LNK4322S

LinkSwitch-4 Family Energy-Efficient, Accurate Primary-Side Regulated CV/CC Switcher for Adapters and Chargers Product Highlights + Dramatically Simplifies CV/CC Converters • Eliminates optocoupler and all secondary CV/CC control circuitry • Eliminates all control loop compensation circuitry Advanced Performance Features • Dynamic base drive technology provides flexibility in choice of BJT LinkSwitch-4 U1 LNK4xx2S ~ Compensates for input line voltage variations Compensates for cable voltage drop Compensates for external component temperature variations Very accurate IC parameter tolerances using proprietary trimming technology • Frequency up to 65 kHz to reduce transformer size • The minimum peak current is fixed to improve transient load response Enhanced Performance Features • Easy start for starting into capacitive loads (LNK4114D, LNK4115D) • Constant power for high current start-up (LNK4214D, LNK4215D) • 13003 drive improved efficiency with 13003 BJT’s (LNK4302S, FB GND • Extends RBSOA of BJT • Dramatically reduces sensitivity to BJT gain • • • • VCC CS transistor by dynamically optimizing BJT switching characteristics BD ED PI-7462-122315 Figure 1. Typical Application (SOT-23-6) (S). + BD ED ~ VCC LinkSwitch-4 U1 LNK40x3D CS LNK4322S) SBD FB GND Advanced Protection/Safety Features • Single fault output overvoltage and short-circuit • Over-temperature protection • Active clamp EcoSmart™– Energy Efficient • Meets DoE 6 and CoC V5 2016 via an optimized quasi-resonant switching PWM/PFM control Output Power Table 85 - 265 VAC Product3,4 • No-load consumption of IFBHT(START)), the LinkSwitch-4 will enter Run mode and drive pulses will be output on the BASE DRIVE pin. To achieve smooth power-up (monotonic rise in VOUT), C VCC must be large enough to power the control circuitry during Initialize mode and the first few cycles of Run mode, until sufficient power is provided by the transformer voltage supply winding. If the input voltage falls below VMAINS(LO) (see Input Undervoltage Protection), V VCC will fall below V VCC(SLEEP) and the LinkSwitch-4 will go into Sleep mode, reducing its current consumption to IVCC(SLEEP). The control circuitry will re-initialize if the input voltage is restored and V VCC reaches V VCC(RUN). VVCC(RUN) VVCC VVCC(SLEEP) Off Sleep Initialize Run Sleep Off PI-7457-010815 Figure 7. VCC Waveforms. Mode Description Sleep From initial application of input power or from Run mode, if V VCC falls below V VCC(SLEEP), the LinkSwitch-4 goes to Sleep mode. Non-essential circuits are turned off. Base and Emitter drives are turned off so BASE DRIVE and EMITTER DRIVE pins become high impedance, allowing the bootstrap resistor (RHT) and BJT to start the circuit. Sleep mode is exited when V VCC rises to V VCC(RUN) and the control circuitry goes to Initialize mode. Initialize Internal circuits are enabled and the LinkSwitch-4 issues one switching cycle to sample the input voltage via the FEEDBACK pin. If VIN (hence VHT) is high enough, the LinkSwitch-4 changes to Run mode. If VIN is not high enough, no further base drive pulses are issued and the LinkSwitch-4 returns to Sleep mode when V VCC falls below V VCC(SLEEP). Run Power conversion: The control circuitry is powered from the VCC rail and the internal VDD is regulated. If V VCC falls below V VCC(SLEEP), the IC ceases power conversion and goes to Sleep mode. Table 2. Summary of LinkSwitch-4 Operating Modes. 4 Rev. F 05/18 www.power.com LinkSwitch-4 Switching Waveforms Typical waveforms at the feedback and primary current sense inputs are shown in Figure 8. tSAMP VFBREG FB 0V tCSB 0V CS VCSTHR tFON VVCC(RUN) 0A BD ON OFF ED Transformer Flux PI-7458-010815 Figure 8. Typical Waveforms at the Feedback and Primary Current Sense Inputs. Constant Voltage (CV) Regulation Constant output voltage regulation is achieved by sensing the voltage at the feedback input, which is connected to the voltage supply winding as shown in Figure 10 or to a dedicated feedback winding. An internal current source prevents the feedback voltage from going negative. A typical feedback voltage waveform