SBR10U45SP5

A Product Line of Diodes Incorporated ZXLD1370 60V HIGH ACCURACY BUCK/BOOST/BUCK-BOOST LED DRIVER CONTROLLER Description The ZXLD1370 is an LED driver controller IC for driving external MOSFETs to drive high current LEDs. It is a multitopology controller enabling it to efficiently control the current through series connected LEDs. The multi-topology enables it to operate in buck, boost and buck-boost configurations. The 60V capability coupled with its multi-topology capability enables it to be used in a wide range of applications and drive in excess of 15 LEDs in series. The ZXLD1370 is a modified hysteretic controller using a patent pending control scheme providing high output current accuracy in all three modes of operation. High accuracy dimming is achieved through DC control and high frequency PWM control. The ZXLD1370 uses two pins for fault diagnosis. A flag output highlights a fault, while the multi-level status pin gives further information on the exact fault. Pin Assignments TSSOP-16 EP Features • • • • • 0.5% typical output current accuracy 6 to 60V operating voltage range LED driver supports Buck, Boost and Buck-boost configurations Wide dynamic range dimming o 20:1 DC dimming o 1000:1 dimming range at 500Hz Up to 1MHz switching High temperature control of LED current using TADJ • • Typical Application Circuit Buck-boost diagram utilizing thermistor and Tadj Curve showing LED current vs. TLED ZXLD1370 Document number: DS32165 Rev. 2 - 2 1 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Pin Descriptions Pin Name Pin Type‡ Description Adjust input (for dc output current control) Connect to REF to set 100% output current. Drive with dc voltage (125mV 0.32V) Normal operation No load Sourcing 1mA (Note 7) Sinking 1mA, (Note 8) VIN = VAU X= VISM = 18V IGATE = 1mA Charging or discharging gate of external switch with QG = 10nC and 400kHz Min Typ Max 0.5 1 4.8 3.9 3.9 3.9 2.1 1.2 Units V µA 4.2 3.3 3.3 3.3 1.5 0.6 4.5 3.6 3.6 3.6 1.8 0.9 10 STATUS Flag no-load output voltage VSTATUS (Note 5) V RSTATUS Output impedance of STATUS output Driver output (PIN GATE) VGATEH High level output voltage VGATEL Low level output voltage kΩ V 0.5 V V mA 10 11 VGATECL High level GATE CLAMP voltage IGATE Dynamic peak current available during rise or fall of output voltage 12.8 ±300 15 Time to assert ‘STALL’ flag and warning on STATUS output GATE low or high (Note 9) LED Thermal control circuit (TADJ) parameters Upper threshold voltage Onset of output current reduction VTADJH (VTADJ falling) Lower threshold voltage Output current reduced to 500kHz 15 13 Number of LEDs 11 9 7 5 L=33uH 3 L=10uH 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=22uH L=47uH Figure 20: 1.5A Buck mode inductor selection for target frequency > 500kHz For example, in a buck configuration (VIN =24V and 6 LEDs), with a load current of 1.5A; if the target frequency is around 400 kHz, the Ideal inductor size is L= 33µH. The same kind of graphs can be used to select the right inductor for a buck configuration and a LED current of 750mA, as shown in figures 21 and 22. ZXLD1370 Buck Mode 750mA Minimum Recommended Inductor Target Switching frequency 400kHz 15 13 Number of LEDs 11 9 7 5 L=68uH 3 L=33uH 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=47uH L=100uH Figure 21: 750mA Buck mode inductor selection for target frequency 400kHz ZXLD1370 Document number: DS32165 Rev. 2 - 2 15 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 ZXLD1370 Buck Mode 750mA Minimum Recommended Inductor Target Switching frequency > 500kHz 15 13 Number of LEDs 11 9 7 5 3 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=47uH L=33uH L=68uH L=100uH Figure 22: 750mA Buck mode inductor selection for target frequency > 500kHz In the case of the Buck-boost topology, the following graphs guide the designer to select the inductor for a target frequency of 400kHz (figure 23) or higher than 500kHz (figure 24). ZXLD1370 Buck-Boost Mode 350mA Minimum Recommended Inductor Target Switching frequency - 400kHz 15 13 Number of LEDs 11 9 7 5 L=33uH 3 L=22uH 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=47uH Figure 23: 350mA Buck-Boost mode inductor selection for target frequency 400kHz ZXLD1370 Document number: DS32165 Rev. 2 - 2 16 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 ZXLD1370 Buck-Boost Mode 350mA Minimum Recommended Inductor Target Switching frequency > 500kHz 15 13 Number of LEDs 11 9 7 5 3 L=22uH 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=33uH L=47uH Figure 24: 350mA