Power LCS700 Integrated llc controller, high-voltage power mosfets and driver Datasheet

LCS700-708
HiperLCS™ Family
Integrated LLC Controller, High-Voltage
Power MOSFETs and Drivers
Product Highlights
Features
• LLC half-bridge power stage incorporating controller, high and
low-side gate drives, and high-voltage power MOSFETs
• Eliminates up to 30 external components
• High maximum operating frequency of 1 MHz
• Nominal steady-state operation up to 500 kHz
• Dramatically reduces magnetics size and allows use of
SMD ceramic output capacitors
• Precise duty symmetry balances output rectifier current,
improving efficiency
• 50% ±0.3% typical at 300 kHz
• Comprehensive fault handling and current limiting
• Programmable brown-in/out thresholds and hysteresis
• Undervoltage (UV) and overvoltage (OV) protection
• Programmable over-current protection (OCP)
• Short-circuit protection (SCP)
• Over-temperature protection (OTP)
• Programmable dead-time for optimized design
• Programmable burst mode maintains regulation at no-load and
improves light load efficiency
• Programmable soft-start time and delay before soft-start
• Accurate programmable minimum and maximum frequency
limits
• Single package designed for high-power and high-frequency
• Reduces assembly cost and reduces PCB layout loop areas
• Simple single clip attachment to heat sink
• Exposed thermal pad connected to ground potential – no
insulators required between package and heat sink
• Staggered pin arrangement for simple PC board routing
and high-voltage creepage requirements
• Paired with HiperPFS PFC product gives complete, high
efficiency, low part count PSU solutions
Applications
• High-efficiency power supplies (80 PLUS Silver, Gold and
Platinum)
• LCD TV power supplies
• LED street and area lighting
• Printer power supplies
• Audio amplifier
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Description
The HiperLCS is an integrated LLC power stage incorporating a
multi-function controller, high-side and low-side gate drivers,
plus two power MOSFETs in a half-bridge configuration. Figure
1 shows a simplified schematic of a HiperLCS based power stage
where the LLC resonant inductor is integrated into the transformer.
The variable frequency controller provides high efficiency by
switching the power MOSFETs at zero voltage (ZVS), eliminating
switching losses.
B+
D
VCCH
Standby
Supply
HV DC
Input
VCC
CONTROL
+V
HB
OV/UV
VREF
RTN
RFMAX
DT/BF
IS
HiperLCS
RBURST
FB
B-
G
S1/S2
LLC Feedback Circuit
Figure 1.
PI-6159-060211
Typical Application Circuit – LCD TV and PC Main Power Supply.
Output Power Table
Product
Maximum Practical Power1
LCS700HG
110 W
LCS701HG
170 W
LCS702HG
220 W
LCS703HG
275 W
LCS705HG
350 W
LCS708HG
440 W
Table 1. Output Power Table.
Notes:
1. Maximum practical power is the power the part can deliver when properly
mounted to a heat sink and a maximum heat sink temperature of 90 °C.
June 2011
LCS700-708
VCC
VREF
DRAIN (D)
3.4 V
REGULATOR
UVLO
VCCH
LLC_ON
+
OV/UV
VSDH/
VSDL
UVLO
SOFT-START DELAY
131,072 LLC
CLOCK CYCLES
DEBOUNCE
3 LLC CLOCK
CYCLES
+
VOVH/
VOVL
OVERTEMPERATURE
PROTECTION
+
IS
HB
LEVEL
SHIFT
VISF
7 CONSECUTIVE
LLC CLOCK
CYCLES
+
VISS
LLC_CLK
VREF
FEEDBACK (FB)
LLC
CLOCK
DT/BF
+
DT/BF
RESISTOR
SENSOR
DEAD-TIME
GENERATOR
OUTPUT
CONTROL
LOGIC
DEBOUNCE
3 LLC CLOCK
CYCLES
Bursting
Thresholds
Control
GROUND (G)
Figure 2.
PI-5755-060111
SOURCE (S1/S2)
Block Diagram.
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Rev. B 062011
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LCS700-708
Pin Functional Description
H Package (eSIP-16C)
OV/UV Pin
Overvoltage/Undervoltage pin. B+ is sensed by this pin through
a resistor divider. The OV/UV pin implements brown-in,
brown-out, and overvoltage lockout with hysteresis. Pulling this
pin down to ground will implement a remote-off function.
FEEDBACK (FB) Pin
Current fed into this pin determines LLC switching frequency;
higher current programs higher switching frequency. The pin
V-I characteristic resembles a diode to ground during normal
switching. An RC network between the VREF pin and
FEEDBACK pin determines the minimum operating frequency,
start-up frequency, soft-start time, and delay before start-up.
DEAD-TIME/BURST FREQUENCY (DT/BF) Pin
A resistor divider from VREF to ground programs dead-time,
maximum switching frequency at start-up, and burst-mode
threshold frequencies.
CURRENT-SENSE (IS) Pin
The CURRENT-SENSE pin is used for sensing transformer
primary current, to detect overload and fault conditions, through
a current sense resistor or a capacitive divider plus sense resistor
circuit. It resembles a reverse diode to ground, and does not
require a rectifier circuit for preventing negative pulses from
reaching the pin, provided the reverse current is limited to <5 mA.
G
G
NC
VCCH
D
GROUND (G) Pin
G is the return node for all analog small signals. All small signal
pin bypass capacitors must be returned to this pin through short
traces, with the exception of the D-S high-voltage bypass
capacitor, and the VCCH bypass capacitor. It is internally
connected to the SOURCE pins to provide a star connection.
Do not connect the GROUND pin to the SOURCE pins,
nor to the B- bus, in the PCB layout.
VCCH
HB
D
3 4 5 6 7 8 9 1011 13 14 16
S2
S1
NC
IS
DT/BF
FB
OV/UV
G
VREF
VCC
VREF Pin
3.4 VREF pin. An internal voltage reference network used as a
voltage source for FEEDBACK pin and DT/BF pin pull-up
resistor.
Exposed Metal
(On Package Edge)
1
Internally
Connected
D
Note: The system standby supply return should be connected to
the B- bus and not to the GROUND pin.
HB
VCC Pin
IC power pin. In a typical application, VCC is connected to the
12 V system standby supply via a 5 W resistor. This resistor
helps provide filtering and improves noise immunity.
Exposed Pad
(Backside) Internally
Connected to GROUND
Pin (see eSIP-16C
Package Drawing)
PI-5636-051311
Figure 3.
Pin Numbering and Designation.
SOURCE (S1), (S2) Pins
SOURCE pins of internal low-side MOSFET. These should be
connected together on the PCB, and connected to the B- from
the PFC bulk capacitor or input high-voltage DC return.
HB Pin
This is the output of the half-bridge connected MOSFETs
(Source of high-side MOSFET, Drain of low-side MOSFET), to
be connected to the LLC power train (transformer primary and
series resonant capacitor).
VCCH Pin
Floating bootstrap supply pin for the LLC high-side driver. This
pin is referenced to the HB pin, which in turn is internally
connected to the SOURCE pin of the high-side MOSFET. A
bypass/storage capacitor between VCCH and HB pins, and a
boot strap diode with a series resistor from the standby supply,
are required. The storage capacitor is refreshed every time the
lower MOSFET turns on or its body diode conducts.
DRAIN (D) Pin
DRAIN pin of the internal high-side MOSFET. This connects to
the B+ from the PFC bulk capacitor or input high-voltage DC bus.
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Rev. B 062011
Figure 4.
Rev. B 062011
B-
C20
47 μF
35 V
+12 V
VCC
B+
380 V
R4
20 kΩ
1%
C2
4.7 nF
200 V
R3
976 kΩ
1%
R2
976 kΩ
1%
R1
976 kΩ
1%
C1
1 μF
25 V
C5
4.7 nF
200 V
R5
4.7 Ω
R19
143 kΩ
1%
R21
4.7 kΩ
C6
1 μF
25 V
U2B
LTV817A
R10
7.68 kΩ
1%
R6
2.2 Ω
D3
1N4148
R20
1.2 kΩ
R8
36.5 kΩ
1%
R9
7.68 kΩ
1%
C3
220 nF
50 V
VREF
DT/BF
OV/UV
VCC
HiperLCS
U1
LCS702HG
D1
UF4005
FB
C4
4.7 nF
200 V
G
CONTROL
VCCH
S1/S2
D
IS
HB
R12
220 Ω
C8
330 nF
50 V
C7
1 nF
200 V
C9
22 nF
630 V
R11
24 Ω
C12
47 pF
1 kV 5
1
C11
6.2 nF
1.6 kV
FL4
FL2,3
T1
EEL25.4
FL1
C13
2.2 nF
250 VAC
R14
7.5 kΩ
C15
10 μF
35 V
R23
47 Ω
U2A
LTV817A
C10
330 nF
50 V
C14
10 μF
35 V
D2
STPS30L60CT
R18
10 kΩ
1%
R13
86.6 kΩ
1%
PI-6160-062011
C17
2.2 nF
200 V
U3
LM431AIM3DR
2%
R17
22 kΩ
R15
1 kΩ
R16
1.5 kΩ
C19
3.3 nF
200 V
C16
470 μF
35 V
L1
150 nH
RTN
24 V
LCS700-708
150 W Laser-Jet Printer Power Supply.
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LCS700-708
HiperLCS Basic Operation
The HiperLCS is designed for half-bridge LLC converters, which
are high-efficiency resonant, variable frequency converters. The
HiperLCS is an LLC controller chip with built-in drivers and
half-bridge MOSFETs.