is shown in Figure 8. The feedback waveform is continuously analyzed and sampled at time tSAMP to measure the reflected output voltage. tSAMP is identified by the slope of the feedback waveform and is coincident with zero flux in the transformer. The sampled voltage is regulated at VFB(REG) by the voltage control loop. The (typical) CV mode output voltage is set by the ratio of resistors RFB1 and RFB2 (see Figure 10) and by the transformer turns ratio, according to the following formula (where output diode voltage is neglected): N R VOUT^CV h = V FB^ REG h a 1 + R FB1 ka N S k FB2 F Where NF is the number of turns on the feedback (or voltage supply if used for feedback) winding and NS is the number of turns on the secondary winding. The tolerances of RFB1 and RFB2 affect output voltage regulation and mains estimation so should typically be chosen to be 1% or better. The current required to clamp the feedback voltage to ground potential during the on-time of the primary switch depends on the primary winding voltage (approximately equal to the rectified mains input voltage), the primary to feedback turns ratio, and resistor RFB1. The controller measures feedback source current and so enables RFB1 to set the input voltage start threshold and the input undervoltage protection threshold, as described below. Input Voltage Start Threshold In Initialise mode, the LinkSwitch-4 issues a single short-duration drive pulse in order to measure the primary voltage and so the approximate mains input voltage. If the input voltage is below VMAINS(START) then the LinkSwitch-4 will not start. Instead it will pause while V VCC discharges below V VCC(SLEEP) then it will begin a new power-up cycle. If the input voltage exceeds VMAINS(START), the converter will power-up. VMAINS(START) is set by RFB1 using this equation: V MAINS^START h = N -1 # I FBHT^START h # R FB1 # N P F 2 Input Undervoltage Protection In Run mode, if the mains voltage falls to VMAINS(LO), the LinkSwitch-4 will stop issuing drive pulses, V VCC will reduce to V VCC(SLEEP) and the LinkSwitch-4 will enter Sleep mode. VMAINS(LO) is set by RFB1 using this equation: V MAINS^LOh = N -1 # I FBHT^LOh # R FB1 # N P F 2 Constant Current (CC Mode) Regulation Constant current output (IOUT(CC)) is achieved by regulating the CS input to the primary side estimate of the output current scaled by RCS, VCS(CC). The regulated output current, IOUT(CC) is set by the value of the current sense resistor, RCS, and the transformer primary to secondary turns ratio (NP/NS). The value of RCS is determined using the formula: VCS^CC h ^Typh N n R CS . a N P kd S I OUT^CC h ^Typh The tolerance of RCS affects the accuracy of output the current regulation so is typically chosen to be 1%. The LinkSwitch-4 can maintain CC regulation down to much lower levels of VSHUTDN(MAX) normally specified for mobile phones chargers (see Figure 11). 5 www.power.com Rev. F 05/18 LinkSwitch-4 Cable Compensation If required, LinkSwitch-4 adjusts the converter output voltage (VOUT) to compensate for voltage drop across the output cable. The amount of compensation applied (GCAB) is specified by using the formula below to match cable compensation with output cable resistance (RCAB): G CAB = Or G CAB = I OUT^ CC h ^ Typ h # R CAB # 100% VOUT^ CV h ^ Typ h I OUT^ CP h ^ Typ h # R CAB # 100% VOUT^ CV h ^ Typ h Drive Pulse and Frequency Modulation The LinkSwitch-4 control circuitry determines both the primary switch peak current and the switching frequency to control output power, ensuring discontinuous conduction mode operation at all times. Primary current generates a voltage across the current sense resistor, RCS, and is sensed by the primary current sense input. The voltage on the primary CURRENT SENSE pin is negative-going, as shown in Figure 8. When the voltage exceeds a (negative) threshold (VCSTHR) set by the control circuitry, base drive is driven low to turn the primary switch off. The primary current sense voltage threshold (VCSTHR) varies from VCS(MIN) to VCS(MAX) during normal operation. The switching frequency varies from fMIN at