COMPMIN CS CCLIM Oscillator CC Amplifier Limits …

1 RED2511. LED Controller for LLC converters Features Advanced LED Controller IC for high efficiency low-cost LLC converters with bipolar transistors and integrated PFC. PSR - +/-5% Primary Side Regulation of LED current and voltage with no Flicker SO8. 50% duty cycle, variable frequency control of resonant half-bridge Automatic dead-time control and Applications capacitive mode protection Single stage PFC LED drivers without flicker Protection modes: CC LED drivers 5-100W. Overload No-Load Internal Over-temperature Order code External Over-temperature (NTC). Control Loop Fault protection Part Number Package Packaging Low output capacitance allows live LED RED2511AD-TR13 SO8 Tape and reel connection Very low output current ripple <5%. Small SO8 IC package RC VDD. VDD. VREF ISTART. CV Amplifier TX1. - SLEEP. VFB Analog + VCOMPMAX +. Primary Control CLK Driver Side Logic Limits - Sensing Oscillator CS - VCOMPMIN RC RESET. VCCLIM +. SHUTDOWN. VFB VFB CC Amplifier VCOMPMIN=>Max Frequency ISTART.

2 high Low CS Voltage Low TX2. FAULTS. Fault Logic NTC Shutdown VDD. INTC IOTP. NTC - STARTUP. VNTC + Internal SLEEP. Over Temperature Shunt Startup RUN. Protection Regulator POR. GND. Figure 1: Block diagram 1/13 September 2015. RED2511 Datasheet Rev02. Preliminary RED2511 LED LLC Controller Device Pins VFB 1 8 CS. NTC 2 7 GND. TX2 3 6 VDD. TX1 4 5 RC. Figure 2: SO8 pin connections (top view). Pin Functions Pin # Name Function 1 VFB PSR Feedback input for output voltage regulation. Connect to primary sense winding. Shutdown pin that can be used for over-temperature protection with an external NTC resistor. A. 2 NTC. voltage of <VNTC will shut the IC down. Pin also includes a current source. 3 TX2 Output to control transformer. 4 TX1 Output to control transformer. 5 RC External RC network sets the minimum [full power] switching frequency. 6 VDD IC Power Supply pin nominally 7 GND Chip ground. PSR Current Sense input provides output current regulation and cycle-by-cycle over-current 8 CS.

3 Protection. The CS pin is connected to the half-bridge current sense resistor 2/13 September 2015. RED2511 Datasheet Rev02. Preliminary RED2511 LED LLC Controller Typical Application HT+. Q1 VOUT. T1. T2. +. T1a D1 Cout T1d Ls Output Lm _. D2. Q2. Daux Cr T1b Rcs Caux HT- Raux Rfb1. RNTC. T1c 4 3 2 1. TX1 TX2 NTC VFB. U1 Rcs2 Rfb2. Rrc RED2511. RC VDD GND CS. 5 6 7 8. Crc Cdd Figure 3: Typical Application Schematic: LLC converter with RED2511 PSR controller Features RED2511 is an advanced CMOS control IC for disconnected, the RED2511 controls the resonant LLC converters. The RED2511 Primary maximum output voltage and enters fault-mode Side Regulation (PSR) control scheme accurately operation to keep the output voltage from rising controls the LED current and removes the need and to keep the power consumption low. for secondary side opto-coupler feedback, reducing cost and complexity. Protection Features RED2511 uses the CSOC (Controlled Self- There are 5 faults that can cause the IC to enter Oscillating converter ) scheme to drive two low- fault mode: cost bipolar transistors in a half-bridge VFB pin voltage rises too high (no LED.)

4 Configuration. RED2511 is optimized to work with connected). RediSem's LLC converter topology with VFB pin voltage falls too low (feedback integrated Power Factor Correction. resistor Rfb1 disconnected). Please contact RediSem for application design CS pin voltage is low (CS pin shorted to information for LED drivers with PFC. GND). Overtemperature fault (discussed later). Accurate Primary Side Regulation Operating frequency rises too high The RED2511 PSR scheme regulates the LED During these fault conditions, the IC will drive current by modulating the converter continually attempt re-starts. Between each re- frequency. Primary side current control enables start attempt there will be 8 dummy re-starts +/-5% LED current regulation. With the LED when the IC re-starts while the converter is off. 3/13 September 2015. RED2511 Datasheet Rev02. Preliminary RED2511 LED LLC Controller Additionally, if the output is short-circuit, the 125 C. The IC will restart the converter when the auxiliary power to the IC fails and the IC shuts IC temperature drops by 15 C.

5 Down. From this condition the IC automatically cyclically re-starts until the short-circuit has been Automatic Dead-Time Control removed. An important feature of the Controlled Self The IC also has an instantaneous cycle-by-cycle Oscillating converter is that the dead-time is over-current protection (OCP) level that will controlled naturally. Unlike MOSFET half-bridge terminate any cycle instantaneously should the converters, it is not necessary to program the current exceed a pre-set level. dead-time on RED2511. The bipolar switching transistors are turned on correctly through the Over-temperature Protection & Shutdown self-oscillation of the converter and turned off by RED2511 has an NTC shutdown pin that can be RED2511. This greatly simplifies the design used either in conjunction with a thermistor or process and improves the robustness of the LLC. with a logic signal. A high voltage on the NTC converter . pin will allow the converter to run and a low voltage will turn it off.