LLC converters require a fixed dead-time between switching
half-cycles. The dead-time, maximum frequency at start-up,
and burst threshold frequencies, are programmed with a resistor
divider on the DT/BF pin from the VREF to the GROUND pins.
The FEEDBACK (FB) pin is the frequency control input for the
feedback loop. Frequency is proportional to FEEDBACK pin
current. The FEEDBACK pin V-I characteristic resembles a
diode to ground.
Burst Mode
If the frequency commanded by the FEEDBACK pin current
exceeds the upper burst threshold frequency (fSTOP, ISTOP)
programmed by the resistor divider on the DT/BF pin, the output
MOSFETs will turn off, and will resume switching when the current
drops below the value which corresponds to the frequency
equal to the lower burst threshold frequency (fSTART, ISTART ). As a
first approximation, burst mode control resembles a hysteretic
controller where the frequency ramps from fSTART to fSTOP, stops
and repeats. An external component network connected from
the VREF pin to the FEEDBACK pin determines the minimum
and start-up FEEDBACK pin currents, and thus the minimum
and start-up switching frequencies. A soft-start capacitor in
this network determines soft-start timing.
The VREF pin provides a nominal 3.4 V as a reference for this
FEEDBACK pin external network and other functions. Maximum
current from this pin must be ≤4 mA.
The Dead-Time/Burst Frequency (DT/BF) pin also has a diode-toground V-I characteristic. A resistor divider from VREF to GROUND
programs dead-time, maximum start-up switching frequency (fMAX),
and the burst threshold frequencies. The current flowing from the
resistor divider to the DT/BF pin determines fMAX. The ratio of the
resistors selects from 3 discrete, burst threshold frequency ratios,
which are fixed fractions of fMAX.
The OV/UV pin senses the high-voltage B+ input through a
resistor divider. It implements brown-in, brown-out, and OV
with hysteresis. The ratios of these voltages are fixed; the user
must select the resistor divider ratio such that the brown-in
voltage is below the minimum nominal bulk (input) voltage
regulation set-point to ensure start-up, and the OV (lower)
restart voltage is above the maximum nominal bulk voltage
set-point, to ensure that the LCS will restart after a voltage swell
event that triggers the OV upper threshold. If different brown-in
to brown-out to OV ratios are required, external circuitry needs
to be added to the resistor divider.
VCC Pin UVLO
The VCC pin has an internal UVLO function with hysteresis. The
HiperLCS will not start until the voltage exceeds the VCC start
threshold VUVLO(+). HiperLCS will turn off when the VCC drops to
the VCC Shutdown Threshold VUVLO(-).
VCCH Pin UVLO
The VCCH pin is the supply pin for the high-side driver. It also
has a UVLO function similar to the VCC pin, with a threshold
lower than the VCC pin. This is to allow for a VCCH voltage that
is slightly lower than VCC because the VCCH pin is fed by a
bootstrap diode and series current-limiting resistor from the
VCC supply.
Start-Up and Auto-Restart
Before start-up the FEEDBACK pin is internally pulled up to the
VREF pin to discharge the soft-start capacitor and to keep the
output MOSFETs off. When start-up commences the internal
pull-up transistor turns off, the soft-start capacitor charges, the
outputs begin switching at fMAX, the FEEDBACK pin current
diminishes, the switching frequency drops, and the PSU output
rises. When the output reaches the voltage set-point, the
optocoupler will conduct, closing the loop and regulating the output.
Whenever the VCC pin is powered up, the DT/BF pin goes into
high impedance mode for 500 ms in order to sense the voltage
divider ratio and select the Burst Threshold. This setting is
stored until the next VCC recycle. The DT/BF pin then goes into
normal mode, resembling a diode to ground, and the sensed
current continuously sets the fMAX frequency. The burst threshold
frequencies are fixed fractions of fMAX. The internal oscillator
runs the internal counters at fMAX whenever the FEEDBACK pin
internal pull-up is on.
When a fault is detected on the IS, OV/UV, or VCC pin (UVLO),
the internal FEEDBACK pin pull-up transistor turns on for
131,072 clock cycles, to discharge the soft-start capacitor
completely, then a restart is attempted. The first power-up after
a VCC recycle only waits 1024 cycles, including the condition
where the OV/UV pin rises above the brown-in voltage for the
first time, after VCC is powered up.
Remote-Off
Remote-off can be invoked by pulling down the OV/UV pin to
ground, or by pulling up the IS pin to >0.9 V. Both will invoke a
131,072 cycle restart cycle. VCC can also be pulled down to
shut the device off, but when it is pulled up, the FEEDBACK pin
is pulled up to the VREF pin to discharge the soft-start capacitor
for only 1024 fMAX clock cycles. If this scheme is used, the
designer must ensure that the time the VCC is pulled down,
plus 1024 cycles, is sufficient to discharge the soft-start
capacitor, or if not, that the resulting lower starting frequency is
high enough so as not to cause excessive primary currents that
may cause the over-current protection to trip.
Current Sense
The IS pin senses the primary current. It resembles a reverse
diode to the GROUND pin. It is tolerant of negative voltages
provided the negative current is limited to <5 mA. Therefore it
must be connected to the current sense resistor (or primary
capacitive voltage divider + sense resistor) via a series current
limiting resistor of >220 Ω. Thus it can accept an AC waveform
and does not need a rectifier or peak detector circuit. If the IS
pin senses a nominal positive peak voltage of 0.5 V for 7
consecutive cycles, an auto-restart will be invoked. The IS pin
also has a second, higher threshold at nominally 0.9 V, which
will invoke an auto-restart with a single pulse. The minimum
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Rev. B 062011
LCS700-708
pulse width requirement for detection of both voltage thresholds
is nominally 30 ns. i.e. the thresholds have to be exceeded for
>30 ns for proper detection.
entering the two most sensitive pins on the list, namely the
FEEDBACK and DT/BF pins, will cause duty cycle, and deadtime imbalance, respectively.
Over-Temperature Shutdown
The HiperLCS has latching OTP. VCCH must be cycled to
resume operation once the unit drops down below the OTP
threshold.
Figure 5 and Figure 6 show two alternate schemes for routing
ground traces for optimum performance. Figure 5 shows a
layout footprint for the LCS with oval pads. These allow a trace
to be passed between pins 3 and 5, directly connecting the
ground systems for the bypass capacitors located on each side
of the IC.
Basic Layout Guidelines
The HiperLCS is a high-frequency power device and requires
careful attention to circuit board layout in order to achieve
maximum performance.
The bypass capacitors need to be positioned and laid out
carefully to minimize trace lengths to the pins they serve. SMD
components are recommended for minimum component and
trace stray inductance.
Table 2 describes the recommended bypass capacitor values
for pins that require filtering/bypassing. The table lists the pins
in the order of most to least sensitive. The bypass capacitor of
the pin at the top of the list being the most sensitive, receives
higher priority in bypass capacitor positioning to minimize trace
lengths, than the bypass capacitor of the pin below it. Noise
Figure 6 shows an LCS layout footprint with round pads that do
not allow traces to be routed between them due to insufficient
space. In this case, a jumper (JP1, a 1206 size 0 W resistor) is
used to connect the ground systems together and allow a
connection for pin 3 to be routed under JP1 to the optocoupler.
Transformer T1 is a source of both high di/dt signals and dv/dt
noise. The first can couple magnetically to sensitive circuitry,
while the second can inject noise via electrostatic coupling.
Electrostatic noise coupling can be reduced by grounding the
transformer core, but it is not economically feasible to reduce
the stray magnetic field around the transformer without drastically
reducing its efficiency. Sensitive traces and components (such
as the optocoupler) should be located away from the transformer
to avoid noise pickup.
Pin
Returned to Pin
Recommended Value
Notes
FEEDBACK (FB)
GROUND
4.7 nF (at 250 kHz)
Increase value proportionally for lower nominal frequency (e.g. 10
nF at 100 kHz). Forms a pole with FEEDBACK pin input
impedance which is part of feedback loop characteristic. Must
not introduce excessive phase shift at expected gain
crossover frequency. Noise entering FEEDBACK pin will cause
duty cycle imbalance.
DEAD-TIME/BURST
FREQUENCY (DT/BF)
GROUND
4.7 nF
Time constant of this capacitor and the source
impedance of the resistors connected to DT/BF pin
must be <100 µs. Noise entering DT/BF pin will cause
dead time imbalance.