no-load, to the maximum switching frequency, fMAX. Minimum switching frequency occurs during no-load operation and is typically in the range 1 to 3 kHz, depending on application design. The periodic voltage waveform on the VCC input, which depends on the current consumed by the control circuitry and the value of C VCC, contributes to control of the switching frequency. In no-load condition, C VCC must be large enough to ensure that ripple voltage on VCC (∆V VCCPFM) is less than 1.6 V, and C VCC must be small enough to ensure the ripple on VCC is greater than 50 mV: C VCC = I VCCNL fMIN # DVVCCPFM The switching frequency increases as the load increases, eventually reaching fMAX at full load. For protection purposes in the event of certain transitory conditions, the controller immediately issues a drive pulse if VCC voltage falls to V VCC(LOW). This is not part of normal operation or normal frequency control. Base Drive Control During the on-time of the BJT, the emitter is switched to GND via the EMITTER DRIVE pin. Base current, IBD is controlled to achieve fast turn-on, low on-voltage and fast turn-off to enable reduced power dissipation and accurate timing of each part of the switching cycle. As shown in Figure 9, the base drive current starts with a fixed pulse of IF(ON)/tF(ON). Its amplitude and duration are then modulated to provide sufficient charge for low BJT on-voltage, while allowing de-saturation towards the end of on-time so as to enable fast turn-off. When VCSTHR is detected on the primary CURRENT SENSE pin, the BASE DRIVE pin is switched to GND and the emitter drive switch is opened. LNK43x2S – drive optimized for high efficiency performance using 13003 transistors. Duty Cycle Control Maximum duty cycle is a function of the primary to secondary turns ratio of the transformer (typically 16:1 for a 5 V output). For a universal mains input power supply, maximum duty cycle is typically chosen to be 50% at the minimum (including ripple) of the rectified mains voltage (typically 80 V). Quasi-Resonant Switching The primary switch is turned on when the voltage across it rings down to a minimum (voltage-valley, quasi-resonant switching). The effect of this is to reduce losses in the switch at turn-on. It also helps reduce EMI. Primary Switch Over-Current Protection The primary switch is turned off if the emitter current sensed by the primary current sense input exceeds the effective threshold VCSOCP(EFF), subject to the minimum on-time, TON(MIN). The effective threshold VCSOCP(EFF) depends on a threshold VCS(OCP) predefined by the controller, the primary current sense signal rate of rise (dVcs/dt), which is dependent on the application design, and the primary CURRENT SENSE pin turn-off response time, tCS(OFF). This gives pulse by pulse over-current protection of the primary switch. Output Overvoltage Protection The on-time of the primary switch is reduced if the output voltage tends to VOUT(OVP). The value depends on the set output voltage (VOUT(CV)) and the feedback OVP ratio: VOUT^OVPh = VOUT^CV h # G FB^OVPh Supplementary Base Drive (LNK40x3D, LNK4114D, LNK4214D) The resistor RSBD connects the SUPPLEMENTARY BASE DRIVE pin to VOLTAGE SUPPLY pin. It supplements current to the base drive to optimize the switching bipolar transistor turn-on and turn-off in high power applications. Suggested values for the supplementary base drive resistor RSBD are between 220 Ω and 390 Ω. Shunt Function (LNK40x3D, LNK40x4D, LNK4115D, LNK4215D) The shunt function is intended to automatically limit the VCC voltage and allow greater flexibility in transformer design. VOLTAGE SUPPLY pin will be shunted via RSBD, the SUPPLEMENTARY BASE DRIVE pin resistance RSBD(ON) and RBD(OFF) to the GROUND pin when the VCC voltage is greater than V VCC(HI) and the transformer is discharging. Output Undervoltage Protection (LNK40x3S/D, LNK43x3S/D) The output undervoltage protection (UVP) function is used to shutdown the converter when the output voltage is below VOUT(UVP). At start-up this function is disabled during the first NSTARTUP switching cycles and the output current is regulated allowing the output voltage to rise from 0 V in a monotonic way. Product Output Undervoltage Protection Function LNK40x2S LNK43x2S VOUT(UVP) Depends on V VCC(SLEEP) LNK40x3S LNK40x3D LNK4323S LNK4323D VOUT(UVP) = 0.63 × VOUT(CV) LNK40x4D VOUT(UVP) Depends on V VCC(SLEEP) LNK4114D LNK4214D LNK4115D LNK4215D VOUT(UVP) Depends on V VCC(SLEEP) Table 3. Output Undervoltage Protection. 