Datasheet LYTSwitch-6 (Power Integrations) - 13

LYTSwitch-6 Common Primary Clamp Configurations R2CD R2CD (Zener Clamp) R2CD + Zener
R R SN VR VR SN CSN CLAMP CLAMP D C D CLAMP SN CLAMP R D R R s CLAMP S S D D D PI-8582-011218 PI-8584-011218 PI-8583-011218 Figure 13. Recommended Primary Clamp Components.
Primary Clamp Circuit Benefits RCD Zener RCD + Zener
Component Cost Low Medium High No-Load Input Power High Low Medium Light-Load Efficiency Low High Medium EMI Suppression High Low Medium Table 2. Benefits of Primary Clamp Circuits.
Secondary-Side Components of f LYTSwitch-6 FEEDBACK Pin Divider Network (R , R FB(UPPER) FB(LOWER)
A suitable resistor voltage divider should be connected from the
Secondary Bypass Pin Capacitor (C ) BPS
output of the power supply to the FEEDBACK pin of the LYTSwitch-6 This capacitor works as a supply decoupling capacitor for the internal IC such that for the desired output voltage, the voltage at the secondary-side control er. A surface-mount, 2.2 mF, 25 V, multi-layer FEEDBACK pin will be 1.265 V. A decoupling capacitor (C ) of 330 pF ceramic capacitor is recommended for satisfactory operation of the FB is recommended to be connected from the FEEDBACK pin to IC. Since the SECONDARY BYPASS pin voltage needs to reach 4.4 V SECONDARY GROUND pin and serves as a decoupling capacitor for earlier than output voltage reaches to the regulation voltage level, the FEEDBACK pin to prevent switching noise from affecting operation the significantly higher secondary bypass capacitor value will lead to of the IC. output voltage overshoot during start-up. The values lower than 1.5 mF may not be enough capacitance, which can cause unpredictable
SR MOSFET Operation and Selection
operation. The capacitor must be located adjacent to the IC pins. Although a simple diode rectifier and filter works for the output, use The 25 V rating is necessary to guarantee the actual value in of a SR FET enables the significant improvement in operating operation since the capacitance of ceramic capacitors drops with efficiency often necessary to meet the European CoC and the U.S. applied voltage. 10 V rated capacitors are not recommended for this DoE energy efficiency requirements. The secondary-side control er reason. Capacitors with X5R or X7R dielectrics should be used for turns on the SR FET once the flyback cycle begins. The SR FET gate best results. should be tied directly to the SYNCHRONOUS RECTIFIER DRIVE pin of the LYTSwitch-6 IC (no additional resistors should be connected in
FORWARD Pin Resistor (R ) FWD
the gate circuit of the SR FET). The SR FET is turned off once the V The FORWARD pin is connected to the Drain terminal of the DS of the SR FET reaches 0 V. A FET with 18 mW R is appropriate synchronous rectifier MOSFET (SR FET). This pin is used to sense DS(ON) for a 5 V, 2 A output, and a FET with 8 mW R is suitable for the Drain voltage of the SR FET to precisely turn-on and turn-off. DS(ON) designs rated with a 12 V, 3 A output. The SR FET driver uses the This pin is also used to provide charge to the SECONDARY BYPASS SECONDARY BYPASS pin for its supply rail, and this voltage is pin capacitance whenever output voltage is lower than the secondary typical y 4.4 V. A FET with a high threshold voltage is therefore not bypass voltage. A 47 Ω, 5% resistor is recommended to ensure suitable; FETs with a threshold voltage of 1.5 V to 2.5 V are ideal sufficient IC supply current and works for very wide range of output although MOSFETs with a threshold voltage (absolute maximum) as voltages. A higher or lower resistor value should not be used as it high as 4 V may be used provided their data sheets specify R can affect device operation such as the timing of the synchronous DS(ON) across temperature for a gate voltage of 4.5 V. rectifier drive. Care should be taken to ensure that the voltage at the FORWARD pin never exceeds its absolute maximum voltage. If in any design, the FORWARD pin voltage exceeds the FORWARD pin absolute maximum voltage, the IC will be damaged.
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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