CURRENT SENSE (IS)
GROUND
1 nF (at 250 kHz)
Value changes proportionally with nominal LLC stage
operating frequency. Forms an RC low pass filter with
recommended 220 W series resistor. Must not attenuate
AC signal of primary current sense.
VCC
GROUND
1 mF ceramic
VREF
GROUND
1 mF ceramic
VCCH
HB
0.1 mF - 0.47 mF
Bootstrap capacitor. Provides instantaneous current
for high-side driver for turning on high-side MOSFET.
Time constant formed with boost-strap current limiting
resistor (in series with bootstrap diode), delays VCCH
UVLO for a few switching cycles at start-up and during
burst mode operation for the first switching cycles
DRAIN
(DC Bus)
S1, S2
10-22 nF SMD ceramic
minimum, plus 22-100 nF
through-hole
Total of 22 nF per amp of nominal primary RMS current.
SMD part must be located directly at the IC and
connected close, with short traces. This prevents
ringing of D-S during hard-switching (loss of ZVS)
transients. It also reduces high-frequency EMI.
OV/UV
GROUND
4.7 nF
Table 2.
Bypass Capacitor Table in Order of Importance.
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LCS700-708
Figure 7 shows a an example of preferred routing for the
optocoupler and traces connected to the FEEDBACK pin. The
optocoupler is spaced away from the transformer, reducing
noise pickup. The optocoupler output trace (from pin 3) is also
routed to increase the distance between it and “active”
components and traces, such as T1 and the hot side of
capacitor C12. Resistor R20 is located close to U1 rather than
optocoupler U2, so that any noise picked up on the optocoupler
trace is filtered by the combination of R20 and C4 before it gets
to the FEEDBACK pin on U1. C4 is placed directly adjacent to
the FEEDBACK pin of U1 (pin 4).
VCCH is connected to the standby supply through a highvoltage ultrafast diode and a 2.2 W resistor connected in series.
This diode resistor network charges the VCCH bypass/storage
capacitor whenever the internal LLC low-side MOSFET is on.
The resistor limits the peak instantaneous charging current.
See R6 and D1 in Figure 8.
G Pin
Figure 5.
Placement of Bypass Capacitors on Signal Pins of IC.
Figure 6.
Alternate Layout for LCS Footprint using Round Pads with Jumper Connecting
Two Grounds Highlighted.
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Rev. B 062011
LCS700-708
Small Signal Bypass Capacitors
Please refer to Figure 5 Note the location of the small signal
bypass capacitors (highlighted) for the FEEDBACK, DT/BF, IS,
VREF, OV/UV and VCC pins, which allow short traces to their
pin connections and to the GROUND pin. Note that there is no
connection between the GROUND pin and the SOURCE pin or
the B- bus on the printed circuit board.
Figure 7.
VCCH Bypass Capacitor
Please refer to Figure 8. Note the location of the VCCH
capacitor (highlighted) which allows short connections to the
HB pin and the VCCH pin.
Drain to Source High-Voltage Bypass Capacitor
Please refer to Figure 9. Note the location of the B+ to B- highvoltage bypass capacitors (highlighted) placed at the IC, minimizing
the PCB trace length to the D and S pins.
Preferred Routing of Optocoupler and Traces to FEEDBACK Pin.
Figure 8.
Placement of VCCH Capacitor.
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Rev. B 062011
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LCS700-708
Bootstrap Circuit and HB Node Layout
Please refer to Figure 10. Note the location of the bootstrap diode,
capacitor, resistor, and the HB trace routing. The objective is to
keep them away from the small signal components and traces,
such as the feedback optocoupler. Do not unnecessarily
increase the area of the PCB traces on this node, because it will
increase the dv/dt (capacitive) coupling to low-voltage circuits.
Heat Sink Grounding
The exposed metal in the back of the HiperLCS package is
internally connected to the GROUND pin. If the HiperLCS has a
dedicated heat sink and there is no electrical insulator between
the device and the heat sink, the heat sink should be floating and
not electrically connected anywhere else. If the heat sink is
shared with other devices in the system, and the heat sink
requires grounding to minimize EMI, a thin insulator is strongly
recommended under the HiperLCS, for improved noise, surge,
and system-level ESD immunity. The resulting increase in thermal
resistance must be considered in the thermal design.
Transformer Secondary
The transformer secondary pins, output diodes, and main output
capacitors should be positioned close together and routed with
short thick traces. This is critical for secondary current symmetry
and to minimize output diode inverse voltage stress. The use of
ceramic capacitors allows placement between the transformer
secondary pins and the output rectifier, producing a very tight
layout. See Figure 11. The secondary winding halves should be
inter-twined together before they are wound on the bobbin. This
minimizes the leakage inductance between them and greatly
improves current symmetry and minimizes output diode inverse
voltage stress. For a 2-output design the half-windings of a given
output need to be intertwined.
DRAIN
SOURCE
Figure 9.
Placement of B+ and B- High-Voltage Bypass Capacitors.
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Rev. B 062011
LCS700-708
Transformer
Primary
High-Side
Figure 10. Placement of Boot Strap Diode, Capacitor, Resistor and the High-Voltage Trace Routing.
Secondary
Output Rectifier
Capacitors
Center
Tap
Secondary
Figure 11. Placement of Capacitors Between Transformer Secondary Pins and
the Output Rectifier to minimize and Equalize Loop Areas.
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LCS700-708
Key Design Details
The LLC converter is a variable frequency resonant converter.
As input voltage decreases, the frequency must decrease in
order to maintain output regulation. To a lesser extent, as load
reduces the frequency must increase. When the converter is
operating at the series resonant frequency, the frequency changes
very little with load. The minimum operating frequency required
occurs at brownout (minimum input voltage), at full load.
Operating Frequency Selection
For lowest cost, and smallest transformer size with the least
amount of copper, the recommended nominal operating frequency
is ~250 kHz. This allows the use of low-cost ceramic output
capacitors in place of electrolytic capacitors, especially at
higher output voltages (≥12 V). If the core and bobbin used
exhibits too much leakage inductance for 250 kHz, operation at
180 kHz also results in excellent performance. For optimal
efficiency at 250 kHz, AWG #44 (0.05 mm) Litz is recommended
for the primary, and AWG #42 (0.07 mm) for the secondary
winding. Thicker gauge lower cost Litz can be used at the
expense of increased copper loss and lower efficiency. Litz
gauge (AWG #38 or 0.1 mm) is optimal for very low frequencies
(60-70 kHz), requires much larger transformers and greater
lengths of Litz wire.
For nominal operating frequencies even as low as 130 kHz, the
use of PC44 or equivalent core material is recommended for
reduced losses. For a given transformer design, shifting the
frequency up (by substituting a smaller resonant capacitor), will
reduce core loss (due to reduced AC flux density BAC) and
increase copper loss. Core loss is a stronger function of flux
density than of frequency. The increased frequency increases
copper loss due to eddy current losses.
Nominal operating frequencies >300 kHz start to lose significant
efficiency due to increased eddy current losses in the copper,
and due to the fact that a more significant percentage of time is
spent on the primary slew time (ZVS transition time) which
erodes the percentage of time that power is transferred to the
secondary.
Resonant Tank and Transformer Design
Please refer to the Application Note AN-55 for guidance on
using the PIXls HiperLCS spreadsheet which assists in the
entire design process.
Primary Inductance
The optimal powertrain design for the HiperLCS uses a primary
inductance that results in minimal loss of ZVS at any steadystate condition. Some loss of ZVS during non-steady-state
conditions is acceptable. Reducing primary inductance
produces higher magnetizing current which increases the range
of ZVS operation, but the increased magnetizing current
increases losses and reduces efficiency.
The calculation of the primary inductance to be used for a
first-pass design is based on device size, rated load, minimum
input voltage, and desired operating frequency. It is provided in
the PIXls spreadsheet. LPRI is the primary inductance of an
integrated transformer (high leakage inductance), or in the case
of the use of an external series inductance, the sum of this
inductance and the transformer primary inductance.
Leakage Inductance
The parameter KRATIO is a function of leakage inductance:
K RATIO = L PRI - 1
L RES
The recommended KRATIO is from 2.5 - 7. This determines the
acceptable range of leakage inductance.
LRES is the leakage inductance in an integrated transformer; if a
separate series inductor is used, it is the sum of this inductance
and the leakage inductance of the transformer.
A low KRATIO (high leakage inductance) may not be capable of
regulation at the minimum input voltage, and may show
increased transformer copper losses due to the leakage flux. A
high KRATIO (low leakage inductance) will have high peak and
RMS currents at low-line, and require a lower primary inductance
to achieve ZVS operation over a suitably wide range, which
increases the resonant circulating current, reducing efficiency.
