TN2
controller consists of an oscillator, feedback (sense and logic) circuit,
5.0 V regulator, BYPASS pin undervoltage circuit, over-temperature
protection, line and output overvoltage protection, frequency jittering,
current limit circuit, leading edge blanking and a 750 V power MOSFET.
The LinkSwitch-TN2 incorporates additional circuitry for auto-restart.
Oscillator
The typical oscillator frequency is internally set to an average of f
OSC
(66 kHz). Two signals are generated from the oscillator: the maximum
duty cycle signal (DC
MAX
) and the clock signal that indicates the
beginning of each cycle.
The LinkSwitch-TN2 oscillator incorporates circuitry that introduces a
small amount of frequency jitter, typically 4 kHz peak-to-peak, to
minimize EMI emission. The modulation rate of the frequency jitter is
set to 1 kHz to optimize EMI reduction for both average and quasi-
peak emissions. The frequency jitter should be measured with the
oscilloscope triggered at the falling edge of the DRAIN waveform. The
waveform in Figure 5 illustrates the frequency jitter of the LinkSwitch-TN2.
Soft-Start
At power-up or during a restart attempt in auto-restart, the device
applies a soft-start by temporarily reducing the oscillator frequency.
LNK3206GQ reduces the frequency to f
OSC(SS)
(typically 33 kHz).
LNK3209GQ reduces the oscillator frequency to initially 16.5 kHz
followed by a stepwise increase to 22 kHz and 33 kHz over a period
of 256 switching cycles. Soft-start terminates and the device
continues operating at the nominal oscillator frequency f
OSC
either
after 256 switching cycles or if the output voltage reaches regulation.
Feedback Input Circuit
The feedback input circuit at the FEEDBACK pin consists of a low
impedance source follower output set at V
FB
(2.0 V). When the
current delivered into this pin exceeds I
FB
(49
μA),
a low logic level
(disable) is generated at the output of the feedback circuit. This
output is sampled at the beginning of each cycle on the rising edge
of the clock signal. If high, the power MOSFET is turned on for that
cycle (enabled), otherwise the power MOSFET remains off (disabled).
The sampling is done only at the beginning of each cycle. Subse-
quent changes in the FEEDBACK pin voltage or current during the
remainder of the cycle do not impact the MOSFET enable/disable
status. If a current greater than I
FB(SD)
is injected into the FEEDBACK
pin while the MOSFET is enabled for at least two consecutive cycles
the part will stop switching and enter auto-restart off-time. Normal
switching resumes after the auto-restart off-time expires.
5.0 V Regulator and 5.2 V Shunt Voltage Clamp
The 5.0 V regulator charges the bypass capacitor connected to the
BYPASS pin to V
BP
by drawing a current from the voltage on the
DRAIN, whenever the MOSFET is off. The BYPASS pin is the internal
supply voltage node for the LinkSwitch-TN2. When the MOSFET is
on, the LinkSwitch-TN2 runs off of the energy stored in the bypass
capacitor. Extremely low power consumption of the internal circuitry
allows the LinkSwitch-TN2 to operate continuously from the current
drawn from the DRAIN pin. A bypass capacitor value of 0.1
μF
is
sufficient for both high frequency decoupling and energy storage.
In addition, there is a shunt regulator clamping the BYPASS pin
at
V
BP(SHUNT)
(5.2 V) when current is provided to the BYPASS pin through
an external resistor. This facilitates powering of LinkSwitch-TN2
externally through a bias winding to decrease the no-load consump-
tion to about 10 mW. The device stops switching instantly and enters
auto-restart when a current ≥I
BP(SD)
is delivered into the BYPASS pin.
600
500
V
DRAIN
400
300
200
100
0
68 kHz
64 kHz
0
Time (µs)
Figure 5.
Frequency Jitter.
20
BYPASS Pin Undervoltage
The BYPASS pin undervoltage circuitry disables the power MOSFET
when the BYPASS pin voltage drops below V
BP
– V
BP(H)
(approximately
4.5 V). Once the BYPASS pin voltage drops below this threshold, it
must rise back to V
BP
to enable (turn-on) the power MOSFET.
Over-Temperature Protection
The thermal shutdown circuitry senses the die temperature. The
threshold is set at T
SD
(142 °C typical) with a 30 °C (T
SD(H)
) hysteresis.
When the die temperature rises above T
SD
the power MOSFET is
disabled and remains disabled until the die temperature falls to
T
SD
– T
SD(H)
, at which point it is re-enabled.
Current Limit
The current limit circuit senses the current in the power MOSFET.
When this current exceeds the internal threshold (I
LIMIT
), the power
MOSFET is turned off for the remainder of that cycle. The leading
edge blanking circuit inhibits the current limit comparator for a short
time (t
LEB
) after the power MOSFET is turned on. This leading edge
blanking time has been set so that current spikes caused by capaci-
tance and rectifier reverse recovery time will not cause premature
termination of the switching pulse. Current limit can be selected using
the BYPASS pin capacitor (0.1
μF
for normal current limit / 1
μF
for
reduced current limit). LinkSwitch-TN2 selects between normal and
reduced current limit at power-up prior to switching.
