Datasheet InnoSwitch-CP (Power Integrations) - 4

InnoSwitch-CP Over-Temperature Protection
the primary goes into auto-restart and repeats. However under The thermal shutdown circuitry senses the primary die temperature. normal conditions, the secondary chip will power-up through the This threshold is typical y set to 142 °C with 75 °C hysteresis. When FORWARD pin or directly from VOUT and then take over control. the die temperature rises above this threshold the power MOSFET is From then onwards the secondary is in control of demanding disabled and remains disabled until the die temperature fal s by 75 °C, switching cycles when required. at which point it is re-enabled. A large hysteresis of 75 °C is provided to prevent over-heating of the PC board due to continuous fault The handshake flowchart is shown in Figure 7 below. condition. In the event the primary stops switching or does not respond to cycle
Current Limit Operation
requests from the secondary during normal operation when the The current limit circuit senses the current in the power MOSFET. secondary has control, the handshake protocol is initiated to ensure When this current exceeds the internal threshold (I ), the power that the secondary is ready to assume control once the primary LIMIT MOSFET is turned off for the remainder of that switch cycle. The begins switching again. This protocol for an additional handshake is current limit state-machine reduces the current limit threshold by also invoked in the event the secondary detects that the primary is discrete amounts under medium and light loads. providing more cycles than were requested. The leading edge blanking circuit inhibits the current limit comparator for a short time (t ) after the power MOSFET is turned-on. This LEB leading edge blanking time has been set so that current spikes P: Primary Chip caused by capacitance and secondary-side rectifier reverse recovery S: Secondary Chip time will not cause premature termination of the switching pulse. Start P: Powered Up, Switching Each switching cycle is terminated when the Drain current of the S: Powering Up primary power MOSFET reaches the current limit of the device.
Auto-Restart
In the event of a fault condition such as output overload, output P: Auto-Restart short-circuit or external component/pin fault, the InnoSwitch-CP S: Powering Up enters into auto-restart (AR) operation. In auto-restart operation the power MOSFET switching is disabled for t . There are 2 ways to AR(OFF) enter auto-restart: 2s 1. Continuous switching requests from the secondary for time period S: Has powered No P: Goes to Auto-Restart Off exceeding t . up within t AR AR S: Bypass Discharging 2. No requests for switching cycles from the secondary for a time period exceeding t . AR(SK) Yes The first condition corresponds to a condition wherein the secondary tAR control er makes continuous cycle requests without a skipped-cycle P: Switching for more than t time period. The second method was included to S: Sends Handshaking Pulses AR ensure that if communication is lost, the primary tries to restart again. Although this should never be the case in normal operation, this can be useful in the case of system ESD events for example where a loss of communication due to noise disturbing the secondary control er, is resolved when the primary restarts after an auto-restart P: Has Received No P: Continuous Switching Handshaking S: Doesn’t Take Control off time. Pulses The auto-restart alternately enables and disables the switching of the Yes power MOSFET until the fault is removed. The auto-restart counter is gated by the switch oscillator in SOA mode the auto-restart off timer P: Stops Switching, Hands may appear to be longer. Over Control to Secondary The auto-restart counter is reset once the PRIMARY BYPASS pin fal s below the undervoltage threshold V -V . BPP BPP(HYS)
Safe-Operating-Area (SOA) Protection
In the event there are two consecutive cycles where the primary S: Has Taken No P: Not Switching Control? power MOSFET switch current reaches current limit (I ) within the S: Doesn’t Take Control LIM blanking (t ) plus the current limit (t ) delay time, the control er will LEB ILD skip approximately 2.5 cycles or ~25 msec. This provides sufficient Yes time for reset of the transformer without sacrificing start-up time into large capacitive load. Auto-restart timing is increased when the End of Handshaking, device is operating in SOA-mode. Secondary Control Mode
Primary-Secondary Handshake Protocol
PI-7416-102116 At start-up, the primary initial y switches without any feedback information (this is very similar to the operation of a standard TOPSwitch™, TinySwitch™ or LinkSwitch™ control ers). If no Figure 7. Primary –Secondary Handshake Flowchart. feedback signals are received during the auto-restart on-time,
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Rev. F 09/17 www.power.com Document Outline Product Highlights Highly Integrated, Compact Footprint EcoSmart - Energy Efficient Advanced Protection / Safety Features Full Safety and Regulatory Compliance Green Package Applications Description Output Power Table Pin Functional Description InnoSwitch-CP Functional Description InnoSwitch-CP Operation Applications Example Key application Considerations Selection of Components Recommendations for Circuit Board Layout Recommendations for EMI Reduction Recommendations for Audible Noise Suppression Recommendations for Transformer Design Quick Design Checklist Absolute Maximum Ratings Thermal Resistance Key Electrical Characteristics NOTES Typical Performance Characteristics eSOP-R16B Package Package Marking MSL Table ESD and Latch-Up Table Part Ordering Information