The core and bobbin designs available to the designer may limit
the adjustability of leakage inductance. Fortunately, excellent
performance can be achieved over a relatively wide range of
leakage inductance values.
The KRATIO directly affects the frequency range that the LLC needs
to operate in order to maintain regulation over the input voltage
range. Increasing KRATIO increases this frequency range,
lowering fMIN.
A low fMIN is only a potential problem for low frequency designs
which typically run at higher nominal BAC. This may allow the
core to reach saturation when operating at fMIN. Operating at
fMIN occurs when the input voltage is at a minimal (input
brown-out).
For a design with a separate resonant inductor, running the
inductance on the low side of the range (KRATIO = 7), minimizes
the size and cost of the inductor.
Adjusting Leakage Inductance
Sectioned bobbins (separated primary and secondary) are
commonly used for LLC converters. Increasing or decreasing
both primary and secondary turns (while maintaining turns ratio)
will change the leakage inductance proportionally to the square
of primary turns.
If the leakage inductance is too high, one possible solution is to
use a 3-section bobbin, where the secondary is in the middle
section, and the primary winding is split into 2 halves connected
in series.
Lastly, if the leakage inductance is too low an external inductor
may be added.
11
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Rev. B 062011
LCS700-708
Resonant Frequency
The series resonant frequency is a function of LRES and CRES, the
resonant capacitor. For any given value of LRES, the value of
CRES can be adjusted for the desired series resonant frequency
fRES. For best efficiency the resonant frequency is set close to
the target operating frequency at nominal input voltage.
Operating Frequency and Frequency Ratio
The operating to resonant frequency ratio fRATIO is defined as:
fRATIO =
fSW
fRES
fRATIO = 1 signifies the converter is operating at the series
resonant frequency.
The main determinant of fRATIO is the transformer turns ratio.
Increasing primary turns lowers fRATIO for a given input and
output voltage.
The recommended fRATIO at nominal input voltage is 0.92 – 0.97.
Operating at resonance often yields the highest efficiency for
the resonant powertrain if output rectifier selection is ignored.
However, operating slightly below resonance (which puts the
rectifiers in discontinuous conduction mode), allows the use of
lower voltage diodes or synchronous MOSFETs, which have
lower losses, increasing overall efficiency. This is because at
high-line, when the converter needs to operate above resonance,
the rectifiers operate less deeply in continuous mode, reducing
the magnitude of their current commutation, reducing their stray
inductance voltage spikes. (The stray inductance is comprised
of the leakage inductance between secondary phases and the
stray inductance in the connections to the rectifiers and output
capacitors).
Conversely, operating at a very low fRATIO (<0.8) results in higher
RMS and peak currents. In some cases, this may result in an
optimal design because it allows the use of lower voltage rating,
lower VF rectifier as they do not operate in continuous conduction
mode even at high-line, results in no voltage spikes enabling a
lower voltage rating.
An LLC half-bridge converter will operate at resonance when
this equation is true:
VIN
2
VOUT
= n EQ
Where nEQ is the transformer equivalent circuit turns ratio. Note
that the nEQ of an integrated transformer is lower than its
physical turns ratio NPRI / NSEC. The secondary turns is that of
each half-secondary. VOUT in the above equation is equal to
output voltage + diode drop. The divisor “2” is due to the
half-bridge configuration – each half-cycle conducts half the
input voltage to each secondary half.
Note that if the resonant capacitor or inductance value is
changed, both switching frequency and resonant frequency
change, but fRATIO changes little.
For a given design, the input voltage at which the LLC operates
at resonance is VINPUT(RESONANCE). Below this voltage, the LLC
operates at a lower frequency (below resonance). Thus for the
recommended fRATIO ≈ 0.95 at nominal input voltage, VINPUT(RESONANCE)
will be slightly higher than the nominal voltage.
For a design with a variable nominal input voltage (e.g. no PFC
pre-regulator), it is recommended that the initial turns ratio be set
so that VINPUT(RESONANCE) is at about halfway between maximum and
minimum input voltage. For a design with a variable output voltage
(e.g. constant current regulated output), it is recommended that
the initial turns ratio be set to operate the LLC at resonance at a
point halfway between minimum and maximum output voltages.
Dead-Time Selection
The vast majority of designs using HiperLCS, regardless of power
and operating frequency, work very well with a dead-time of
between 290 and 360 ns. Designs that require a low VBROWNOUT
tend to require shorter dead-times.
The dead-time setting is a compromise between low-line / full
load (low frequency), and minimum-load / high-line (highfrequency) conditions. Low-line / full load operation has short
optimal dead-times, while minimum load / high-line has long
optimal dead-times.
A dead-time setting that is longer than optimal for low-line / full
load operation, exhibiting partial loss of ZVS, is acceptable if the
condition does not occur during steady-state operation – i.e.
appears only during transient conditions, such as hold-up time.
Operation with loss of ZVS during steady-state operation leads
to high internal power dissipation and should be avoided.
A dead-time setting that is shorter than optimal for high-line /
minimum-load operation, will tend to cause the feedback sign
to invert and force the HiperLCS to enter burst mode. This is
acceptable if the resulting burst mode operation is acceptable
(i.e. repetition rate does not produce audible noise and if the
large signal transients, wherein the HiperLCS enters and exits
burst mode, is acceptable). Note that with a PFC pre-regulated
front end, a load dump (e.g. 100% to 1% load step) will exhibit a
transient input voltage condition only temporarily (e.g. Input
voltage to LLC stage will increase from 380 V to 410 V and
relatively slowly return to 380 V). Note also that the Burst
Threshold frequency setting is another variable available to the
designer to tune burst mode.
OV/UV Pin
The HiperLCS OV/UV pin which monitors the input (B+) voltage,
has a brown-out shutdown threshold (VSD(L)) of nominally 79% of
the brown-in (turn-on) threshold (VSD(H)), which in turn, is nominally
2.4 V. The overvoltage (OV) lockout shutdown threshold (VOV(H))
is nominally 131% of the brown-in start-up threshold, and the
OV restart point (VOV(L)) at nominally 126%. The ratios of these
thresholds are fixed and selected for maximum utility in a design
with a PFC pre-regulator front-end with a fixed output voltage
set-point. The resistor divider ratio has to be selected so that
brown-in point is always below the PFC output set-point, and
so that the OV restart (lower) threshold, is always above it,
including component tolerances.
During hold-up time, the voltage will drop from the nominal
value, down to the brown-out threshold, whereby the HiperLCS
will stop switching.
12
Rev. B 062011
www.powerint.com
LCS700-708
OV/UV pin resistor divider chosen
for minimum hold-up capacitance
OV/UV pin resistor divider chosen
for minimum required LLC gain
495 V
385 V
376 V
VOVH
475 V
VOVL
436 V
VOVH
418 V
385 V
VSDH
331 V
298 V
VSDH
VSDL
200 V
262 V
Time
VOVL
VSDL
200 V
Time
PI-6154-051811
Figure 14. OV/UV Pin Voltage Thresholds, at Minimum and Maximum Divider Ratios, for 385 V Nominal Input Voltage.
If the input voltage is variable (e.g. no PFC pre-regulator), and
the variation is greater than 24%, the OV threshold should be
increased with external circuitry on the resistor divider. External
circuitry is also needed if VBROWNOUT needs to be reduced below
the default ratio.
VREF
RFMAX
In the example in the left-hand side of Figure 14 the resistor
divider is set so that brown-in threshold is 376 V, just under the VPFC
set-point of 385 V. The OV shutdown threshold is 495 V, which
gives adequate margin against the device max VDS rating of 530 V.
This minimizes required minimum LLC gain, and minimizes the
peak current at brown-out. In the example on the right of Figure
14, the OV restart threshold is set to 418 V, just above VPFC. This
maximizes hold-up time for a given bulk capacitor value.
The OV/UV pin has an integrated 5 MW pull-down to detect
pin-open fault conditions.
The recommended pull-down resistor value for the OV/UV pin
divider is 20 kW - 22 kW. A very large resistor value will cause
the pin pull-down current to affect accuracy, and a small value
will increase power loss.
DT/BF Pin
The DT/BF pin senses the voltage divider ratio by entering into a
high-impedance mode for 500 µs after VCC is applied. It
senses the pin voltage, before the HiperLCS starts switching.
See Figure 15.
There are 3 discrete Burst Threshold settings that can be
selected. (This determines the burst start and stop switching
frequencies, see Table 3).
For proper selection, set the ratio of RBURST to RFMAX as per Table 3.
Table 3.
DT/BF
RBURST
GND
PI-6460-051811
Figure 15.
DT/BF Pin Divider.
After the Burst Threshold detection, the DT/BF pin operates in
normal mode, sinking current, resembling a diode to ground,
with a Thevenin equivalent circuit of nominally 0.66 V and
1.1 kΩ. The current from the resistor divider into the pin,
determines the dead-time and the maximum frequency fMAX.