6 Rev. F 05/18 www.power.com LinkSwitch-4 If the output does not reach VOUT(UVP) during this time then the controller will shutdown and restart. VOUT(UVP) value depends on the set output voltage (VOUT(CV)) and the feedback UVP ratio: VOUT^UVPh = VOUT^CV h # G FB^UVPh Easy Start (LNK4114D, LNK4214D, LNK4115D, LNK4215D) The Easy Start feature guarantees start-up into large output capacitances and allows the output voltage to work down the CC chimney close to OV. The Easy Start feature uses the BJT emitter current (equal to the primary current) to charge the supply capacitor C VCC via an additional Schottky diode. This only occurs when the supply voltage has fallen below V VCCES and is achieved by altering the sequencing of EMITTER DRIVE pin switching. This allows the BJT emitter voltage to rise until the Schottky diode conducts. Emitter current then charges the C VCC until the BJT is turned off by the BASE DRIVE pin being pulled low. If the supply voltage is above V VCC(ES), then Easy Start has no effect on the operation of the controller. Note V VCC(ES) = 6 V for LNK4114D and LNK4214D, V VCC(ES) = 10 V for LNK43x3S, LNK43x3D, LNK4115D and LNK4215D during NSTARTUP cycles, after which it reduces to 6 V. Over-Temperature Protection Temperature protection is internal to LinkSwitch-4. The sensor measures the junction temperature TJ, which is the hottest part of LinkSwitch-4. At temperatures TJ ~ 140 °C, LinkSwitch-4 will shutdown and remain in this state until a temperature of TJ ~ 70 °C is reached. Whereby LinkSwitch-4 will power-up in the normal sequence. If the supply voltage is below V VCC(ES), and when the base has received enough charge, the EMITTER DRIVE pin is released at the same time as the BASE DRIVE pin. tFON IFON IBD IBDSRC Logic BD Logic ED BD Ground PI-7459-090215 Figure 9. Base Drive Waveforms. VCC tFON IBD IFON IBDSRC Logic BD Logic ED BD Ground CVCC Recharge Current PI-7674-090215 Figure 9b. Base Drive Waveforms – Easy Start mode of Operation. 7 www.power.com Rev. F 05/18 LinkSwitch-4 Typical Application for LNK40x3D Parameter Symbol Range or Value Units Supply Voltage VIN 85 - 265 VAC Output Voltage VOUT(CV) 5.0 ± 5% V Constant voltage (CV) mode, at the load Output Current IOUT 2 A Label rated output current Switching Frequency at Full Load fMAX 65 kHz Cable Compensation GCAB 6 % No-load Power PNL 75 % Energy Star test method TON 4 V Average Efficiency Turn-on Delay Undershoot Voltage Comment Universal mains Determined by the chosen variant Load step from 0 A to 0.5 A Table 4. 10 W Typical Application Results for Figure 10. T1 DOUT + COUT LFILT ROUT 2 × RHT DBRIDGE Q1 BD ~ CIN1 RIN RFB1 ED CIN2 LNK40x3D VCC RSBD CS RCS2 RCS GND SBD FB C VCC RFB2 PI-7679-071515 Figure 10. Typical Universal Input, 10 W Charger. By sensing the primary-side waveforms of transformer voltage and primary current, the LinkSwitch-4 achieves constant voltage and constant current output within tight limits without the need for any secondary-side sensing components. Figure 11 shows the output characteristics of a typical charger implementation. 8 Rev. F 05/18 www.power.com LinkSwitch-4 PI-7471-121014 VOUT 100% VOUTCV(TYP) IOUTCC(TYP) IOUTCC(MIN) VSHUTDN(MAX) IOUT 0 100% Figure 11. Typical CV/CC Output Characteristic Achieved. 9 www.power.com Rev. F 05/18 LinkSwitch-4 Typical Networking Application for LNK4114D Parameter Symbol Range or Value Units Supply Voltage VIN 90 - 264 VAC Output Voltage VOUT(CV) 12.0 ± 5% V Constant voltage (CV) mode, at the load Output Current IOUT 1 A Label rated output current Load Capacitance CLOAD 3000 mF System capacitance Switching Frequency at Full Load fMAX 65 kHz Cable Compensation GCAB 3 % No-load Power PNL 83 % Energy Star test method TON