Buck-Boost mode inductor selection for target frequency > 500kHz For example, in a Buck-bust configuration (VIN =10-18V and 4 LEDs), with a load current of 350mA; if the target frequency is around 400kHz, the Ideal inductor size is L= 33uH. The same size of inductor can be used if the target frequency is higher than 500kHz driving 6LEDs with a current of 350mA from a VIN =12-24V. In the case of the Boost topology, the following graphs guide the designer to select the inductor for a target frequency of 400kHz (figure 25) or higher than 500kHz (figure 26). ZXLD1370 Boost Mode 350mA Minimum Recommended Inductor Target Switching frequency - 400kHz 15 13 Number of LEDs 11 9 7 5 3 1 0 10 20 L=22uH L=47uH L=33uH 30 Supply Voltage (V) 40 50 60 Figure 25: 350mA Boost mode inductor selection for target frequency 400kHz ZXLD1370 Document number: DS32165 Rev. 2 - 2 17 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 ZXLD1370 Boost Mode 350mA Minimum Recommended Inductor Target Switching frequency > 500kHz L=47uH 15 13 Number of LEDs 11 9 7 5 3 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=22uH L=33uH Figure 26: 350mA Buck-Boost mode inductor selection for target frequency > 500kHz Suitable coils for use with the ZXLD1370 may be selected from the MSS range manufactured by Coilcraft, or the NPIS range manufactured by NIC components. The following websites may be useful in finding suitable components www.coilcraft.com www.niccomp.com www.wuerth-elektronik.de MOSFET Selection The ZXLD130 requires an external NMOS FET as the main power switch with a voltage rating at least 15% higher than the maximum transistor voltage to ensure safe operation during the ringing of the switch node. The current rating is recommended to be at least 10% higher than the average transistor current. The power rating is then verified by calculating the resistive and switching power losses. P = Presistive + Pswitching Resistive power losses The resistive power losses are calculated using the RMS transistor current and the MOSFET on-resistance. Calculate the current for the different topologies as follows: Buck mode IMOSFET −MAX = D MAX x ILED Boost / Buck-boost mode IMOSFET −MAX = D MAX x ILED 1 − DMAX The approximate RMS current in the MOSFET will be: Buck mode IMOSFET −RMS =ILED D Boost / Buck-boost mode IMOSFET −RMS = D x ILED 1− D 18 of 33 www.diodes.com May 2010 © Diodes Incorporated ZXLD1370 Document number: DS32165 Rev. 2 - 2 A Product Line of Diodes Incorporated ZXLD1370 The resistive power dissipation of the MOSFET is: Presistive = IMOSFET−RMS x RDS −ON 2 Switching power losses Calculating the switching MOSFET's switching loss depends on many factors that influence both turn-on and turn-off. Using a first order rough approximation, the switching power dissipation of the MOSFET is: Pswitching = CRSS x V 2 IN x fsw x ILOAD IGATE where CRSS is the MOSFET's reverse-transfer capacitance (a data sheet parameter), fSW is the switching frequency, IGATE is the MOSFET gate-driver's sink/source current at the MOSFET's turn-on threshold. Matching the MOSFET with the controller is primarily based on the rise and fall time of the gate voltage. The best rise/fall time in the application is based on many requirements, such as EMI (conducted and radiated), switching losses, lead/circuit inductance, switching frequency, etc. How fast a MOSFET can be turned on and off is related to how fast the gate capacitance of the MOSFET can be charged and discharged. The relationship between C (and the relative total gate charge Qg), turn-on/turn-off time and the MOSFET driver current rating can be written as: dt = dV ⋅ C Qg = I I where dt = turn-on/turn-off time dV = gate voltage C = gate capacitance = Qg/V I = drive current – constant current source (for the given voltage value) Here the constant current source” I ” usually is approximated with the peak drive current at a given driver input voltage. Example 1) Using the DMN6068 MOSFET (VDS(MAX) = 60V, ID(MAX) = 8.5A): QG = 10.3nC at VGS = 10V ZXLD1370 IPEAK = I GATE = 300mA dt = Qg IPEAK = 10.3nC = 35ns 300mA Assuming that cumulatively the rise time and fall time can account for a maximum of 10% of the period, the maximum frequency allowed in this condition is: tPERIOD = 20*dt f = 1/ tPERIOD = 1.43MHz This frequency is well above the max frequency the device can handle, therefore the DNM6068 can be used with the ZXLD1370 in the whole spectrum of frequencies recommended for the device (from 300kHz to 1MHz). Example 2) Using the ZXMN6A09K (VDS(MAX) = 