The relationship between dead-time and fMAX is fixed and
approximated by:
fMAX ^kHz h =
270000
Dead - Time ^nsh
The relationship between DT/BF pin current and fMAX, and
switching frequency vs. FEEDBACK pin current (which has the
same characteristic), is show in Figure 16.
The burst mode start and stop frequency thresholds are fixed
fractions of fMAX, which depend on the Burst Threshold setting,
as set by the resistor divider ratio on the DT/BF pin.
Burst Threshold
RBURST / RFMAX
1
19
Burst Threshold
Setting
fSTART/fMAX
fSTOP/fMAX
2
9
1
7/16
8/16
3
5.67
2
6/16
7/16
3
5/16
6/16
Burst Threshold Selection Table.
The Burst Threshold setting is stored until VCC is powered down.
Table 4. Burst Start and Stop Frequencies as Ratios of fMAX.
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Rev. B 062011
400
Current (μA)
300
250
200
400
350
300
150
250
100
200
50
150
0
0
200
400
600
Frequency (kHz)
800
fMAX is the frequency at which the internal counters run when the
HiperLCS is in the off-state of the auto-restart cycle, or in the
power-up delay before switching.
The minimum recommended dead-time is 275 ns, and thus the
maximum fMAX setting is 1 MHz.
To simplify the selection of RFMAX, see the selection curves in Figure 17.
PI-6458-051911
BT1
BT2
BT3
11.0
10.0
9.0
8.0
7.0
6.0
5.0
250
300
350
400
450
Dead-Time (ns)
Figure 17. RFMAX vs. Dead-Time, for the 3 Different Burst Threshold Settings.
300
350
400
450
Dead-Time (ns)
500
The fSTOP to fSTART ratio is fixed, and dependent on the Burst
Threshold setting (see Table 5).
Burst Threshold
Setting
fSTOP / fSTART
1
1.14
2
1.17
3
1.20
Table 5. Ratio of fSTOP /fSTART vs. Burst Threshold Selection.
As a first approximation, during burst mode, the frequency
ramps from fSTART to fSTOP; then switching stops, and then the cycle
repeats.
FEEDBACK Pin
The FEEDBACK pin is the voltage regulation FEEDBACK pin. It
has a nominal Thevenin equivalent circuit of 0.65 V and 2.5 kΩ.
In normal operation, it sinks current. During the off-period of
auto-restart, and during the clocked delay before start-up, it pulls
up internally to VREF in order to discharge the soft-start capacitor.
The current entering the pin determines switching frequency.
Higher current yields higher frequency and thus reduces LLC
output voltage. In a typical application an optocoupler connected
to the VREF pin pulls up on the FEEDBACK pin, via a resistor
network. The optocoupler is configured to source increasing
FEEDBACK pin current, as the output rises. The resistor network
between the optocoupler, FEEDBACK pin, and VREF pin,
determine the minimum and maximum FEEDBACK pin current
(and thus the minimum and maximum operating frequency), that
the optocoupler can command as it goes from cutoff to saturation.
This network also contains the soft-start timing capacitor, CSTART
(Figure 19).
The minimum frequency as set by this network must be lower
than the frequency required by the powertrain at minimum input
voltage. In Figure 19 this is determined by the sum of RFMIN and
RSTART. The FEEDBACK pin current is determined by these two
resistors when the optocoupler is cut off. CSTART can be ignored
during normal operation. Do not confuse RSTART, which determines
14
Rev. B 062011
500
Figure 18. fSTART (Lower Burst Threshold Frequency) vs. Dead-Time Setting for
Different Burst Threshold Settings (BT1, BT2, BT3).
For example, if BT2 is selected, and fMAX is 800 kHz, then fSTART
= 300 kHz, and fSTOP = 350 kHz. If during normal operation the
load is reduced and the frequency rises to 350 kHz, the switching
will stop. This causes the output voltage to drop and the
feedback loop to decrease the FEEDBACK pin current. When
the current decreases to a value which corresponds to 300 kHz,
switching will commence, and the cycle will repeat. During
start-up mode, however, the outputs can switch at a frequency
between fSTOP and fMAX (250 kHz and 800 kHz in the above
example). Start-up mode is exited once the switching frequency
drops below fSTOP, and the HiperLCS will subsequently enter
burst mode if the feedback loop attempts to produce a
switching frequency >fSTOP.
12.0
250
1000
Figure 16. FEEDBACK Pin and DT/BF Pin Current vs. Frequency.
13.0
BT1
BT2
BT3
450
fSTART (kHz)
350
RFMAX (kΩ)
500
PI-6150-052011
450
PI-6457-051911
LCS700-708
www.powerint.com
Bursting Duty ≈ 50%
10 μs / div
3.4 V
VREF
CSTART
RFMIN
RSTART
U1B
D1
FB
CFB
4.7 nF
IPRI
VHB
PI-6463-060711
LCS700-708
850 ns / div
ROPTO
RLOAD
GND
~850 kHz
PI-6118-051711
Severe Loss of ZVS
Figure 20. Bursting at fMAX Causes High Internal Dissipation Due to Loss of
ZVS and Should be Avoided.
Figure 19. Feedback Network Shown with Additional Load Resistor.
start-up frequency, and fSTART, which is the burst mode start
(lower) threshold frequency.
Resistor RLOAD provides a load on the optocoupler, and speeds
up the large signal transient response during burst mode. The
recommended value is ~4.7 kΩ. Diode D1 prevents RLOAD from
loading RFMIN when the optocoupler is cut off. Diode D1 can be
omitted and a combination of resistor values found to achieve the
desired fMIN but the resulting tolerances will be poor. Resistor
ROPTO will improve the ESD and surge immunity of the PSU. It
also improves burst mode output ripple voltage. Its maximum
value must be such that the FEEDBACK pin current is equal to
the DT/BF pin current when the optocoupler is in saturation and
the FEEDBACK pin is at 2.0 V (please see PIXls HiperLCS
spreadsheet). This is to ensure that if the HiperLCS does not exit
start-up mode, because the feedback loop did not allow the
switching frequency to drop below fSTOP, then it can regulate at
light load by bursting at fMAX. Note however bursting at fMAX can
lead to high internal dissipation due to loss of ZVS and should be
avoided. See Figure 20.
Capacitor CSTART should be sized at the minimum possible value
that exhibits a 7 consecutive-cycle peak current at start-up that is
just below the peak current measured at brown-out and full load.
A larger value will slow down start-up and will make it more likely
that fSTOP is not reached. This can prevent exiting start-up mode
when the HiperLCS is powered up at high-line and minimum load,
and may subsequently cause the HiperLCS to burst at fMAX
instead of between fSTART and fSTOP.
PI-6151-060911
100
RFB (kΩ)
The FEEDBACK pin current at start-up is determined by the value
of RSTART because the voltage on CSTART will be zero. For minimum
start-up peak currents, this current should match or slightly
exceed the DT/BF pin current so that start-up switching frequency
begins at fMAX. The resulting value of RSTART will be approximately
10% lower than the value of the pull-up resistor on the DT/BF pin.
The frequency will slide down as CSTART charges. If RSTART is
smaller than that which provides start-up at fMAX, it will create an
additional delay before start-up switching. Please see the PIXls
HiperLCS spreadsheet.
300
50
20
10
4
20
50
100
200
500
1000
Frequency (kHz)
Figure 21. VREF to FB External Resistance vs. Frequency.
In order to calculate RFMIN and RSTART, use the following equation
which describes nominal resistance from FEEDBACK pin to
VREF pin, vs. frequency:
R FB =
3574
f ^0.6041 + 0.1193 # LOG^ f hh
Where RFB is in kΩ and f is in kHz.
To calculate the minimum RSTART, which produces start-up at fMAX,
use the above equation with f = fMAX from the equation relating
dead-time and fMAX.
To set fMIN, use the above equation with f = fMIN × 0.93. Where
0.93 is to ensure that, despite the worst case frequency tolerance
of -7%, the frequency can go below fMIN, guaranteeing regulation
at VBROWNOUT.
Using the resulting calculated value for RFB, calculate RFMIN:
R FMIN = R FB - R START
The sum of RFMIN and RSTART determines fMIN.
15
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Rev. B 062011
LCS700-708
Start-Up and Auto-Restart
At start-up and during the off-state of the auto-restart cycle, the
FEEDBACK pin is internally pulled up to the VREF pin. This
keeps the output MOSFETs off and discharges the soft-start
capacitor, in preparation for soft-start.
At start-up, this state remains for 1024 clock cycles at frequency
fMAX. During the off-state of auto-restart, or if the OV/UV or IS pin
is triggered while the VCC remains above its UVLO threshold, this
state remains for 131,072 clock cycles.
After 1024 or 131,072 cycles (as the case may be), the HiperLCS
turns off the internal pull-up transistor, the soft-start capacitor
begins to charge, the output MOSFETs switch at fMAX, current in
the FEEDBACK pin diminishes, the frequency begins to drop,
and the PSU output rises.
