InnoSwitch3-ProCurrent Limit Operation capacitive loads without extending the start-up time. The primary-side control er has a current limit threshold ramp that is Input Line Voltage Monitoring inversely proportional to the time from the end of the previous The UNDER/OVER INPUT VOLTAGE
pin is used for input undervoltage primary switching cycle (i.e. from the time the primary switch turns and overvoltage sensing and protection. off at the end of a switching cycle). A sense resistor is tied between the high-voltage DC bulk capacitor This characteristic produces a primary current limit that increases as after the bridge (or to the AC side of the bridge rectifier for fast AC the switching frequency (load) increases (Figure 6). reset) and the UNDER/OVER INPUT VOLTAGE
pin to enable this This algorithm enables the most efficient use of the primary switch functionality. This function can be disabled by shorting the UNDER/ with the benefit that this algorithm responds to digital feedback OVER INPUT VOLTAGE pin to primary GND. information immediately when a feedback switching cycle request is At power-up, after the primary bypass capacitor is charged and the received. ILIM state is latched, and prior to switching, the state of the UNDER/ At high load, switching cycles have a maximum current approaching OVER INPUT VOLTAGE pin is checked to confirm that it is above the 100% I . This gradual y reduces to 30% of the full current limit as brown-in and below the overvoltage shutdown thresholds. LIM load decreases. Once 30% current limit is reached, there is no In normal operation, if the UNDER/OVER INPUT VOLTAGE pin current further reduction in current limit (since this is low enough to avoid fal s below the brown-out threshold and remains below brown-in for audible noise). The time between switching cycles will continue to longer than t , the control er enters auto-restart. Switching will only increase as load reduces. UV- resume once the UNDER/OVER INPUT VOLTAGE pin current is above Jitter the brown-in threshold. The normalized current limit is modulated between 100% and 95% at a modulation frequency of f this results in a frequency jitter of In the event that the UNDER/OVER INPUT VOLTAGE pin current is M ~7 kHz with average frequency of ~100 kHz. above the overvoltage threshold, the control er will also enter auto-restart. Again, switching will only resume once the UNDER/ Auto-Restart OVER INPUT VOLTAGE pin current has returned to within its normal In the event a fault condition occurs (such as an output overload, operating range. output short-circuit, or external component/pin fault), the InnoSwitch3-Pro enters auto-restart (AR) or latches off. The latching The input line UV/OV function makes use of a internal high-voltage condition is reset by bringing the PRIMARY BYPASS pin below ~ 3 V (V ) switch on the UNDER/OVER INPUT VOLTAGE pin to reduce V or by going below the UNDER/OVER INPUT VOLTAGE pin UV (I ) power consumption. The control er samples the input line at light UV- threshold. load conditions when the time between switching cycles is 50 msec or more. At <50 msec between switching cycles, the high-voltage In auto-restart, switching of the power switch is disabled for t . AR(OFF) switch will remain on making sensing continuous. There are 2 ways to enter auto-restart: Primary-Secondary Handshake 1. Continuous secondary requests at above the overload detection At start-up, the primary-side initial y switches without any feedback frequency (~110 kHz) for longer than 82 ms (t ). information (this is very similar to the operation of a standard AR 2. No requests for switching cycles from the secondary for > t . TOPSwitch™, TinySwitch™ or LinkSwitch™ control ers). AR(SK) The second is included to ensure that if communication is lost, the If no feedback signals are received during the auto-restart on-time primary tries to restart. Although this should never be the case in (t ), the primary goes into auto-restart mode. Under normal AR normal operation, it can be useful when system ESD events (for conditions, the secondary control er will power-up via the FORWARD example) causes a loss of communication due to noise disturbing the pin or from the OUTPUT VOLTAGE pin and take over control. From secondary control er. The issue is resolved when the primary restarts this point onwards the secondary controls switching. after an auto-restart off-time. If the primary control er stops switching or does not respond to cycle The auto-restart is reset as soon as an AC reset occurs. requests from the secondary during normal operation (when the SOA Protection secondary has control), the handshake protocol is initiated to ensure In the event that there are two consecutive cycles where the drain that the secondary is ready to assume control once the primary current is reached 110% of I within ~500 ns, the control er will skip begins to switch again. An additional handshake is also triggered if LIM 2.5 cycles or ~25 ms (based on full frequency of 100 kHz). This provides sufficient time for the transformer to reset with large 5 Rev. G 07/19 www.power.com Document Outline Product Highlights Description Output Power Table Pin Functional Description InnoSwitch3-Pro Functional Description Primary Controller Secondary Controller Register Definition Command Registers Telemetry (Read-back) Registers I2C Connection I2C Example Waveforms Applications Example Key application Considerations Selection of Components Components for InnoSwitch3-Pro IC Primary-Side Circuit Components for InnoSwitch3-PRO Secondary-Side Circuit Recommendations for Circuit Board Layout Layout Example Recommendations for Transformer Design Application Considerations for INN3379C and INN3370C Only Quick Design Checklist Theremal Resistance Test Conditions for INN3379C and INN3370C Absolute Maximum Ratings Thermal Resistance Key Electrical Characteristics Typical Performance Curves InSOP-24D Package Drawing Part Ordering Table MSL Table ESD and Latch-Up Table Part Ordering Information
