Datasheet LYTSwitch-6 (Power Integrations) - 4

LYTSwitch-6 Primary Controller
1.05 The LYTSwitch-6 features variable frequency QR control er + CCM operation for enhanced efficiency and extended output power
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1.0 capability. -8205-120516
(A
PI
PRIMARY BYPASS Pin Regulator
0.95
LIM
The PRIMARY BYPASS pin has an internal regulator that charges the PRIMARY BYPASS pin capacitor to V by drawing current from the BPP 0.9 voltage on the DRAIN pin whenever the power MOSFET is off. The PRIMARY BYPASS pin is the internal supply voltage node. When the power MOSFET is on, the device operates from the energy stored in 0.85
ormalized I
the PRIMARY BYPASS pin capacitor.
N
0.8 In addition, there is a shunt regulator clamping the PRIMARY BYPASS pin voltage to V when the current is provided to the PRIMARY SHUNT BYPASS pin through an external resistor. This facilitates powering the 0.75 LYTSwitch-6 external y through a bias winding to decrease the 30 40 50 60 70 80 90 100 no-load consumption to less than 15 mW.
Steady-State Switching Frequency (kHz) Primary Bypass ILIM Programming
LYTSwitch-6 has user programmable current limit (ILIM) settings Figure 6. Normalized Primary Current vs. Frequency. through the selection of PRIMARY BYPASS pin capacitor value. The PRIMARY BYPASS pin can use a ceramic capacitor for decoupling the
Current Limit Operation
internal supply of the device. The primary-side control er has a current limit threshold ramp that is inversely proportional to time from the end of the last primary There are (2) programmable settings using 0.47 mF and 4.7 mF for switching cycle (i.e. from the time the primary FET turns off at the standard and increased ILIM settings respectively. end of a switching cycle).
Primary Bypass Undervoltage Threshold
The characteristic produces a primary current limit that increases as The PRIMARY BYPASS pin undervoltage circuitry disables the power the load increases (Figure 6). MOSFET when the PRIMARY BYPASS pin voltage drops below ~4.5 V (V - V ) in steady-state operation. Once the PRIMARY BYPASS This algorithm enables the most efficient use of the primary switch BPP BP(H) pin voltage fal s below this threshold, it must rise back to V to with immediate response when a feedback switching cycle request is SHUNT re-enable turn-on of the power MOSFET. received.
Primary Bypass Output Overvoltage Auto-Restart Function
At high load, switching cycle have a maximum current approaching The PRIMARY BYPASS pin has an OV protection non-latching feature. 100% ILIM gradual y reduced to 30% of the full current limit as the A Zener diode in paral el to the resistor in series with the PRIMARY load reduces. Once 30% current limit is reached, there is no further BYPASS pin capacitor is typical y used to detect an overvoltage on the reduction in current limit (since this is low enough to avoid audible primary bias winding to activate this protection mechanism. In the noise) but the time between switching cycles will continue to reduce event the current into the PRIMARY BYPASS pin exceeds I , the SD as load reduces. device will disable the power MOSFET switching for a time t . AR(OFF) After this time the control er will restart operation and attempt to
Jitter
return to regulation. The normalized current limit is modulated between 100% and 95% at a modulation frequency of f this results in a frequency jitter of ~7 kHz M This VOUT OV protection is also available as an integrated feature on with average frequency of ~100 kHz. the secondary control er.
Auto-Restart Over-Temperature Protection
In the event a fault condition occurs such as an output overload, The thermal shutdown circuitry senses the primary MOSFET die output short-circuit, or external component/pin fault, the LYTSwitch-6 temperature. The threshold is typical y set to T with T enters into auto-restart (AR) operation. In auto-restart the power SD SD(H) hysteresis. When the die temperature rises above this threshold the MOSFET switching is disabled for t . There are 2 ways to enter AR(OFF) power MOSFET is disabled and remains disabled until the die auto-restart: temperature fal s by T at which point it is re-enabled. A large SD(H) hysteresis of T is provided to prevent over-heating of the PCB due 1. Continuous secondary requests at above the overload detection SD(H) to continuous fault condition. frequency (~110 kHz) for longer than 80 ms. 2. No requests for switching cycles from the secondary for > t . AR(SK)
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Rev. E 02/18 www.power.com Document Outline Product Highlights Description Output Power Table Pin Functional Description LYTSwitch-6 Functional Description Primary Controller Secondary Controller Application Example Key Applications Design Considerations Primary-Side Components of LYTSwitch-6 Secondary-Side Components of f LYTSwitch-6 Recommendations for Circuit Board Layout Recommended Position of InSOP-24D Package with Respect to Transformer Quick Design Checklist Other Applications Design Example PCB Layout Example Absolute Maximum Ratings Thermal Resistance Key Electrical Characteristics Typical Performance Curves InSOP-24D Package Drawing MSL Table ESD and Latch-Up Table Part Ordering Information