PI-6471-052411
6
A
4
B
80
70
Primary Current
0
50
-2
40
-4
30
-6
Volts (V)
60
2
Amps (A)
It should be noted that the 4.7 nF decoupling capacitor, CFB
(see Figure 19), in conjunction with the 2.5 kΩ input resistance
presented by the FEEDBACK pin, form a pole in the LLC
transfer function. This can add significant phase lag to the
feedback loop. A typical value for a 250 kHz design with a
3 kHz crossover frequency is 4.7 nF. To prevent loop instability,
the value of the 4.7 nF capacitor should not be increased
arbitrarily. At the other extreme, insufficient FEEDBACK pin
bypass capacitance or poor layout may cause duty cycle
asymmetry.
20
Output Voltage
10
-8
0
-10
0
0.5
1
1.5
2
2.5
3
3.5
Time (ms)
4
4.5
5
Figure 22. Typical Start-up Waveform. Observe Initial Current Spike ‘A’ to Ensure
it is Below the 1-Cycle Current Limit. A Higher fMAX Reduces it. Size
the Soft-Start Capacitor so that the Peak of ‘B’ is just Below the Peak
Current at VBROWNOUT at Full Load.
The FEEDBACK pin has a current limit equal to the current
flowing into the DT/BF pin. This limits the maximum current that
charges the soft-start capacitor at start-up. If RSTART is smaller
than that which allows the FEEDBACK pin current to match the
DT/BF pin current at start-up, an additional delay is introduced.
CSTART will charge at the current limit, and switching will only
commence when the FEEDBACK pin voltage drops below 2.0 V.
Thus the designer can add an additional start-up delay if desired.
IS Pin
The IS pin has 2 thresholds: nominally 0.5 V and 0.9 V. The IS
pin can tolerate small negative voltages and currents, and thus
does not need a peak detector or rectifier circuit. The pin has a
reverse-biased diode to ground equivalent circuit, and can
tolerate a maximum negative current of 5 mA. The primary
current is sampled by a primary, B- referenced current sense
resistor, or by a capacitor current divider + current sense resistor
combination circuit. In order to limit the negative current to 5 mA,
a current limiting resistor between the sense resistor and the IS
pin is necessary, with a minimum value of 220 Ω. Using the
minimum value maximizes the IS pin bypass capacitor value
and thus pin noise rejection, for a given RC pole frequency.
The IS pin will invoke a restart if it sees 7 consecutive pulses
>0.5 V. It will also invoke a restart if a single pulse exceeds 0.9 V.
The minimum pulse detection time is nominally 30 ns – i.e. the
pulses must be higher than the threshold voltage for >30 ns.
As the soft-start capacitor continues to charge, the current
through RSTART and thus the FEEDBACK pin decreases, reducing
switching frequency. The output voltage climbs; and when the
feedback loop closes, the optocoupler conducts and starts
controlling the switching frequency thus the output voltage.
The “capacitive divider” circuit in Figure 23 reduces power
dissipation and improves efficiency over a simple current sense
resistor circuit. The two capacitors, main resonant capacitor
C11, and sense capacitor C12, form a current divider. The
portion of the primary current routed through C12 is
For example, for fMAX = 800 kHz, the start-up delay after VCC
power-up is 1.3 ms. If IS, or the OV/UV pin are tripped, autorestart is invoked, with a restart delay of 164 ms.
Remote-Off
Remote-off can be invoked by pulling down the OV/UV pin to
ground, or by pulling up the IS pin to >0.9 V. Both will invoke a
131,072 cycle restart cycle. VCC can also be pulled down to shut
the device off, but when it is pulled up, the FEEDBACK pin is
pulled up to the VREF pin to discharge the soft-start capacitor for
only 1024 fMAX clock cycles. If this scheme is used, the designer
must ensure that the time the VCC is pulled down, plus 1024
cycles, is sufficient to discharge the soft-start capacitor, or if not,
that the resulting lower starting frequency is high enough so as
not to cause excessive primary currents that may cause the
over-current protection to trip.
C12
.
C11 + C12
Consequently, the voltage at the IS pin is equal to
IP #
C12
C11 + C12
#
R11,
where IP is the primary current flowing from the HB pin through
the transformer primary. The current in the sense capacitor
passes through sense resistor R11. Resistor R11 is the main
means for tuning current limit. The signal on R11, an AC
voltage, passes through low-pass filter R12 and C7, to the IS
pin. Note that R11 is returned to the GROUND pin and not to
SOURCE pin.
16
Rev. B 062011
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LCS700-708
24.0
400
23.9
300
200
100
0
0
LLC
Transformer
25
Time (μs)
50
Figure 25. Zoom in of First Few Switching Cycles of Burst Pulse Train of Figure 24.
The First 2 Cycles Show That the High-Side Driver has not Turned
on yet. The Switching Frequency of the First Few Cycles is fSTART,
335 kHz in This Case. The Ringing on the Output is from the
Output Filter.
HB Pin
C12
47 pF
1 kV
C11
6.8 nF
1 kV
IS Pin
GROUND
Pin
24.1
HB Voltage (V)
Burst Mode Operation and Tuning
Burst mode will produce a typical waveform such as in Figure 24.
During the burst pulse train, the switching frequency rises from
fSTART to fSTOP.
PI-6469-062811
Output Ripple Voltage (V)
The recommended series resistor value of 220 W and the bypass
capacitor form a low-pass filter, and its time constant must not
cause significant attenuation of the current sense signal at the
nominal operating frequency. The effect of the attenuation is
greatest for the first pulse in the start-up current waveform, and
can also affect proper shutdown during short-circuit testing,
which typically trips the 7-cycle current limit. Place a closecoupled probe across the IS pin bypass capacitor and compare
the waveform to the primary current.
C7
1 nF
R12
220 Ω
R11
24 Ω
S Pin
PI-6161-051711
Figure 23. Capacitive Divider Current Sense Circuit.
I = C # dv
dt
PI-6468-062811
Where I = load current. C is the total output capacitance.
24.1
Output Ripple Voltage (V)
HB Voltage (V)
24.0
23.9
400
300
200
100
0
Burst Repetition Rate
0
50
Time (ms)
If the initial output ripple spike at the beginning of the burst
pulse train is ignored, the output ripple somewhat resembles a
sawtooth. See the output ripple waveform in Figure 24. When
the HiperLCS is switching, the output rises. When it stops
switching, the output falls. The top of the sawtooth is where the
burst pulse train ends, because the feedback loop has commanded
a frequency = fSTOP. The bottom of the sawtooth is where the
burst pulse train begins, because the feedback loop has
commanded a frequency = fSTART. As such, the burst mode
control resembles a hysteretic controller, where the top and
bottom of the sawtooth are fixed by the feedback loop gain.
The downward slope of the sawtooth is merely the output
capacitors discharging into the load, with dv/dt:
100
Figure 24. Typical Waveform of Burst Mode. 24 V / 150 W HiperLCS Design at
Zero Load. The Initial Spike (circled) Size is Dependent on Post-Filter
Electrolytic Capacitor ESR.
The upward slope of the sawtooth is dependent on the difference
between the current delivered by the powertrain, and the current
drawn by the load. For a given design, the upward slope
increases with input voltage.
The burst repetition rate (frequency) then increases with load.
When the load reaches a point where the powertrain can
regulate at a frequency <fSTOP, the bursting will stop. When the
load current decreases (from heavy load), frequency increases,
and when it reaches fSTOP, bursting will commence.
In a typical design, fSTART must be chosen to be at least 20-40%
higher than the nominal switching frequency. Figure 18 shows
the relationship between fSTART and dead-time, and Table 5 the
ratio of fSTOP to fSTART vs. Burst Threshold setting number). In
some cases the designer may choose to change dead-time
slightly in order to change fSTART and fSTOP. Some designs may
only enter burst mode at zero load and an input voltage above
nominal.
17
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Rev. B 062011
LCS700-708
PI-6470-062811
24.1
Output Ripple Voltage (V)
HB Voltage (V)
24.0
400
23.9
300
200
100
Higher fSTART will decrease the load threshold at which bursting
begins, increase the input voltage threshold and decrease the
output ripple in burst mode, but will increase the burst repetition
rate, which may introduce audible noise in some combinations
of line and load. The choice of fSTART will affect the large signal
transient response where the HiperLCS goes in and out of burst
mode.
0
-5
0
50
Time (μs)
100
Figure 26. Zoom in of Last Few Switching Cycles of Burst Pulse Train of Figure 24.
The Switching Frequency of the Last Few Cycles is fSTOP, 383 kHz in
This Case (arrow). The Ringing in VHB After Switching Stops, is the
Primary Inductance Ringing with the MOSFET Capacitance.
18
Rev. B 062011
www.powerint.com
LCS700-708
Absolute Maximum Ratings
Instantaneous Repetitive D or HB Current(5)...............................
................................... VCC, VCCH = 11.5 V, 25 °C.