Auto-Restart
In the event of a fault condition such as output overload, output
short, or an open-loop condition, LinkSwitch-TN2 enters into
auto-restart operation. An internal counter clocked by the oscillator
gets reset every time the FEEDBACK pin is pulled high. If the
FEEDBACK pin is not pulled high for t
AR(ON)
(50 ms), the power
MOSFET switching is disabled for a time equal to the auto-restart
off-time. The first time a fault is asserted the off-time is 150 ms
(t
AR(OFF)
first off period). If the fault condition persists, subsequent
off-times are 1500 ms long (t
AR(OFF)
subsequent periods). The
auto-restart alternately enables and disables the switching of the
power MOSFET until the fault condition is removed. The auto-restart
counter is gated by the switch oscillator.
3
www.power.com
Rev. D 06/22
LinkSwitch-TN2
Hysteretic Output Overvoltage Protection
The output overvoltage protection provided by the LinkSwitch-TN2 IC
uses auto-restart that is triggered by a current >I
BP(SD)
into the BYPASS
pin. In addition to an internal filter, the BYPASS pin capacitor forms
an external filter providing noise immunity from inadvertent triggering.
For the bypass capacitor to be effective as a high frequency filter, the
capacitor should be located as close as possible to the SOURCE and
BYPASS pins of the device.
The OVP function can be realized in a flyback converter by connect-
ing a Zener diode from the output supply to the BYPASS pin. The
circuit example shown in Figure 6 describes a simple method for
implementing the output overvoltage protection. Adding additional
filtering can be achieved by inserting a low value (10
Ω
to 47
Ω)
resistor in series with the OVP Zener diode. The resistor in series
with the OVP Zener diode also limits the maximum current into the
BYPASS pin. The current should be limited to less than 16 mA.
During a fault condition resulting from loss of feedback, the output
voltage will rapidly rise above the nominal voltage. A voltage at the
output that exceeds the sum of the voltage rating of the Zener diode
connected from the output to the BYPASS pin and bypass voltage,
will cause a current in excess of I
BP(SD)
injected into the BYPASS pin,
which will trigger the auto-restart and protect the power supply from
overvoltage.
T1
V
O
+
V
BUS
D
FB
BP
S
+
V
OV
= V
BP
+ V
DOVP
R
BP
D
OVP
PI-8024-092916
LinkSwitch-TN2
C
BP
Figure 6.
Non-Isolated Flyback Converter with Output Overvoltage Protection.
4
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Rev. D 06/22
LinkSwitch-TN2
Applications Example
R2
16.5 kΩ
1%
1/16 W
R3
35.7 kΩ
1%
1/8 W
V
IN+
F1
1.25 A
FB
D
BP/M
S
C2
0.1
µF
50 V
R1
2.49 kΩ
1%
1/16 W
C3
10
µF
35 V
L1
SRF1280A-102M
D3
RS1MLR3G
1000 V
15 V,
300 mA
+V
LinkSwitch-TN2
U1
LNK3206GQ
30 - 550
VDC
C1
0.1
µF
630 VDC
D1
UF1JLWHRVG
600 V
D2
UF1JLWHRVG
600 V
C4
220
µF
25 V
R4
15 kΩ
1/8 W
V
IN-
PI-9137c-061422
GND
Figure 7.
30 VDC – 550 VDC, 15 V, 300 mA Constant Voltage Power Supply using LinkSwitch-TN2 Automotive.
30 VDC – 550 VDC Input 4.5 W Buck Converter
The circuit shown in Figure 7 is typical implementation of a 15 V,
300 mA non-isolated power supply used in automotive application.
DC voltage from a battery source will be the input to the buck
converter. The buck converter circuit was designed to meet
AEC-Q100 Grade 3 temperature requirement of -40 °C to +85 °C.
The input stage comprises of fuse F1 and capacitor C1. In the event
of fault condition, Fuse F1 will break open from the input supply for
catastrophic event within the buck converter circuit. Capacitor C1
serves as a decoupling capacitor which helps to provide local
instantaneous charge to the buck converter.
The LinkSwitch-TN2 automotive IC, freewheeling diode D1 and D2,
output choke L1, and the output capacitor C4, forms the power
processing stage. The power supply operates in mostly continuous-
mode (MCM) due to the output load current requirement. Since
application’s maximum ambient temperature is 85 °C, diode D1 and
D2 are ultrafast diode with a reverse recovery time (t
RR
) of approxi-
mately 25 ns. Inductor L1 is a standard off-the-shelf inductor with
appropriate RMS current rating (and acceptable temperature rise).
Capacitor C4 is the output filter capacitor; its primary function is to
filter the output voltage ripple. The output voltage ripple is a
stronger function of the ESR of the output capacitor than the value of
the capacitor itself. Optional resistor R3 supplies the BYPASS pin
externally for significantly lower no-load input power and increased
efficiency over all load conditions.
The voltage developed across C3 is sensed and regulated via the
resistor divider R1 and R2 connected to U1’s FEEDBACK pin. The
values of R1 and R2 are selected such that, at the desired output
voltage, the voltage at the FEEDBACK pin is 2.00 V.
Regulation is maintained by skipping switching cycles. As the output
voltage rises, the current into the FEEDBACK pin will rise. If this
exceed I
FB
then subsequent cycle will be skipped until the current is
reduces below I
FB
. Thus, as the output load is reduced, more cycles
will be skipped and if the load increases, fewer cycles are skipped.
To provide overload protection if no cycles are skipped during 50 ms
period, LinkSwitch-TN2 Automotive will enter auto-restart, limiting the
average output power to approximately 3% of the maximum overload
power. Due to tracking errors between the output voltage and the
voltage across C3 at light load or no-load, a small pre-load may be
required (R4). For the design in Figure 7, if regulation to zero load is
required, then this value should be reduced to 5 kΩ.
5
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Rev. D 06/22
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