60V, ID(MAX) = 12.2A): QG = 29nC at VGS = 10V ZXLD1370 IPEAK = 300mA dt = Qg IPEAK = 29nC = 97ns 300mA Assuming that cumulatively the rise time and fall time can account for a maximum of 10% of the period, the maximum frequency allowed in this condition is: tPERIOD = 20*dt f = 1/ tPERIOD = 515kHz This frequency is within the recommended frequency range the device can handle, therefore the ZXMN6A09K is recommended to be used with the ZXLD1370 for frequencies from 300kHz to 500kHz). The recommended total gate charge for the MOSFET used in conjunction with the ZXLD1370 is less than 30nC. ZXLD1370 Document number: DS32165 Rev. 2 - 2 19 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Junction temperature estimation Finally, the ZXLD1370 junction temperature can be estimated using the following equations: Total supply current of ZXLD1370: IQTOT ≈ IQ + f • QG Where IQ = total quiescent current IQ-IN + IQ-AUX Power consumed by ZXLD1370 PIC = VIN • (IQ + f • Qg) Or in case of separate voltage supply, with VAUX < 15V PIC = VIN • IQ-IN + Vaux • (IQ-AUX + f • Qg) TJ = TA + PIC • RTH(JA)= TA + PIC • (RTH(JC)+ RTH(CA)) Where the total quiescent current IQTOT consists of the static supply current (IQ) and the current required to charge and discharge the gate of the power MOSFET. Moreover the part of thermal resistance between case and ambient depends on the PCB characteristics. DIODE SELECTION For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode* with low reverse leakage at the maximum operating voltage and temperature. The Schottky diode also provides better efficiency than silicon PN diodes, due to a combination of lower forward voltage and reduced recovery time. It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than the maximum output load current. In particular, it is recommended to have a voltage rating at least 15% higher than the maximum transistor voltage to ensure safe operation during the ringing of the switch node and a current rating at least 10% higher than the average diode current. The power rating is verified by calculating the power loss through the diode. The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on the Drain of the external MOSFET. If a silicon diode is used, care should be taken to ensure that the total voltage appearing on the Drain of the external MOSFET, including supply ripple, does not exceed the specified maximum value. *A suitable Schottky diode would be PDS3100 (Diodes Inc). OUTPUT CAPACITOR An output capacitor may be required to limit interference or for specific EMC purposes. For boost and buck-boost regulators, the output capacitor provides energy to the load when the freewheeling diode is reverse biased during the first switching subinterval. An output capacitor in a buck topology will simply reduce the LED current ripple below the inductor current ripple. In other words, this capacitor changes the current waveform through the LED(s) from a triangular ramp to a more sinusoidal version without altering the mean current value. In all cases, the output capacitor is chosen to provide a desired current ripple of the LED current (usually recommended to be less than 40% of the average LED current). Buck: C OUTPUT = 8 x fSW ΔIL −PP x rLED x ΔILED −PP Boost and Buck-boost C OUTPUT = where: • • • • fSW D x ILED −PP x rLED x ΔILED −PP ΔIL is the ripple of the inductor current, usually ± 20% of the average sensed current ΔILED is the ripple of the LED current, it should be 0.32V FLAG H L L L L L L Nominal STATUS voltage 4.5 4.5 3.6 3.6 3.6 1.8 0.9 9. Severity 1 denotes lowest severity. 10. This warning will be indicated if the output power demand is higher than the available input power; the loop may not be able to maintain regulation. 11. This warning will be indicated if the gate pin stays at the same level for greater than 100us (e.g. the output transistor cannot pass enough current to reach the upper switching threshold). FLAG VOLTAGE V REF 0V 4.5V Normal Operations 3.6V VAUX UVLO STATUS VOLTAGE - VIN UVLO - STALL - OUT of REG 2.7V 1.8V Over Temperature 0.9V Over Current 0A 0 1 2 SEVERITY 3 4 Fig 34: Status levels In the event of more than one fault/warning condition occurring, the higher severity condition will take precedence. E.g. ‘Excessive coil current’ and ‘Out of regulation’ occurring together will produce an output of 0.9V on the STATUS pin. If VADJ>1.7V, VSENSE may be greater than the excess coil current threshold in normal operation and an error will be reported. Hence, STATUS and FLAG are only guaranteed for VADJ