LCS700......................................................... 5.2 A
LCS701..........................................................7.7 A
LCS702....................................................... 10.3 A
LCS703.................................................. 12.9 A
LCS705....................................................... 19.3 A
LCS708....................................................... 30.9 A
Instantaneous Repetitive D or HB Current(5)................................
....................... VCC, VCCH = 11.5 V, 125 °C
LCS700......................................................... 4.2 A
LCS701......................................................... 6.2 A
LCS702......................................................... 8.3 A
LCS703.................................................. 10.4 A
LCS705....................................................... 15.6 A
LCS708........................................................ 24.9 A
DRAIN Pin Voltage D(1)..........................................-1.3 V to 530 V
Half-bridge Voltage, HB(1)............................... -1.3 V to D + 0.5 V
Half-bridge Voltage Slew Rate, HB ..................................... 10 V/ns
SUPPLY Pin Voltage, VCC(1), VCCH(2).........................-0.3 V to 15 V
G Pin Voltage(1)..................................................... -0.3 V to 0.3 V
IS Pin Voltage(3) ............................................. -0.65 to VREF + 0.3 V
DT/BF and FEEDBACK Pin Voltages(3)........ -0.3 to VREF + 0.3 V
OV/UV Pin Voltage(3).....................................-0.3 to VCC + 0.3 V
Pin Current (VREF, OV/UV, DT/BF, FEEDBACK, IS).........±100 mA
Junction Temperature.......................................-40 °C to 150 °C
Storage Temperature....................................... -65 °C to 150 °C
Lead Temperature(4)..........................................................260 °C
ESD Rating (JESD22-A114-B, HBM).....................................2 kV
Notes:
1. Voltage referenced to S.
2. Voltage referenced to HB.
3. Voltage referenced to G.
4. 1/16 inch from case for 5 seconds.
5. One-cycle peak current can exceed repetitive maximum current
for t < 460 ns if TJ < 100 °C and drain voltage ≤ 400 VDC.
Thermal Resistance
Junction to Case Thermal Resistance(1,3):
LCS700 (qJC)............................................. 7.6 °C/W
LCS701 (qJC)............................................ 7.0 °C/W
LCS702 (qJC)...........................................6.6 °C/W
LCS703 (qJC).......................................6.2 °C/W
LCS705 (qJC)............................................5.9 °C/W
LCS708 (qJC)............................................5.5 °C/W
Junction to heat sink Thermal Resistance(1,2):
LCS700 (qJH).......................................... 10.1 °C/W
LCS701 (qJH).............................................9.5 °C/W
LCS702 (qJH)............................................ 9.1 °C/W
LCS703 (qJH)............................................8.7 °C/W
LCS705 (qJH)............................................8.4 °C/W
LCS708 (qJH)............................................8.0 °C/W
Hottest Junction to OT Sensor Thermal Offset(1,2,4):
LCS700 (ΔTJ-OT ).........................................4.6 °C/W
LCS701 (ΔTJ-OT )........................................4.0 °C/W
Parameter
Symbol
LCS702 (ΔTJ-OT )........................................3.5 °C/W
LCS703 (ΔTJ-OT )...................................3.2 °C/W
LCS705 (ΔTJ-OT )........................................2.8 °C/W
LCS708 (ΔTJ-OT )........................................2.5 °C/W
Notes:
1. Both power switches each dissipating half the total power.
2. Mounted to an aluminum heat sink with uniform coverage of
Thermalloy thermal paste. Mounting clip with normal force
>30 N applied to the center of the package.
3. Junction to case thermal resistance is based on hottest
junction, case temperature measured at center of package
back surface.
4. Temperature difference between hottest junction and overtemperature sensor.
5. Thermal resistance values are preliminary and subject to change.
Conditions
SOURCE = 0 V; TJ = 0 to 100 °C
Typ
Max
LCS700
LCS701
LCS702
LCS703
LCS705
LCS708
LCS700, I = 0.8 A
LCS701, I = 1.2 A
LCS702, I = 1.6 A
LSC703, I = 2.0 A
LCS705, I = 3.0 A
1.53
1.00
0.74
0.60
0.40
60
60
65
80
120
200
1.82
1.24
0.92
0.73
0.49
LCS708, I = 4.8 A
0.26
0.31
VCC = 12 V, VCCH = 12 V
Min
Units
(Unless Otherwise Specified)
Half-Bridge
OFF-State Current
ON-State Resistance
IDSS
RDS(ON)
Measured from D to
HB or from HB to S
TJ = 100 °C, VCC =
12 V, VCCH = 12 V,
VD = 424 V
Measured from D to
HB or from HB to S
VCC = 12 V, VCCH =
12 V, TJ = 25 °C
mA
W
19
www.powerint.com
Rev. B 062011
LCS700-708
Parameter
Symbol
Conditions
SOURCE = 0 V; TJ = 0 to 100 °C
Typ
Max
Units
LCS700, I = 0.8 A
LCS701, I = 1.2 A
LCS702, I = 1.6 A
LCS703, I = 2.0 A
LCS705, I = 3.0 A
LCS708, I = 4.8 A
LCS700
LCS701
LCS702
LCS703
LCS705
2.15
1.42
1.05
0.85
0.58
0.36
134
201
268
335
503
2.63
1.78
1.33
1.06
0.71
0.45
W
LCS708
LCS700, I = 0.8 A
LCS701, I = 1.2 A
LCS702, I = 1.6 A
LSC703, I = 2.0 A
LCS705, I = 3.0 A
804
1.15
1.15
1.15
1.15
1.15
LCS708, I = 4.8 A
1.15
VCC = 12 V, VCCH = 12 V
Min
(Unless Otherwise Specified)
Half-Bridge (cont.)
ON-State Resistance
Half-Bridge
Capacitance
Diode Forward
Voltage
RDS(ON)
Measured from D to
HB or from HB to S
VCC = 12 V, VCCH =
12 V, TJ = 100 °C
CHB
Effective half-bridge
capacitance.
VHB swinging from
0 V to 400 V or
400 V to 0 V,
See Note A
VFWD
Measured from HB
to D or from S to HB
TJ = 125 °C
pF
V
Power Supply
VCC Supply
Voltage Range
VCC
See Note C
11.4
12
15
V
VCCH Supply
Voltage Range
VCCH
See Note C
11.4
12
15
V
Start-Up Current
ICC(OFF)
Undervoltage lockout state: VCC = 8 V
0.85
1
mA
ICC(INHIBIT)
VCC = 12 V, OV/UV < VSD(L)
1.35
1.7
mA
LCS700
LCS701
LCS702
LCS703
LCS705
LCS708
LCS700
LCS701
LCS702
LSC703
LCS705
4.0
4.4
4.9
5.4
6.6
8.8
3.4
3.9
4.3
4.7
5.8
5.2
5.8
6.5
7.1
8.8
11.8
4.6
5.2
5.8
6.4
7.9
LCS708
7.8
10.7
Inhibit Current
VCC Operating
Current
VCCH Operating
Current
ICC(ON)
Typical at VCC = 12 V
Maximum at VCC =
15 V Measured at
300 kHz, HB Open
and VD = 15 V
ICCH(ON)
Typical at VCCH = 12 V
Maximum at VCCH =
15 V Measured at
300 kHz, HB Open
and VD = 15 V
mA
mA
VCC Supply Undervoltage Lockout
VCC Start Threshold
VUVLO(+)
Device exits UVLO state when VCC exceeds
UVLO+
10
10.7
11.4
V
VCC Shutdown
Threshold
VUVLO(-)
Device enters UVLO state when VCC falls
below UVLO+
9.1
9.8
10.5
V
0.70
0.90
1.20
V
VCC Start-Up/Shutdown Hysteresis
VUVLO(HYST)
20
Rev. B 062011
www.powerint.com
LCS700-708
Parameter
Symbol
Conditions
SOURCE = 0 V; TJ = 0 to 100 °C
VCC = 12 V, VCCH = 12 V
Min
Typ
Max
Units
(Unless Otherwise Specified)
VCCH Supply Undervoltage Lockout
VCCH Start Threshold
VUVLO(H+)
Driver exits UVLO state when VCCH exceeds
UVLOH+
8.2
8.5
8.9
V
VCCH Shutdown
Threshold
VUVLO(H-)
Driver enters UVLO state when VCCH falls
below UVLOH-
7.4
7.5
8.1
V
0.65
0.75
1.00
V
VCCH Start-Up/
Shutdown Hysteresis
VUVLO(H)HYST
High-Voltage Supply Undervoltage/Overvoltage Enable
OV/UV Overvoltage
Shutdown Threshold
VOV(H)
Overvoltage assertion threshold
129
131
133
% of
VSD(H)
OV/UV Overvoltage
Recovery Threshold
VOV(L)
Overvoltage de-assertion threshold
124
126
128
% of
VSD(H)
OV/UV Undervoltage
Start Threshold
VSD(H)
Undervoltage de-assertion threshold
2.35
2.40
2.45
V
OV/UV Undervoltage
Shutdown Threshold
VSD(L)
Undervoltage assertion threshold
77
79
81
% of
VSD(H)
RIN(OVUV)
OV/UV pin resistance to G
3.0
5.0
6.6
MW
Reference Voltage
VREF
IREF = 4 mA
3.25
3.40
3.50
V
Current Source
Capability of VREF Pin
IREF
4
mA
VREF Capacitance
CREF
OV/UV Pin
Input Resistance
Reference
Required external coupling on VREF pin
1
mF
LLC Oscillator
25
1000
RFB = 37.9 kW to VREF , 180 kHz
-5.0
5.0
FMIN(ACL)
RFB = 154 kW to VREF , 50 kHz
-7.5
7.5
FMAX(ACC)
IFB = IDT/BF, RFMAX = 12.5 kW,
FMAX = 510 kHz
-7.5
7.5
%
DLLC
Duty symmetry of the half-bridge waveform, CFB = 4.7 nF, CDT/BF = 4.7 nF, 250 kHz.