6 40uA is sourced from the Capacitive Mode Protection NTC pin to allow simple connection to a RED2511 includes a capacitive mode protection thermistor. A small amount of hysteresis is also feature which prevents the converter from applied to this pin. entering capacitive switching mode on a cycle-by- An internal over-temperature protection shuts cycle basis by limiting the minimum frequency. down the controller if the IC temperature exceeds This always ensures the Controlled Self Oscillating converter continues to oscillate correctly. 4/13 September 2015. RED2511 Datasheet Rev02. Preliminary RED2511 LED LLC Controller IC Operation clamp inside the IC regulates the VDD voltage to Startup, Shutdown and re-start (VDDREG). The IC current is now Figure 4 shows typical startup waveforms for approximately (IDDREG) plus any excess RED2511. In SLEEP mode the IDD current is current required to clamp VDD to If VDD. approximately 8uA (IDDSLEEP). Once VDD falls below (VDDREG) the Zener clamp turns reaches (VDDSTART) the IC enters STARTUP off and IDD reduces to (IDDREG) only.

7 If VDD. mode. During this period of approximately 7ms falls below (VDDSLEEP), the IC enters SLEEP. (512 cycles) Vdd is allowed to drop to or rise mode. In this condition IDD reduces to 8uA. to This gives time for the application to (IDDSLEEP). pull up the output voltage. After this the IC. enters RUN mode when the controlled Zener VDDSTART. VDDREG. VDDSLEEP. Power Down 10ms (512 cycles) Sleep VDD voltage IDDRUN. IDDSLEEP IDD current Startpulses TX1. TX2. TX1. TX2. TX1. TX2. TX1. TX2. TX1. TX2. TX2. TX1. TX2. TX1. TX2. TX1. TX2. TX1. TX Pin voltage RC Pin voltage CS Pin voltage SLEEP MODE STARTUP MODE RUN MODE SLEEP MODE STARTUP MODE. TIME. Figure 4: IC Start-up waveforms Output stage A diagram of the output stage can be seen in oscillation. A low on-state NMOS transistor is Figure 5. To start the converter oscillating the used to turn the bipolar transistors off. It is RED2511 issues start pulses through the TX pins controlled by the Oscillator off-time. The NMOS. during the first two cycles.

8 These start pulses device is turned to pull TX pin low, which are 500ns long (tTXSTART) and provide 14mA switches off the corresponding bipolar transistor (ITXSTART) current pulses from both TX1 and TX2 in the power converter half-bridge. pins. After this the converter self-oscillates and no longer needs start pulses to maintain VDD. Start Pulse ITXSTART. TX1 /. TX2. Clamp Time Figure 5: Output Stage Drive Stage 5/13 September 2015. RED2511 Datasheet Rev02. Preliminary RED2511 LED LLC Controller Primary Side Regulation (PSR). controlling the frequency. An Oscillator Control The converter 's output current and voltage are Voltage is fed into the Oscillator comparator to estimated by the RED2511 PSR scheme. Inside give the desired operating frequency. Figure 6. the IC there are two separate control loops that shows how the two current and voltage error control the converter output current (in CC mode) amplifiers and their compensation networks are and voltage (in CV mode). The RED2511 configured for a primary regulated LLC converter .

9 Regulates the output current and voltage by VFB Sensing Signal Rfb1. CCOMP. VDD. VFB Primary Sensing Signal - Detection Oscillator + CV Control Voltage VREF. Integrator VCOMPMAX. Rfb2. Limits VCOMPMIN. Main converter VCCREG. Primary Current +. RCFB. CS PSR CFB - CC. 100R Average Integrator Current CSAVG. CCFB. CS Resistor Figure 6: Error Amplifier Circuits 6/13 September 2015. RED2511 Datasheet Rev02. Preliminary RED2511 LED LLC Controller Main converter Primary Current CS. 100R. Pin CSAVG. + To Oscillator PSR average Comparator current estimator VCCREG - CS Resistor CC. Integrator +. Oscillator Reset VOCPTHR - OCP. Comparator Figure 7: RED2511 Current protection and control circuits terminates the current Oscillator on-time cycle. PSR Current Control The Oscillator is reset and the off-time begins Figure 7 shows the two current control methods resulting in the bipolar transistors turning off and used in the converter : the half-bridge commutating. This is repeated in 1. constant current (CC) regulation; subsequent cycles whenever the CS voltage 2.

10 An instantaneous peak current limit exceeds the threshold. However, in a correctly (OCP). designed converter it should not be possible to trip OCP in normal operation. PSR Average current estimation Shown in figure 7 the signal from the CS pin is PSR Voltage Control divided into two different paths. The bottom path RED2511 features an internally compensated CV. provides peak instantaneous over-current control loop to control the maximum LED. protection (OCP) while the PSR Average Current converter output voltage. The VFB input senses estimation block provides the current regulation the output voltage from an auxiliary winding on (CC) information. The voltage on the CS pin is the primary side of the transformer. This signal is an AC signal biased around GND. Inside the conditioned in the PSR block and compared to a PSR block this signal is processed to provide a voltage reference of (VREF) inside the IC. voltage proportional to the average converter output current. In CV mode the VFB pin is regulated to VREF by adjusting the internal control voltage and Constant Current Regulation therefore the converter operating frequency.