lnk603 Power Integrations, Inc., lnk603 Datasheet - Page 3

• Manufacturer Part Number: lnk603
• Description: Energy-efficient, Accurate Cv/cc Switcher For Adapters And Chargers
• Manufacturer: Power Integrations, Inc.

LinkSwitch-II Functional Description
The LinkSwitch-II combines a high voltage power MOSFET
switch with a power supply controller in one device. Similar to
the LinkSwitch-LP and TinySwitch-III it uses ON/OFF control to
regulate the output voltage. In addition, the switching frequency
is modulated to regulate the output current to provide a
constant current characteristic. The LinkSwitch-II controller
consists of an oscillator, feedback (sense and logic) circuit, 6 V
regulator, over-temperature protection, frequency jittering,
current limit circuit, leading-edge blanking, inductance
correction circuitry, frequency control for constant current
regulation and on/off state machine for CV control.
Inductance Correction Circuitry
If the primary magnetizing inductance is either too high or low
the converter will automatically compensate for this by adjusting
the oscillator frequency. Since this controller is designed to
operate in discontinuous-conduction mode the output power is
directly proportional to the set primary inductance and its
tolerance can be completely compensated with adjustments to
the switching frequency.
Constant Current (CC) Operation
As the output voltage and therefore the Flyback voltage across
the bias winding increases, the feedback pin voltage increases.
The switching frequency is adjusted as the feedback pin voltage
increases to provide a constant output current regulation. The
constant current circuit and the inductance correction circuit
are designed to operate concurrently in the CC region.
Constant Voltage (CV) Operation
As the feedback pin approaches V
regulation mode, the power supply transitions into CV
operation. The switching frequency at this point is at its
maximum value, corresponding to the peak power point of the
CCCV characteristic. The controller regulates the feedback pin
voltage to remain at V
feedback pin voltage is sampled 2.5 μs after the turn-off of the
high voltage switch. At light loads the current limit is also
reduced to decrease the transformer fl ux density.
Output Cable Compensation
This compensation provides a constant output voltage at the
end of the cable over the entire load range in CV mode. As the
converter load increases from no-load to the peak power point
(transition point between CV and CC) the voltage drop
introduced across the output cable is compensated by
increasing the feedback pin reference voltage. The controller
determines the output load and therefore the correct degree of
compensation based on the output of the state machine. Cable
drop compensation for a 24 AWG (0.3 Ω) cable is selected with
C
Auto-Restart and Open-Loop Protection
In the event of a fault condition such as an output short or an
open loop condition the LinkSwitch-II enters into an appropriate
protection mode as described below.
www.powerint.com
BP
= 1 μF and for a 26 AWG (0.49 Ω) cable with C
FBth
using an on/off state-machine. The
FBth
from the constant current
PB
= 10 μF.
In the event the feedback pin voltage during the Flyback period
falls below 0.7 V before the feedback pin sampling delay
(~2.5 μs) for a duration in excess of ~450 ms (auto-restart on-
time (t
power MOSFET is disabled for 4 seconds (~8% Auto-Restart
duty cycle). The auto-restart alternately enables and disables
the switching of the power MOSFET until the fault condition is
removed.
In addition to the conditions for auto-restart described above, if
the sensed feedback pin current during the Forward period of
the conduction cycle (switch “on” time) falls below 120 μA, the
converter annunciates this as an open-loop condition (top
resistor in potential divider is open or missing) and reduces the
Auto-restart time from 450 msec to approximately 6 clock cycles
(90 μs), whilst keeping the disable period of 4 seconds. This
effectively reduces the Auto-Restart duty cycle to less than 0.01%.
Over-Temperature Protection
The thermal shutdown circuitry senses the die temperature. The
threshold is set at 142 °C typical with a 60 °C hysteresis. When
the die temperature rises above this threshold (142 °C) the
power MOSFET is disabled and remains disabled until the die
temperature falls by 60 °C, at which point the MOSFET is
re-enabled.
Current Limit
The current limit circuit senses the current in the power
MOSFET. When this current exceeds the internal threshold
(I
cycle. The leading edge blanking circuit inhibits the current limit
comparator for a short time (t
turned on. This leading edge blanking time has been set so that
current spikes caused by capacitance and rectifi er reverse
recovery time will not cause premature termination of the
MOSFET conduction. The LinkSwitch-II also contains a “di/dt”
correction feature to minimize CC variation across the input line
range.
6.0 V Regulator
The 6 V regulator charges the bypass capacitor connected to
the BYPASS pin to 6 V by drawing a current from the voltage on
the DRAIN, whenever the MOSFET is off. The BYPASS pin is
the internal supply voltage node. When the MOSFET is on, the
device runs off of the energy stored in the bypass capacitor.
Extremely low power consumption of the internal circuitry
allows the LinkSwitch-II to operate continuously from the
current drawn from the DRAIN pin. A bypass capacitor value of
either 1 μF or 10 μF is suffi cient for both high frequency
decoupling and energy storage.
LIMIT
), the power MOSFET is turned off for the remainder of that
AR-ON
) the converter enters into Auto-restart, wherein the
LNK603-606/613-616
LEB
) after the power MOSFET is
Rev. C 06/08
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