Use recommended layout
49
51
%
tD
RFMAX = 7 kW, RBURST = 39.6 kW
Frequency Range
FRANGE
Accuracy of Minimum
Frequency Limit
FMIN(ACC)
Accuracy of Maximum
Frequency Limit
Duty Balance
Dead-TimeB
DT/BF Control
Current Range
IFB Threshold to Stop
LLC Switching
IDT/BF
330
30
Threshold applies after exiting soft-start
mode for burst setting BT1
49.8
ISTOP2
Threshold applies after exiting soft-start
mode for burst setting BT2
43.9
ISTOP3
Threshold applies after exiting soft-start
mode for burst setting BT3
37.1
%
ns
430
ISTOP1
kHz
mA
% of IDT/BF
21
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Rev. B 062011
LCS700-708
Parameter
Symbol
Conditions
SOURCE = 0 V; TJ = 0 to 100 °C
VCC = 12 V, VCCH = 12 V
Min
Typ
Max
Units
% of IDT/BF
(Unless Otherwise Specified)
LLC Oscillator (cont.)
IFB Threshold
Hysteresis
IBURST(HYST)
ISTART is IBURST(HYST) below ISTOP
5
6.25
8
VBT1
Required VDT/BF at start-up to enable burst
setting BT1
93.5
95
96.3
VBT2
Required VDT/BF at start-up to enable burst
setting BT2
88.5
90
91.3
VBT3
Required VDT/BF at start-up to enable burst
setting BT3
83.5
85
86.3
RCDT/BF
This time constant must be less than the
specified maximum to ensure correct
setting of burst mode.
FB Current Maximum
IFB
Determines the maximum control
frequency that can be set by IFB.
FB Control
Current Range
IFB
IFB is limited by the current into DT/BF
FB Virtual Voltage
VFB
FB input appears as RIN(FB) in series with
VFB. 30 mA < IFB < IDT/BF
0.65
V
FB Input Resistance
RIN(FB)
FB input appears as RIN(FB) in series with
VFB. 30 mA < IFB < IDT/BF
2.5
kW
FB Input Resistance
During Soft-Start
RFB(SS)
FB input appears as RFB(SS) in series with
VREF during the soft-start delay interval or
when OV/UV < VSD or OV/UV > VOV
750
W
DT/BF Voltage to
Program Burst Setting
Time Constant for the
Combination of RFMAX,
RBURST and the Decoupling Cap on DT/BF
100
100
15
% of VREF
ms
%IDT/BF
430
mA
Over-Current Protection
Fast Over-Current
Fault Voltage
Threshold4
VIS(F)
Slow Over-Current
Fault Voltage
Threshold
VIS(S)
7 LLC clock cycle debounce
Over-Current Fault
Pulse Width
tIS
Minimum time VIS exceeds VIS(F)/VIS(S) per
cycle to trigger fault protection
0.855
0.905
0.955
V
0.455
0.505
0.555
V
30
ns
140
°C
Over-Temperature Protection
Over-Temperature
Shutdown ThresholdA
TOT
NOTES:
A. Guaranteed by design.
B. Typical apparent dead-time at the HB pin under resonant ZVS conditions.
C. VCC/VCCH operating range to achieve power capabilities specified in data sheet power table.
22
Rev. B 062011
www.powerint.com
LCS700-708
14
14
12
Current (mA)
12
10
8
6
LCS700
LCS701
LCS702
LCS703
LCS705
LCS708
4
2
100
20
300
400
500
600
700
8
6
2
0
800
0
Frequency (kHz)
700
600
500
400
300
LCS700
LCS701
LCS702
LCS703
LCS705
LCS708
200
100
400
500
Frequency (kHz)
Figure 29. Control Power vs. Frequency.
400
500
600
700
800
600
700
LCS700
LCS701
LCS702
LCS703
LCS705
LCS708
1000
800
600
400
200
0
300
300
1200
Capacitance (pF)
PI-6183-112910
800
20
20
Figure 28. VCCH Current vs. Frequency.
900
100
100
Frequency (kHz)
Figure 27. VCC Current vs. Frequency.
0
LCS700
LCS701
LCS702
LCS703
LCS705
LCS708
PI-6184-112910
0
10
4
0
Power (mW)
PI-6182-112910
16
Current (mA)
16
PI-6181-112910
18
800
0
0
50
100
150
200
250
300
350
400
Half-Bridge Voltage (V)
Figure 30. Half-Bridge Small Signal Capacitance vs. Half-Bridge Voltage.
23
www.powerint.com
Rev. B 062011
Rev. B 062011
1
5
6
9
10 11
END VIEW
0.628 (15.95) Ref.
0.060 (1.52) Ref.
FRONT VIEW
7 8
Pin 1 I.D.
0.653 (16.59)
0.647 (16.43)
0.038 (0.97)
3 4
0.019 (0.48) Ref.
A
2
13 14
16
2
0.048 (1.22)
0.046 (1.17)
0.140 (3.56)
0.120 (3.05)
Detail A
SIDE VIEW
0.118 (3.00)
0.047 (1.19)
0.016 (0.41)
Ref.
0.290 (7.37)
Ref.
0.027 (0.70)
0.023 (0.58)
0.020 (0.50)
Detail A (Scale = 9×)
0.016 (0.41) 13×
0.011 (0.28)
0.020 M 0.51 M C
3
0.021 (0.53)
0.019 (0.48)
10° Ref.
All Around
0.056 (1.42) Ref.
0.325 (8.25)
0.320 (8.13)
B
0.081 (2.06)
0.077 (1.96)
C
eSIP-16C (H Package)
3
Dimensions in inches, (mm).
All dimensions are for reference.
PCB FOOT PRINT
0.118 (3.00)
0.029 Dia Hole
0.062 Dia Pad
BACK VIEW
4
0.024 (0.61) 13×
0.019 (0.48)
0.010 M 0.25 M C A B
0.207 (5.26)
0.187 (4.75)
0.210 (5.33)
Ref.
Notes:
1. Dimensioning and tolerancing per ASME Y14.5M-1994.
2. Dimensions noted are determined at the outermost
extremes of the plastic body exclusive of mold flash,
tie bar burrs, gate burrs, and interlead flash, but
including any mismatch between the top and bottom
of the plastic body. Maximum mold protrusion is 0.007
[0.18] per side.
3. Dimensions noted are inclusive of plating thickness.
4. Does not include interlead flash or protrusions.
5. Controlling dimensions in inches (mm).
PI-5639-031011
0.076 (1.93)
0.038 (0.97)
0.012 (0.30) Ref.
0.076 (1.93)
0.519 (13.18)
Ref.
0.214 (5.44)
Ref.
LCS700-708
24
www.powerint.com
LCS700-708
Part Ordering Information
• Hiper Product Family
• LCS Series Number
• Package Identifier
H
Plastic eSIP-16C
• Pin Finish
G
Halogen Free and RoHS Compliant
• Tape & Reel and Other Options
LCS 700
H
G - TL
Blank
Standard Configurations
25
www.powerint.com
Rev. B 062011
Revision
B
Notes
Date
Initial Release
06/20/11
For the latest updates, visit our website: www.powerint.com
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Integrations does not assume any liability arising from the use of any device or circuit described herein. POWER INTEGRATIONS MAKES
NO WARRANTY HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY
RIGHTS.
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The products and applications illustrated herein (including transformer construction and circuits external to the products) may be covered
by one or more U.S. and foreign patents, or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A
complete list of Power Integrations patents may be found at www.powerint.com. Power Integrations grants its customers a license under
certain patent rights as set forth at http://www.powerint.com/ip.htm.
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POWER INTEGRATIONS PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR
SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF POWER INTEGRATIONS. As used herein:
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2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause
the failure of the life support device or system, or to affect its safety or effectiveness.
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trademarks are property of their respective companies. ©2011, Power Integrations, Inc.
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